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Semantic Definition Format (SDF) for Data and Interactions of Things
draft-ietf-asdf-sdf-17

Document Type Active Internet-Draft (asdf WG)
Authors Michael Koster , Carsten Bormann , Ari Keränen
Last updated 2023-11-05
Replaces draft-onedm-t2trg-sdf
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
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May 2022
SDF specification, publication requested
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Shepherd write-up Show Last changed 2023-10-12
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draft-ietf-asdf-sdf-17
ASDF                                                      M. Koster, Ed.
Internet-Draft                                                       KTC
Intended status: Standards Track                         C. Bormann, Ed.
Expires: 8 May 2024                               Universität Bremen TZI
                                                              A. Keränen
                                                                Ericsson
                                                         5 November 2023

  Semantic Definition Format (SDF) for Data and Interactions of Things
                         draft-ietf-asdf-sdf-17

Abstract

   The Semantic Definition Format (SDF) is a format for domain experts
   to use in the creation and maintenance of data and interaction models
   that describe Things, i.e., physical objects that are available for
   interaction over a network.  An SDF specification describes
   definitions of SDF Objects/SDF Things and their associated
   interactions (Events, Actions, Properties), as well as the Data types
   for the information exchanged in those interactions.  Tools convert
   this format to database formats and other serializations as needed.

   // The present revision (-17) addresses additional Working Group Last
   // Call comments that came in during a grace period added.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-asdf-sdf/.

   Discussion of this document takes place on the A Semantic Definition
   Format for Data and Interactions of Things (ASDF) Working Group
   mailing list (mailto:asdf@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/asdf/.  Subscribe at
   https://www.ietf.org/mailman/listinfo/asdf/.

   Source for this draft and an issue tracker can be found at
   https://github.com/ietf-wg-asdf/SDF.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 8 May 2024.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Terminology and Conventions . . . . . . . . . . . . . . .   4
   2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     2.1.  Example Definition  . . . . . . . . . . . . . . . . . . .   7
     2.2.  Elements of an SDF model  . . . . . . . . . . . . . . . .   9
       2.2.1.  sdfObject . . . . . . . . . . . . . . . . . . . . . .  10
       2.2.2.  sdfProperty . . . . . . . . . . . . . . . . . . . . .  11
       2.2.3.  sdfAction . . . . . . . . . . . . . . . . . . . . . .  12
       2.2.4.  sdfEvent  . . . . . . . . . . . . . . . . . . . . . .  12
       2.2.5.  sdfData . . . . . . . . . . . . . . . . . . . . . . .  13
       2.2.6.  sdfThing  . . . . . . . . . . . . . . . . . . . . . .  13
     2.3.  Member names: Given Names and Quality Names . . . . . . .  14
       2.3.1.  Given Names and Quality Names . . . . . . . . . . . .  14
       2.3.2.  Hierarchical Names  . . . . . . . . . . . . . . . . .  14
       2.3.3.  Extensibility of Given Names and Quality Names  . . .  15
   3.  SDF structure . . . . . . . . . . . . . . . . . . . . . . . .  16
     3.1.  Information block . . . . . . . . . . . . . . . . . . . .  16
     3.2.  Namespaces block  . . . . . . . . . . . . . . . . . . . .  18
     3.3.  Definitions block . . . . . . . . . . . . . . . . . . . .  19
   4.  Names and namespaces  . . . . . . . . . . . . . . . . . . . .  20

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     4.1.  Structure . . . . . . . . . . . . . . . . . . . . . . . .  21
     4.2.  Contributing global names . . . . . . . . . . . . . . . .  21
     4.3.  Referencing global names  . . . . . . . . . . . . . . . .  22
     4.4.  sdfRef  . . . . . . . . . . . . . . . . . . . . . . . . .  23
       4.4.1.  Resolved models . . . . . . . . . . . . . . . . . . .  25
     4.5.  sdfRequired . . . . . . . . . . . . . . . . . . . . . . .  26
     4.6.  Common Qualities  . . . . . . . . . . . . . . . . . . . .  29
     4.7.  Data Qualities  . . . . . . . . . . . . . . . . . . . . .  29
       4.7.1.  sdfType . . . . . . . . . . . . . . . . . . . . . . .  31
       4.7.2.  sdfChoice . . . . . . . . . . . . . . . . . . . . . .  32
   5.  Keywords for definition groups  . . . . . . . . . . . . . . .  34
     5.1.  sdfObject . . . . . . . . . . . . . . . . . . . . . . . .  34
     5.2.  sdfProperty . . . . . . . . . . . . . . . . . . . . . . .  35
     5.3.  sdfAction . . . . . . . . . . . . . . . . . . . . . . . .  36
     5.4.  sdfEvent  . . . . . . . . . . . . . . . . . . . . . . . .  37
     5.5.  sdfData . . . . . . . . . . . . . . . . . . . . . . . . .  37
   6.  High Level Composition  . . . . . . . . . . . . . . . . . . .  38
     6.1.  Paths in the model namespaces . . . . . . . . . . . . . .  38
     6.2.  Modular Composition . . . . . . . . . . . . . . . . . . .  38
       6.2.1.  Use of the "sdfRef" keyword to re-use a definition  .  39
     6.3.  sdfThing  . . . . . . . . . . . . . . . . . . . . . . . .  40
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  41
     7.1.  Media Type  . . . . . . . . . . . . . . . . . . . . . . .  41
     7.2.  Content-Format  . . . . . . . . . . . . . . . . . . . . .  42
     7.3.  IETF URN Sub-namespace for Unit Names
           (urn:ietf:params:unit)  . . . . . . . . . . . . . . . . .  43
     7.4.  Registries  . . . . . . . . . . . . . . . . . . . . . . .  43
       7.4.1.  Quality Name Prefixes . . . . . . . . . . . . . . . .  43
       7.4.2.  sdfType Values  . . . . . . . . . . . . . . . . . . .  44
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  45
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  45
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  45
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  47
   Appendix A.  Formal Syntax of SDF . . . . . . . . . . . . . . . .  49
   Appendix B.  json-schema.org Rendition of SDF Syntax  . . . . . .  54
   Appendix C.  Data Qualities inspired by json-schema.org . . . . .  96
     C.1.  type "number", type "integer" . . . . . . . . . . . . . .  97
     C.2.  type "string" . . . . . . . . . . . . . . . . . . . . . .  97
     C.3.  type "boolean"  . . . . . . . . . . . . . . . . . . . . .  98
     C.4.  type "array"  . . . . . . . . . . . . . . . . . . . . . .  98
     C.5.  type "object" . . . . . . . . . . . . . . . . . . . . . .  99
     C.6.  Implementation notes  . . . . . . . . . . . . . . . . . .  99
   Appendix D.  Composition Examples . . . . . . . . . . . . . . . .  99
     D.1.  Outlet Strip Example  . . . . . . . . . . . . . . . . . .  99
     D.2.  Refrigerator-Freezer Example  . . . . . . . . . . . . . . 100
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . . 102
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . . 102
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 102

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1.  Introduction

   The Semantic Definition Format (SDF) is a format for domain experts
   to use in the creation and maintenance of data and interaction models
   that describe Things, i.e., physical objects that are available for
   interaction over a network.  An SDF specification describes
   definitions of SDF Objects/SDF Things and their associated
   interactions (Events, Actions, Properties), as well as the Data types
   for the information exchanged in those interactions.  Tools convert
   this format to database formats and other serializations as needed.

   // The present revision (-17) addresses additional Working Group Last
   // Call comments that came in during a grace period added.

   SDF is designed to be an extensible format.  The present document
   constitutes the base specification for SDF; we speak of "base SDF"
   for short.  In addition, SDF extensions can be defined, some of which
   may make use of extension points specifically defined for this in
   base SDF.  One area for such extensions would be refinements of SDF's
   abstract interaction models into protocol bindings for specific
   ecosystems (e.g., [I-D.bormann-asdf-sdf-mapping]).  For other
   extensions, it may be necessary to indicate in the SDF document that
   a specific extension is in effect; see Section 3.1 for details of the
   features quality that can be used for such indications.  With
   extension points and feature indications available, base SDF does not
   define a "version" concept for the SDF format itself (as opposed to
   version indications within SDF documents indicating their own
   evolution, see Section 3.1).

1.1.  Terminology and Conventions

   Thing:  A physical item that is also available for interaction over a
      network.

   Grouping:  An sdfThing or sdfObject, i.e., (directly or indirectly) a
      combination of Affordances.

   sdfThing:  A grouping of Groupings as well as potentially Affordance
      declarations (Property, Action, and Event declarations).

   Affordance:  An element of an interface offered for interaction, for
      which information is available (directly or indirectly) that
      indicates how it can or should be used.  The term is used here for
      the digital (network-directed) interfaces of a Thing only; it
      might also have physical affordances such as buttons, dials, and
      displays.

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   Quality:  A metadata item in a definition or declaration which says
      something about that definition or declaration.  A quality is
      represented in SDF as an entry in a JSON map (JSON object) that
      serves as a definition or declaration.

   Entry:  A key-value pair in a map.  (In JSON maps, sometimes also
      called "member".)

   Block:  One or more entries in a JSON map that is part of an SDF
      specification; these entries together serve a specific function.

   Group:  An entry in the main JSON map representing the SDF document,
      and in certain nested definitions, that has a Class Name Keyword
      as its key and a map of named definition entries (Definition
      Group) as a value.

   Class Name Keyword:  One of sdfThing, sdfObject, sdfProperty,
      sdfAction, sdfEvent, or sdfData; the Classes for these type
      keywords are capitalized and prefixed with sdf.

   Class:  Abstract term for the information that is contained in groups
      identified by a Class Name Keyword.

   Property:  An affordance that can potentially be used to read, write,
      and/or observe state (current/stored information) on an sdfObject.
      (Note that Entries are often called properties in other
      environments; in this document, the term Property is specifically
      reserved for affordances, even if the map key "properties" might
      be imported from a data definition language with the other
      semantics.)

   Action:  An affordance that can potentially be used to perform a
      named operation on an sdfObject.

   Event:  An affordance that can potentially be used to obtain
      information about what happened to an sdfObject.

   Object, sdfObject:  A grouping containing only Affordance
      declarations (Property, Action, and Event declarations); the main
      "atom" of reusable semantics for model construction. sdfObjects
      are similar to sdfThings but do not allow nesting, i.e., they
      cannot contain other Groupings (sdfObjects or sdfThings).  (Note
      that JSON maps are often called JSON objects due to JSON's
      JavaScript heritage; in the context of SDF, the term Object as the
      colloquial shorthand for sdfObject, is specifically reserved for
      the above grouping, even if the type name "object" is imported
      from a data definition language with the other semantics.)

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   Element:  A part or an aspect of something abstract; used here in its
      usual English definition.  (Occasionally, also used specifically
      for the elements of JSON arrays.)

   Definition:  An entry in a Definition Group; the entry creates a new
      semantic term for use in SDF models and associates it with a set
      of qualities.  Unless it is also a Declaration, a definition just
      defines a term, it does not create a component item within the
      enclosing definition.

   Declaration:  A definition within an enclosing definition, intended
      to create a component item within that enclosing definition.
      Every declaration can also be used as a definition for reference
      in a different place.

   SDF Document:  Container for SDF Definitions, together with data
      about the SDF Document itself (information block).  Represented as
      a JSON text representing a single JSON map, which is built from
      nested maps.

   SDF Model:  Definitions and declarations that model the digital
      interaction opportunities offered by one or more kinds of Things,
      represented by sdfObjects and sdfThings.  An SDF Model can be
      fully contained in a single SDF Document, or it can be built from
      an SDF Document that references definitions and declarations from
      additional SDF documents.

   Protocol Binding:  A companion document to an SDF Model that defines
      how to map the abstract concepts in the model into the protocols
      in use in a specific ecosystem.  Might supply URL components,
      numeric IDs, and similar details.  Protocol Bindings are one case
      of an Augmentation Mechanism.

   Augmentation Mechanism:  A companion document to a base SDF Model
      that provides additional information ("augments" the base
      specification), possibly for use in a specific ecosystem or with a
      specific protocol ("Protocol Binding").  No specific Augmentation
      Mechanisms are defined in base SDF.  A simple mechanism for such
      augmentations has been discussed as a "mapping file"
      [I-D.bormann-asdf-sdf-mapping].

   The term "byte" is used in its now-customary sense as a synonym for
   "octet".

   Conventions:

   *  The singular form is chosen as the preferred one for the keywords
      defined here.

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   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Overview

2.1.  Example Definition

   We start with an example for the SDF definition of a simple sdfObject
   called "Switch" (Figure 1).

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   {
     "info": {
       "title": "Example document for SDF (Semantic Definition Format)",
       "version": "2019-04-24",
       "copyright": "Copyright 2019 Example Corp. All rights reserved.",
       "license": "https://example.com/license"
     },
     "namespace": {
       "cap": "https://example.com/capability/cap"
     },
     "defaultNamespace": "cap",
     "sdfObject": {
       "Switch": {
         "sdfProperty": {
           "value": {
             "description":
   "The state of the switch; false for off and true for on.",
             "type": "boolean"
           }
         },
         "sdfAction": {
           "on": {
             "description":
   "Turn the switch on; equivalent to setting value to true."
           },
           "off": {
             "description":
   "Turn the switch off; equivalent to setting value to false."
           },
           "toggle": {
             "description":
   "Toggle the switch; equivalent to setting value to its complement."
           }
         }
       }
     }
   }

               Figure 1: A simple example of an SDF document

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   This is a model of a switch.  The state value declared in the
   sdfProperty group, represented by a Boolean, will be true for "on"
   and will be false for "off".  The actions on or off declared in the
   sdfAction group are redundant with setting the value and are in the
   example to illustrate that there are often different ways of
   achieving the same effect.  The action toggle will invert the value
   of the sdfProperty value, so that 2-way switches can be created;
   having such action will avoid the need for first retrieving the
   current value and then applying/setting the inverted value.

   The sdfObject group lists the affordances of Things modeled by this
   sdfObject.  The sdfProperty group lists the property affordances
   described by the model; these represent various perspectives on the
   state of the sdfObject.  Properties can have additional qualities to
   describe the state more precisely.  Properties can be annotated to be
   read, write or read/write; how this is actually done by the
   underlying transfer protocols is not described in the SDF model but
   left to companion protocol bindings.  Properties are often used with
   RESTful paradigms [I-D.irtf-t2trg-rest-iot], describing state.  The
   sdfAction group is the mechanism to describe other interactions in
   terms of their names, input, and output data (no data are used in the
   example), as in a POST method in REST or in a remote procedure call.
   The example toggle is an Action that changes the state based on the
   current state of the Property named value.  (The third type of
   affordance is Events, which are not described in this example.)

   In the JSON representation, note how (with the exception of the info
   group) maps that have keys taken from the SDF vocabulary (info,
   namespace, sdfObject) alternate in nesting with maps that have keys
   that are freely defined by the model writer (Switch, value, on,
   etc.); the latter usually use the named<> production in the formal
   syntax of SDF (Appendix A), while the former SDF-defined vocabulary
   items are often, but not always, called _qualities_.

2.2.  Elements of an SDF model

   The SDF language uses six predefined Class Name Keywords for modeling
   connected Things which are illustrated in Figure 2.

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                     ,--------.
                     |sdfThing|
                     |--------|
                     `--------'

               ,---------.
               |sdfObject|
               |---------|
               `---------'

   ,-----------.  ,---------.   ,--------.
   |sdfProperty|  |sdfAction|   |sdfEvent|
   |-----------|  |---------|   |--------|
   `-----------'  `---------'   `--------'
                       |

                   ,-------.
                   |sdfData|
                   |-------|
                   `-------'

                 Figure 2: Main classes used in SDF models

   The six main Class Name Keywords are discussed below.

2.2.1.  sdfObject

   sdfObjects, the items listed in an sdfObject definition group, are
   the main "atom" of reusable semantics for model construction.  The
   concept aligns in scope with common definition items from many IoT
   modeling systems, for example ZigBee Clusters [ZCL], OMA SpecWorks
   LwM2M Objects [OMA], and OCF Resource Types [OCF].

   An sdfObject contains a set of sdfProperty, sdfAction, and sdfEvent
   definitions that describe the interaction affordances associated with
   some scope of functionality.

   For the granularity of definition, sdfObject definitions are meant to
   be kept narrow enough in scope to enable broad reuse and
   interoperability.  For example, defining a light bulb using separate
   sdfObject definitions for on/off control, dimming, and color control
   affordances will enable interoperable functionality to be configured
   for diverse product types.  An sdfObject definition for a common on/
   off control may be used to control may different kinds of Things that
   require on/off control.

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   The presence of one or both of the optional qualities "minItems" and
   "maxItems" defines the sdfObject as an array, i.e., all the
   affordances defined for the sdfObject exist a number of times,
   indexed by a number constrained to be between minItems and maxItems,
   inclusive, if given.  (Note: Setting "minItems" to zero and leaving
   out "maxItems" puts the minimum constraints on that array.)

2.2.2.  sdfProperty

   sdfProperty is used to model elements of state within Things modeled
   by the enclosing grouping.

   A named definition entry in sdfProperty may be associated with some
   protocol affordance to enable the application to obtain the state
   variable and, optionally, modify the state variable.  Additionally,
   some protocols provide for in-time reporting of state changes.
   (These three aspects are described by the qualities readable,
   writable, and observable defined for an sdfProperty.)

   Definitions in sdfProperty groups include the definitions from
   sdfData groups, however, they actually also declare that a Property
   with the given qualities potentially is present in the containing
   sdfObject.

   For definitions in sdfProperty and sdfData, SDF provides qualities
   that can constrain the structure and values of data allowed in the
   interactions modeled by them, as well as qualities that associate
   semantics to these data, such as engineering units and unit scaling
   information.

   For the data definition within sdfProperty or sdfData, SDF borrows
   some vocabulary proposed for the drafts 4 [JSO4] [JSO4V] and 7 [JSO7]
   [JSO7V] of the json-schema.org "JSON Schema" format (collectively
   called JSO here), enhanced by qualities that are specific to SDF.
   Details about the JSO-inspired vocabulary are in Appendix C.  For
   base SDF, data are constrained to be of simple types (number, string,
   Boolean), JSON maps composed of named data, and arrays of these
   types.  Syntax extension points are provided that can be used to
   provide richer types in a future extension of this specification
   (possibly more of which can be borrowed from json-schema.org).

   Note that sdfProperty definitions (and sdfData definitions in
   general) are not intended to constrain the formats of data used for
   communication over network interfaces.  Where needed, data
   definitions for payloads of protocol messages are expected to be part
   of the protocol binding.

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2.2.3.  sdfAction

   The sdfAction group contains declarations of Actions, model
   affordances that, when triggered, have more effect than just reading,
   updating, or observing Thing state, often resulting in some outward
   physical effect (which, itself, cannot be modeled in SDF).  From a
   programmer's perspective, they might be considered to be roughly
   analogous to method calls.

   Actions may have data parameters; these are modeled as a single item
   of input data and output data, each.  (Where multiple parameters need
   to be modeled, an "object" type can be used to combine these
   parameters into one.)  Actions may be long-running, that is to say
   that the effects may not take place immediately as would be expected
   for an update to an sdfProperty; the effects may play out over time
   and emit action results.  Actions may also not always complete and
   may result in application errors, such as an item blocking the
   closing of an automatic door.

   One idiom for giving an action initiator status and control about the
   ongoing action is to provide a URI for an ephemeral "action resource"
   in the sdfAction output data, allowing the action to deliver
   immediate feedback (including errors that prevent the action from
   starting) and the action initiator to use the action resource for
   further observation or modification of the ongoing action (including
   canceling it).  Base SDF does not provide any tailored support for
   describing such action resources; an extension for modeling links in
   more detail (for instance, [I-D.bormann-asdf-sdftype-link]) may be
   all that is needed to fully enable modeling them.

   Actions may have (or lack) qualities of idempotency and side-effect
   safety.

   Base SDF only provides data constraint modeling and semantics for the
   input and output data of definitions in sdfAction groups.  Again,
   data definitions for payloads of protocol messages, and detailed
   protocol settings for invoking the action, are expected to be part of
   the protocol binding.

2.2.4.  sdfEvent

   The sdfEvent group contains declarations of Events, which can model
   affordances that inform about "happenings" associated with a Thing
   modeled by the enclosing sdfObject; these may result in a signal
   being stored or emitted as a result.

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   Note that there is a trivial overlap with sdfProperty state changes,
   which may also be defined as events but are not generally required to
   be defined as such.  However, Events may exhibit certain ordering,
   consistency, and reliability requirements that are expected to be
   supported in various implementations of sdfEvent that do distinguish
   sdfEvent from sdfProperty.  For instance, while a state change may
   simply be superseded by another state change, some events are
   "precious" and need to be preserved even if further events follow.

   Base SDF only provides data constraint modeling and semantics for the
   output data of Event affordances.  Again, data definitions for
   payloads of protocol messages, and detailed protocol settings for
   invoking the action, are expected to be part of the protocol binding.

2.2.5.  sdfData

   Definitions in sdfData groups do not themselves specify affordances.
   These definitions are provided separately from those in sdfProperty
   groups to enable common modeling patterns, data constraints, and
   semantic anchor concepts to be factored out for data items that make
   up sdfProperty items and serve as input and output data for sdfAction
   and sdfEvent items.  The sdfData definitions only spring to life by
   being referenced in one of these contexts (directly or indirectly via
   some other sdfData definitions).

   It is a common use case for such a data definition to be shared
   between an sdfProperty item and input or output parameters of an
   sdfAction or output data provided by an sdfEvent. sdfData definitions
   also enable factoring out extended application data types such as
   mode and machine state enumerations to be reused across multiple
   definitions that have similar basic characteristics and requirements.

2.2.6.  sdfThing

   Back at the top level, the sdfThing group enables definition of
   models for complex devices that will use one or more sdfObject
   definitions.  Like sdfObject, sdfThing groups also allow for
   including interaction affordances, sdfData, as well as minItems and
   maxItems qualities.  Therefore, they can be seen as a superset of
   sdfObject groups, additionally allowing for composition.

   As a result, an sdfThing directly or indirectly contains a set of
   sdfProperty, sdfAction, and sdfEvent definitions that describe the
   interaction affordances associated with some scope of functionality.

   A definition in an sdfThing group can refine the metadata of the
   definitions it is composed of: other definitions in sdfThing groups
   or definitions in sdfObject groups.

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2.3.  Member names: Given Names and Quality Names

   SDF documents are JSON maps that mostly employ JSON maps as member
   values, which in turn mostly employ JSON maps as their member values,
   and so on.  This nested structure of JSON maps creates a tree, where
   the edges are the member names (map keys) used in these JSON maps.
   (In certain cases, where member names are not needed, JSON arrays may
   be interspersed in this tree.)

2.3.1.  Given Names and Quality Names

   For any particular JSON map in an SDF document, the set of member
   names that are used is either of:

   *  A set of "_Quality Names_", where the entries in the map are
      Qualities.  Quality Names are defined by the present specification
      and its extensions, together with specific semantics to be
      associated with the member value given with a certain Quality
      Name.

   *  A set of "_Given Names_", where the entries in the map are
      separate entities (definitions, declarations, etc.) that each have
      names that are chosen by the SDF document author in order that
      these names can be employed by a user of that model.

   In a path from the root of the tree to any leaf, Quality Names and
   Given Names roughly alternate (with the information block,
   Section 3.1, as a prominent exception).

   The meaning of the JSON map that is the member value associated with
   a Given Name is derived from the Quality Name that was used as the
   member name associated to the parent.  In the CDDL grammar given in
   Appendix A, JSON maps with member names that are Given Names are
   defined using the CDDL generic rule reference named<membervalues>,
   where membervalues is in turn the structure of the member values of
   the JSON map, i.e., the value of the member named by the Given Name.
   As quality-named maps and given-named maps roughly alternate in a
   path down the tree, membervalues is usually a map built from Quality
   Names as keys.

2.3.2.  Hierarchical Names

   From the outside of a specification, Given Names are usually used as
   part of a hierarchical name that looks like a JSON pointer [RFC6901],
   itself generally rooted in (used as the fragment identifier in) an
   outer namespace that looks like an https:// URL (see Section 4).

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   As Quality Names and Given Names roughly alternate in a path into the
   model, the JSON pointer part of the hierarchical name also alternates
   between Quality Names and Given Names.

2.3.3.  Extensibility of Given Names and Quality Names

   In SDF, both Quality Names and Given Names are _extension points_.
   This is more obvious for Quality Names: Extending SDF is mostly done
   by defining additional qualities.  To enable non-conflicting third
   party extensions to SDF, qualified names (names with an embedded
   colon) can be used as Quality Names.

   A nonqualified Quality Name is composed of ASCII letters, digits, and
   $ signs, starting with a lower case letter or a $ sign (i.e., using a
   pattern of "[a-z$][A-Za-z$0-9]*").  Names with $ signs are intended
   to be used for functions separate from most other names; for
   instance, in this specification $comment is used for the comment
   quality (the presence or absence of a $comment quality does not
   change the meaning of the SDF model).  Names that are composed of
   multiple English words can use the "lowerCamelCase" convention
   [CamelCase] for indicating the word boundaries; no other use is
   intended for upper case letters in quality names.

   A qualified Quality Name is composed of a Quality Name Prefix, a :
   (colon) character, and a nonqualified Quality Name.  Quality Name
   Prefixes are registered in the "Quality Name Prefixes" sub-registry
   in the "SDF Parameters" registry (Section 7.4.1); they are composed
   of lower case ASCII letters and digits, starting with a lower case
   ASCII letter (i.e., using a pattern of "[a-z][a-z0-9]*").

   Given Names are not restricted by the formal SDF syntax.  To enable
   non-surprising name translations in tools, combinations of ASCII
   alphanumeric characters and - (ASCII hyphen/minus) are preferred,
   typically employing KebabCase for names constructed out of multiple
   words [KebabCase].  ASCII hyphen/minus can then unambiguously be
   translated to an ASCII _ underscore character and back depending on
   the programming environment.  Some styles also allow a dot . in given
   names.  Given Names are often sufficiently self-explanatory that they
   can be used in place of the label quality if that is not given.  In
   turn, if a given name turns out too complicated, a more elaborate
   label can be given and the given name kept simple.  Base SDF does not
   address internationalization of given names.

   Further, to enable Given Names to have a more powerful role in
   building global hierarchical names, an extension is planned that
   makes use of qualified names for Given Names.  So, until that
   extension is defined, Given Names with (one or more) embedded colons
   are reserved and MUST NOT be used in an SDF document.

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   All names in SDF are case-sensitive.

3.  SDF structure

   SDF definitions are contained in SDF documents, together with data
   about the SDF document itself (information block).  Definitions and
   declarations from additional SDF documents can be referenced;
   together with the definitions and declarations in the referencing SDF
   document they build the SDF model expressed by that SDF document.

   Each SDF document is represented as a single JSON map.  This map has
   three blocks: the information block, the namespaces block, and the
   definitions block.

3.1.  Information block

   The information block contains generic meta data for the SDF document
   itself and all included definitions.  To enable tool integration, the
   information block is optional in the grammar of SDF; most processes
   for working with SDF documents will have policies that only SDF
   documents with an info block can be processed.  It is therefore
   RECOMMENDED that SDF validator tools emit a warning when no
   information block is found.

   The keyword (map key) that defines an information block is "info".
   Its value is a JSON map in turn, with a set of entries that represent
   qualities that apply to the included definition.

   Qualities of the information block are shown in Table 1.

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      +=============+=========+==========+==========================+
      | Quality     | Type    | Required | Description              |
      +=============+=========+==========+==========================+
      | title       | string  | no       | A short summary to be    |
      |             |         |          | displayed in search      |
      |             |         |          | results, etc.            |
      +-------------+---------+----------+--------------------------+
      | description | string  | no       | Long-form text           |
      |             |         |          | description (no          |
      |             |         |          | constraints)             |
      +-------------+---------+----------+--------------------------+
      | version     | string  | no       | The incremental version  |
      |             |         |          | of the definition        |
      +-------------+---------+----------+--------------------------+
      | modified    | string  | no       | Time of the latest       |
      |             |         |          | modification             |
      +-------------+---------+----------+--------------------------+
      | copyright   | string  | no       | Link to text or embedded |
      |             |         |          | text containing a        |
      |             |         |          | copyright notice         |
      +-------------+---------+----------+--------------------------+
      | license     | string  | no       | Link to text or embedded |
      |             |         |          | text containing license  |
      |             |         |          | terms                    |
      +-------------+---------+----------+--------------------------+
      | features    | array   | no       | List of extension        |
      |             | of      |          | features used            |
      |             | strings |          |                          |
      +-------------+---------+----------+--------------------------+
      | $comment    | string  | no       | Source code comments     |
      |             |         |          | only, no semantics       |
      +-------------+---------+----------+--------------------------+

                Table 1: Qualities of the Information Block

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   The version quality is used to indicate version information about the
   set of definitions in the SDF document.  The version is RECOMMENDED
   to be lexicographically increasing over the life of a model: a newer
   model always has a version string that string-compares higher than
   all previous versions.  This is easily achieved by following the
   convention to start the version with an [RFC3339] date-time or, if
   new versions are generated less frequently than once a day, just the
   full-date (i.e., YYYY-MM-DD); in many cases, that will be all that is
   needed (see Figure 1 for an example).  This specification does not
   give a strict definition for the format of the version string but
   each using system or organization should define internal structure
   and semantics to the level needed for their use.  If no further
   details are provided, a date-time or full-date in this field can be
   assumed to indicate the latest update time of the definitions in the
   SDF document.

   The modified quality can be used with a value using [RFC3339] date-
   time (with Z for time-zone) or full-date format to express time of
   the latest revision of the definitions.

   The license string is preferably either a URI that points to a web
   page with an unambiguous definition of the license, or an [SPDX]
   license identifier.  (As an example, for models to be handled by the
   One Data Model liaison group, this license identifier will typically
   be "BSD-3-Clause".)

   The features quality can be used to list names of critical (i.e.,
   cannot be safely ignored) SDF extension features that need to be
   understood for the definitions to be properly processed.  Extension
   feature names will be specified in extension documents.

3.2.  Namespaces block

   The namespaces block contains the namespace map and the
   defaultNamespace setting.

   The namespace map is a map from short names for URIs to the namespace
   URIs themselves.

   The defaultNamespace setting selects one of the entries in the
   namespace map by giving its short name.  The associated URI (value of
   this entry) becomes the default namespace for the SDF document.

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     +==================+========+==========+=======================+
     | Quality          | Type   | Required | Description           |
     +==================+========+==========+=======================+
     | namespace        | map    | no       | Defines short names   |
     |                  |        |          | mapped to namespace   |
     |                  |        |          | URIs, to be used as   |
     |                  |        |          | identifier prefixes   |
     +------------------+--------+----------+-----------------------+
     | defaultNamespace | string | no       | Identifies one of the |
     |                  |        |          | prefixes in the       |
     |                  |        |          | namespace map to be   |
     |                  |        |          | used as a default in  |
     |                  |        |          | resolving identifiers |
     +------------------+--------+----------+-----------------------+

                        Table 2: Namespaces Block

   The following example declares a set of namespaces and defines cap as
   the default namespace.  By convention, the values in the namespace
   map contain full URIs without a fragment identifier, and the fragment
   identifier is then added, if needed, where the namespace entry is
   used.

   "namespace": {
     "cap": "https://example.com/capability/cap",
     "zcl": "https://zcl.example.com/sdf"
   },
   "defaultNamespace": "cap"

   If no defaultNamespace setting is given, the SDF document does not
   contribute to a global namespace (all definitions remain local to the
   model and are not accessible for re-use by other models).  As the
   defaultNamespace is set by giving a namespace short name, its
   presence requires a namespace map that contains a mapping for that
   namespace short name.

   If no namespace map is given, no short names for namespace URIs are
   set up, and no defaultNamespace can be given.

3.3.  Definitions block

   The Definitions block contains one or more groups, each identified by
   a Class Name Keyword (there can only be one group per keyword; the
   actual grouping is just a shortcut and does not carry any specific
   semantics).  The value of each group is a JSON map, the keys of which
   serve for naming the individual definitions in this group, and the
   corresponding values provide a set of qualities (name-value pairs)
   for the individual definition.  (In short, we speak of the map

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   entries as "named sets of qualities".)

   Each group may contain zero or more definitions.  Each identifier
   defined creates a new type and term in the target namespace.
   Declarations have a scope of the definition block they are directly
   contained in.

   A definition may in turn contain other definitions.  Each definition
   is a named set of qualities, i.e., it consists of the newly defined
   identifier and a set of key-value pairs that represent the defined
   qualities and contained definitions.

   An example for an sdfObject definition is given in Figure 3:

   "sdfObject": {
     "foo": {
       "sdfProperty": {
         "bar": {
           "type": "boolean"
         }
       }
     }
   }

                   Figure 3: Example sdfObject definition

   This example defines an sdfObject "foo" that is defined in the
   default namespace (full address: #/sdfObject/foo), containing a
   property that can be addressed as #/sdfObject/foo/sdfProperty/bar,
   with data of type boolean.

   Often, definitions are also declarations: the definition of the entry
   "bar" in the property "foo" means that data corresponding to the
   "foo" property in a property interaction offered by Thing can have
   zero or one components modeled by "bar".  Entries within sdfProperty,
   sdfAction, and sdfEvent, within sdfObject or sdfThing entries, are
   declarations; entries within sdfData are not.  Similarly, sdfObject
   or sdfThing entries within an sdfThing definition specify that the
   interactions offered by a Thing modeled by this sdfThing include the
   interactions modeled by the nested sdfObject or sdfThing.

4.  Names and namespaces

   SDF documents may contribute to a global namespace, and may reference
   elements from that global namespace.  (An SDF document that does not
   set a defaultNamespace does not contribute to a global namespace.)

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4.1.  Structure

   Global names look exactly like https:// URIs with attached fragment
   identifiers.

   There is no intention to require that these URIs can be dereferenced.
   (However, as future extensions of SDF might find a use for
   dereferencing global names, the URI should be chosen in such a way
   that this may become possible in the future.  See also
   [I-D.bormann-t2trg-deref-id-01] for a discussion of dereferenceable
   identifiers.)

   The absolute URI of a global name should be a URI as per Section 3 of
   [RFC3986], with a scheme of "https" and a path (hier-part in
   [RFC3986]).  For base SDF, the query part should not be used (it
   might be used in extensions).

   The fragment identifier is constructed as per Section 6 of [RFC6901].

4.2.  Contributing global names

   The fragment identifier part of a global name defined in an SDF
   document is constructed from a JSON pointer that selects the element
   defined for this name in the SDF document.

   The absolute URI part is a copy of the default namespace, i.e., the
   default namespace is always the target namespace for a name for which
   a definition is contributed.  When emphasizing that name definitions
   are contributed to the default namespace, we therefore also call it
   the "target namespace" of the SDF document.

   For instance, in Figure 1, definitions for the following global names
   are contributed:

   *  https://example.com/capability/cap#/sdfObject/Switch

   *  https://example.com/capability/cap#/sdfObject/Switch/sdfProperty/
      value

   *  https://example.com/capability/cap#/sdfObject/Switch/sdfAction/on

   *  https://example.com/capability/cap#/sdfObject/Switch/sdfAction/off

   Note the #, which separates the absolute-URI part (Section 4.3 of
   [RFC3986]) from the fragment identifier part.

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4.3.  Referencing global names

   A name reference takes the form of the production curie in
   [W3C.NOTE-curie-20101216] (note that this excludes the production
   safe-curie), but also limiting the IRIs involved in that production
   to URIs as per [RFC3986] and the prefixes to ASCII characters
   [RFC0020].

   A name that is contributed by the current SDF document can be
   referenced by a Same-Document Reference as per Section 4.4 of
   [RFC3986].  As there is little point in referencing the entire SDF
   document, this will be a # followed by a JSON pointer.  This is the
   only kind of name reference to itself that is possible in an SDF
   document that does not set a default namespace.

   Name references that point outside the current SDF document need to
   contain curie prefixes.  These then reference namespace declarations
   in the namespaces block.

   For example, if a namespace prefix is defined:

   "namespace": {
     "foo": "https://example.com/"
   }

   Then this reference to that namespace:

   "sdfRef": "foo:#/sdfData/temperatureData"

   references the global name:

   "https://example.com/#/sdfData/temperatureData"

   Note that there is no way to provide a URI scheme name in a curie, so
   all references outside of the document need to go through the
   namespace map.

   Name references occur only in specific elements of the syntax of SDF:

   *  copying elements via sdfRef values

   *  pointing to elements via sdfRequired value elements

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4.4.  sdfRef

   In a JSON map establishing a definition, the keyword "sdfRef" is used
   to copy all of the qualities and enclosed definitions of the
   referenced definition, indicated by the included name reference, into
   the newly formed definition.  (This can be compared to the processing
   of the "$ref" keyword in [JSO7].)

   For example, this reference:

   "temperatureProperty": {
     "sdfRef": "#/sdfData/temperatureData"
   }

   creates a new definition "temperatureProperty" that contains all of
   the qualities defined in the definition at /sdfData/temperatureData.

   The sdfRef member need not be the only member of a map.  Additional
   members may be present with the intention to override parts of the
   referenced map or to add new qualities or definitions.

   When processing sdfRef, if the target definition contains also sdfRef
   (i.e., is based on yet another definition), that MUST be processed as
   well.

   More formally, for a JSON map that contains an sdfRef member, the
   semantics is defined to be as if the following steps were performed:

   1.  The JSON map that contains the sdfRef member is copied into a
       variable named "patch".

   2.  The sdfRef member of the copy in "patch" is removed.

   3.  the JSON pointer that is the value of the sdfRef member is
       dereferenced and the result is copied into a variable named
       "original".

   4.  The JSON Merge Patch algorithm [RFC7396] is applied to patch the
       contents of "original" with the contents of "patch".

   5.  The result of the Merge Patch is used in place of the value of
       the original JSON map.

   Note that the formal syntaxes given in Appendices A and B generally
   describe the _result_ of applying a merge-patch; the notations are
   not powerful enough to describe, for instance, the effect of null
   values given with the sdfRef to remove members of JSON maps from the
   referenced target.  Nonetheless, the syntaxes also give the syntax of

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   the sdfRef itself, which vanishes during the resolution; in many
   cases therefore even merge-patch inputs will validate with these
   formal syntaxes.

   Given the example (Figure 1), and the following definition:

   {
     "info": {
       "title": "Example light switch using sdfRef"
     },
     "namespace": {
       "cap": "https://example.com/capability/cap"
     },
     "defaultNamespace": "cap",
     "sdfObject": {
       "BasicSwitch": {
         "sdfRef": "cap:#/sdfObject/Switch",
         "sdfAction": {
           "toggle": null
         }
       }
     }
   }

   The resulting definition of the "BasicSwitch" sdfObject would be
   identical to the definition of the "Switch" sdfObject except it would
   not contain the "toggle" Action.

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   {
     "info": {
       "title": "Example light switch using sdfRef"
     },
     "namespace": {
       "cap": "https://example.com/capability/cap"
     },
     "defaultNamespace": "cap",
     "sdfObject": {
       "BasicSwitch": {
         "sdfProperty": {
           "value": {
             "description":
   "The state of the switch; false for off and true for on.",
             "type": "boolean"
           }
         },
         "sdfAction": {
           "on": {
             "description":
   "Turn the switch on; equivalent to setting value to true."
           },
           "off": {
             "description":
   "Turn the switch off; equivalent to setting value to false."
           }
         }
       }
     }
   }

4.4.1.  Resolved models

   A model where all sdfRef references are processed as described in
   Section 4.4 is called a resolved model.

   For example, given the following sdfData definitions:

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   "sdfData": {
     "Coordinate" : {
       "type": "number", "unit": "m"
     },
     "X-Coordinate" : {
       "sdfRef" : "#/sdfData/Coordinate",
       "description":
   "Distance from the base of the Thing along the X axis."
     },
     "Non-neg-X-Coordinate" : {
       "sdfRef": "#/sdfData/X-Coordinate",
       "minimum": 0
     }
   }

   After resolving the definitions would look as follows:

   "sdfData": {
     "Coordinate" : {
       "type": "number", "unit": "m"
     },
     "X-Coordinate" : {
       "description":
   "Distance from the base of the Thing along the X axis.",
       "type": "number", "unit": "m"
     },
     "Non-neg-X-Coordinate" : {
       "description":
   "Distance from the base of the Thing along the X axis.",
       "minimum": 0, "type": "number", "unit": "m"
     }
   }

4.5.  sdfRequired

   The keyword "sdfRequired" is provided to apply a constraint that
   defines for which declarations the corresponding data are mandatory
   in a Thing modeled by the current definition.

   The value of "sdfRequired" is an array of references, each indicating
   one or more declarations that are mandatory to be represented.

   References in this array can be SDF names (JSON Pointers), or one of
   two abbreviated reference formats:

   *  a text string with an affordance name or grouping name.  All
      affordance declarations that are directly (i.e., not nested
      further in another grouping) in the same grouping and that carry

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      this name (there can be multiple ones, one per affordance type)
      are declared to be mandatory to be represented.  The same applies
      for groupings made mandatory within groupings containing them.

   *  the Boolean value true.  The affordance/grouping itself that
      carries the sdfRequired keyword is declared to be mandatory to be
      represented.

   The example in Figure 4 shows two required elements in the sdfObject
   definition for "temperatureWithAlarm", the sdfProperty
   "currentTemperature", and the sdfEvent "overTemperatureEvent".  The
   example also shows the use of JSON pointer with "sdfRef" to use a
   pre-existing definition in this definition, for the "alarmType" data
   (sdfOutputData) produced by the sdfEvent "overTemperatureEvent".

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   "sdfObject": {
     "temperatureWithAlarm": {
       "sdfRequired": [
   "#/sdfObject/temperatureWithAlarm/sdfProperty/currentTemperature",
   "#/sdfObject/temperatureWithAlarm/sdfEvent/overTemperatureEvent"
       ],
       "sdfData":{
          "temperatureData": {
           "type": "number"
         }
       },
       "sdfProperty": {
         "currentTemperature": {
   "sdfRef": "#/sdfObject/temperatureWithAlarm/sdfData/temperatureData"
         }
       },
       "sdfEvent": {
         "overTemperatureEvent": {
          "sdfOutputData": {
             "type": "object",
             "properties": {
               "alarmType": {
                 "sdfRef": "cap:#/sdfData/alarmTypes/quantityAlarms",
                 "const": "OverTemperatureAlarm"
               },
               "temperature": {
   "sdfRef": "#/sdfObject/temperatureWithAlarm/sdfData/temperatureData"
               }
             }
           }
         }
       }
     }
   }

                        Figure 4: Using sdfRequired

   In Figure 4, the same sdfRequired can also be represented in short
   form:

       "sdfRequired": ["currentTemperature", "overTemperatureEvent"]

   Or, for instance "overTemperatureEvent" could carry

         "overTemperatureEvent": {
           "sdfRequired": [true],
           "...": "..."
         }

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4.6.  Common Qualities

   Definitions in SDF share a number of qualities that provide metadata
   for them.  These are listed in Table 3.  None of these qualities are
   required or have default values that are assumed if the quality is
   absent.  If a label is required for an application and no label is
   given in the SDF model, the last part (reference-token, Section 3 of
   [RFC6901]) of the JSON pointer to the definition can be used.

       +=============+==============+=============================+
       | Quality     | Type         | Description                 |
       +=============+==============+=============================+
       | description | string       | long text (no constraints)  |
       +-------------+--------------+-----------------------------+
       | label       | string       | short text (no constraints) |
       +-------------+--------------+-----------------------------+
       | $comment    | string       | source code comments only,  |
       |             |              | no semantics                |
       +-------------+--------------+-----------------------------+
       | sdfRef      | sdf-pointer  | (see Section 4.4)           |
       +-------------+--------------+-----------------------------+
       | sdfRequired | pointer-list | (see Section 4.5, used in   |
       |             |              | affordances or groupings)   |
       +-------------+--------------+-----------------------------+

                        Table 3: Common Qualities

4.7.  Data Qualities

   Data qualities are used in sdfData and sdfProperty definitions, which
   are named sets of data qualities (abbreviated as named-sdq).

   Appendix C lists data qualities inspired by the various proposals at
   json-schema.org; the intention is that these (information model
   level) qualities are compatible with the (data model) semantics from
   the versions of the json-schema.org proposal they were imported from.

   Table 4 lists data qualities defined specifically for the present
   specification.

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     +===============+================+====================+=========+
     | Quality       | Type           | Description        | Default |
     +===============+================+====================+=========+
     | (common)      |                | Section 4.6        |         |
     +---------------+----------------+--------------------+---------+
     | unit          | string         | unit name (note 1) | N/A     |
     +---------------+----------------+--------------------+---------+
     | nullable      | boolean        | indicates a null   | true    |
     |               |                | value is available |         |
     |               |                | for this type      |         |
     +---------------+----------------+--------------------+---------+
     | contentFormat | string         | content type (IANA | N/A     |
     |               |                | media type string  |         |
     |               |                | plus parameters),  |         |
     |               |                | encoding (note 2)  |         |
     +---------------+----------------+--------------------+---------+
     | sdfType       | string         | sdfType            | N/A     |
     |               | (Section       | enumeration        |         |
     |               | 4.7.1)         | (extensible)       |         |
     +---------------+----------------+--------------------+---------+
     | sdfChoice     | named set of   | named alternatives | N/A     |
     |               | data qualities |                    |         |
     |               | (Section       |                    |         |
     |               | 4.7.2)         |                    |         |
     +---------------+----------------+--------------------+---------+
     | enum          | array of       | abbreviation for   | N/A     |
     |               | strings        | string-valued      |         |
     |               |                | named alternatives |         |
     +---------------+----------------+--------------------+---------+

                 Table 4: SDF-defined Qualities of sdfData

   1.  Note that the quality unit was called units in earlier drafts of
       SDF.  The unit name SHOULD be as per the SenML Units Registry or
       the Secondary Units Registry in [IANA.senml] as specified by
       Sections 4.5.1 and 12.1 of [RFC8428] and Section 3 of [RFC8798],
       respectively.

       Exceptionally, if a registration in these registries cannot be
       obtained or would be inappropriate, the unit name can also be a
       URI that is pointing to a definition of the unit.  Note that SDF
       processors are not expected to (and normally SHOULD NOT)
       dereference these URIs (see also
       [I-D.bormann-t2trg-deref-id-01]); they may be useful to humans,
       though.  A URI unit name is distinguished from a registered unit
       name by the presence of a colon; any registered unit names that
       contain a colon (at the time of writing, none) can therefore not
       be used in SDF.

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       For use by translators into ecosystems that require URIs for unit
       names, the URN sub-namespace "urn:ietf:params:unit" is provided
       (Section 7.3); URNs from this sub-namespace MUST NOT be used in a
       unit quality, in favor of simply notating the unit name (such as
       kg instead of urn:ietf:params:unit:kg).

   2.  The contentFormat quality follows the Content-Format-Spec as
       defined in Section 6 of [RFC9193], allowing for expressing both
       numeric and string based Content-Formats.

4.7.1.  sdfType

   SDF defines a number of basic types beyond those provided by JSON or
   JSO.  These types are identified by the sdfType quality, which is a
   text string from a set of type names defined by the "sdfType values"
   sub-registry in the "SDF Parameters" registry (Section 7.4.2).  The
   sdfType name is composed of lower case ASCII letters, digits, and -
   (ASCII hyphen/minus) characters, starting with a lower case ASCII
   letter (i.e., using a pattern of "[a-z][-a-z0-9]*"), typically
   employing KebabCase for names constructed out of multiple words
   [KebabCase].

   To aid interworking with JSO implementations, it is RECOMMENDED that
   sdfType is always used in conjunction with the type quality inherited
   from [JSO7V], in such a way as to yield a common representation of
   the type's values in JSON.

   Values for sdfType that are defined in this specification are shown
   in Table 5.  This table also gives a description of the semantics of
   the sdfType, the conventional value for type to be used with the
   sdfType value, and a conventional JSON representation for values of
   the type.

     +=============+=============+========+==========================+
     | sdfType     | Description | type   | JSON Representation      |
     +=============+=============+========+==========================+
     | byte-string | A sequence  | string | base64url without        |
     |             | of zero or  |        | padding (Section 3.4.5.2 |
     |             | more bytes  |        | of [RFC8949])            |
     +-------------+-------------+--------+--------------------------+
     | unix-time   | A point in  | number | POSIX time               |
     |             | civil time  |        | (Section 3.4.2 of        |
     |             | (note 1)    |        | [RFC8949])               |
     +-------------+-------------+--------+--------------------------+

        Table 5: Values defined in base SDF for the sdfType quality

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   (1) Note that the definition of unix-time does not imply the
   capability to represent points in time that fall on leap seconds.
   More date/time-related sdfTypes are likely to be added in the sdfType
   value registry.

   (In earlier drafts of this specification, a similar concept was
   called subtype.)

4.7.2.  sdfChoice

   Data can be a choice of named alternatives, called sdfChoice.  Each
   alternative is identified by a name (string, key in the outer JSON
   map used to represent the overall choice) and a set of dataqualities
   (each in an inner JSON map, the value used to represent the
   individual alternative in the outer JSON map).  Dataqualities that
   are specified at the same level as the sdfChoice apply to all choices
   in the sdfChoice, except those specific choices where the dataquality
   is overridden at the choice level.

   sdfChoice merges the functions of two constructs found in [JSO7V]:

   *  enum

      What would have been

      "enum": ["foo", "bar", "baz"]

      in earlier drafts of this specification, is often best represented
      as:

      "sdfChoice": {
        "foo": { "description": "This is a foonly"},
        "bar": { "description":
      "As defined in the second world congress"},
        "baz": { "description": "From zigbee foobaz"}
      }

      This allows the placement of other dataqualities such as
      description in the example.

      If an enum needs to use a data type different from text string,
      what would for instance have been:

      "type": "number",
      "enum": [1, 2, 3]

      in earlier drafts of this specification, is represented as:

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      "type": "number",
      "sdfChoice": {
        "a-better-name-for-alternative-1": { "const": 1 },
        "alternative-2": { "const": 2 },
        "the-third-alternative": { "const": 3 }
      }

      where the string names obviously would be chosen in a way that is
      descriptive for what these numbers actually stand for; sdfChoice
      also makes it easy to add number ranges into the mix.

      (Note that const can also be used for strings as in the previous
      example, for instance, if the actual string value is indeed a
      crucial element for the data model.)

   *  anyOf

      JSO provides a type union called anyOf, which provides a choice
      between anonymous alternatives.

      What could have been in JSO:

      "anyOf": [
        {"type": "array", "minItems": 3, "maxItems": "3",
         "items": {"$ref": "#/sdfData/rgbVal"}},
        {"type": "array", "minItems": 4, "maxItems": "4",
         "items": {"$ref": "#/sdfData/cmykVal"}}
      ]

      can be more descriptively notated in SDF as:

      "sdfChoice": {
        "rgb": {"type": "array", "minItems": 3, "maxItems": "3",
                "items": {"sdfRef": "#/sdfData/rgbVal"}},
        "cmyk": {"type": "array", "minItems": 4, "maxItems": "4",
                 "items": {"sdfRef": "#/sdfData/cmykVal"}}
      }

   Note that there is no need in SDF for the type intersection construct
   allOf or the peculiar type-xor construct oneOf found in [JSO7V].

   As a simplification for users of SDF models who are accustomed to the
   JSO enum keyword, this is retained, but limited to a choice of text
   string values, such that

   "enum": ["foo", "bar", "baz"]

   is syntactic sugar for

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   "sdfChoice": {
     "foo": { "const": "foo"},
     "bar": { "const": "bar"},
     "baz": { "const": "baz"}
   }

   In a single definition, the keyword enum cannot be used at the same
   time as the keyword sdfChoice, as the former is just syntactic sugar
   for the latter.

5.  Keywords for definition groups

   The following SDF keywords are used to create definition groups in
   the target namespace.  All these definitions share some common
   qualities as discussed in Section 4.6.

5.1.  sdfObject

   The sdfObject keyword denotes a group of zero or more sdfObject
   definitions. sdfObject definitions may contain or include definitions
   of Properties, Actions, Events declared for the sdfObject, as well as
   data types (sdfData group) to be used in this or other sdfObjects.

   The qualities of an sdfObject include the common qualities,
   additional qualities are shown in Table 6.  None of these qualities
   are required or have default values that are assumed if the quality
   is absent.

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       +=============+===========+================================+
       | Quality     | Type      | Description                    |
       +=============+===========+================================+
       | (common)    |           | Section 4.6                    |
       +-------------+-----------+--------------------------------+
       | sdfProperty | property  | zero or more named property    |
       |             |           | definitions for this sdfObject |
       +-------------+-----------+--------------------------------+
       | sdfAction   | action    | zero or more named action      |
       |             |           | definitions for this sdfObject |
       +-------------+-----------+--------------------------------+
       | sdfEvent    | event     | zero or more named event       |
       |             |           | definitions for this sdfObject |
       +-------------+-----------+--------------------------------+
       | sdfData     | named-sdq | zero or more named data type   |
       |             |           | definitions that might be used |
       |             |           | in the above                   |
       +-------------+-----------+--------------------------------+
       | minItems    | number    | (array) Minimum number of      |
       |             |           | multiplied affordances in      |
       |             |           | array                          |
       +-------------+-----------+--------------------------------+
       | maxItems    | number    | (array) Maximum number of      |
       |             |           | multiplied affordances in      |
       |             |           | array                          |
       +-------------+-----------+--------------------------------+

                     Table 6: Qualities of sdfObject

5.2.  sdfProperty

   The sdfProperty keyword denotes a group of zero or more Property
   definitions.

   Properties are used to model elements of state.

   The qualities of a Property definition include the data qualities
   (and thus the common qualities), see Section 4.7, additional
   qualities are shown in Table 7.

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    +============+=========+===============================+=========+
    | Quality    | Type    | Description                   | Default |
    +============+=========+===============================+=========+
    | (data)     |         | Section 4.7                   |         |
    +------------+---------+-------------------------------+---------+
    | readable   | boolean | Reads are allowed             | true    |
    +------------+---------+-------------------------------+---------+
    | writable   | boolean | Writes are allowed            | true    |
    +------------+---------+-------------------------------+---------+
    | observable | boolean | flag to indicate asynchronous | true    |
    |            |         | notification is available     |         |
    +------------+---------+-------------------------------+---------+

                    Table 7: Qualities of sdfProperty

5.3.  sdfAction

   The sdfAction keyword denotes a group of zero or more Action
   definitions.

   Actions are used to model commands and methods which are invoked.
   Actions have parameter data that are supplied upon invocation.

   The qualities of an Action definition include the common qualities,
   additional qualities are shown in Table 8.

        +===============+===========+============================+
        | Quality       | Type      | Description                |
        +===============+===========+============================+
        | (common)      |           | Section 4.6                |
        +---------------+-----------+----------------------------+
        | sdfInputData  | map       | data qualities of the      |
        |               |           | input data for an Action   |
        +---------------+-----------+----------------------------+
        | sdfOutputData | map       | data qualities of the      |
        |               |           | output data for an Action  |
        +---------------+-----------+----------------------------+
        | sdfData       | named-sdq | zero or more named data    |
        |               |           | type definitions that      |
        |               |           | might be used in the above |
        +---------------+-----------+----------------------------+

                     Table 8: Qualities of sdfAction

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   sdfInputData defines the input data of the action.  sdfOutputData
   defines the output data of the action.  As discussed in
   Section 2.2.3, a set of data qualities with type "object" can be used
   to substructure either data item, with optionality indicated by the
   data quality required.

5.4.  sdfEvent

   The sdfEvent keyword denotes zero or more Event definitions.

   Events are used to model asynchronous occurrences that may be
   communicated proactively.  Events have data elements which are
   communicated upon the occurrence of the event.

   The qualities of sdfEvent include the common qualities, additional
   qualities are shown in Table 9.

        +===============+===========+============================+
        | Quality       | Type      | Description                |
        +===============+===========+============================+
        | (common)      |           | Section 4.6                |
        +---------------+-----------+----------------------------+
        | sdfOutputData | map       | data qualities of the      |
        |               |           | output data for an Event   |
        +---------------+-----------+----------------------------+
        | sdfData       | named-sdq | zero or more named data    |
        |               |           | type definitions that      |
        |               |           | might be used in the above |
        +---------------+-----------+----------------------------+

                      Table 9: Qualities of sdfEvent

   sdfOutputData defines the output data of the action.  As discussed in
   Section 2.2.4, a set of data qualities with type "object" can be used
   to substructure the output data item, with optionality indicated by
   the data quality required.

5.5.  sdfData

   The sdfData keyword denotes a group of zero or more named data type
   definitions (named-sdq).

   An sdfData definition provides a reusable semantic identifier for a
   type of data item and describes the constraints on the defined type.
   It is not itself a declaration, i.e., it does not cause any of these
   data items to be included in an affordance definition.

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   The qualities of sdfData include the data qualities (and thus the
   common qualities), see Section 4.7.

6.  High Level Composition

   The requirements for high level composition include the following:

   *  The ability to represent products, standardized product types, and
      modular products while maintaining the atomicity of sdfObjects.

   *  The ability to compose a reusable definition block from
      sdfObjects, for example a single plug unit of an outlet strip with
      on/off control, energy monitor, and optional dimmer sdfObjects,
      while retaining the atomicity of the individual sdfObjects.

   *  The ability to compose sdfObjects and other definition blocks into
      a higher level sdfThing that represents a product, while retaining
      the atomicity of sdfObjects.

   *  The ability to enrich and refine a base definition to have
      product-specific qualities and quality values, such as unit,
      range, and scale settings.

   *  The ability to reference items in one part of a complex definition
      from another part of the same definition, for example to summarize
      the energy readings from all plugs in an outlet strip.

6.1.  Paths in the model namespaces

   The model namespace is organized according to terms that are defined
   in the SDF documents that contribute to the namespace.  For example,
   definitions that originate from an organization or vendor are
   expected to be in a namespace that is specific to that organization
   or vendor.

   The structure of a path in a namespace is defined by the JSON
   Pointers to the definitions in the SDF documents in that namespace.
   For example, if there is an SDF document defining an sdfObject
   "Switch" with an action "on", then the reference to the action would
   be "ns:/sdfObject/Switch/sdfAction/on" where ns is the namespace
   prefix (short name for the namespace).

6.2.  Modular Composition

   Modular composition of definitions enables an existing definition
   (could be in the same or another SDF document) to become part of a
   new definition by including a reference to the existing definition
   within the model namespace.

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6.2.1.  Use of the "sdfRef" keyword to re-use a definition

   An existing definition may be used as a template for a new
   definition, that is, a new definition is created in the target
   namespace which uses the defined qualities of some existing
   definition.  This pattern will use the keyword "sdfRef" as a quality
   of a new definition with a value consisting of a reference to the
   existing definition that is to be used as a template.

   In the definition that uses "sdfRef", new qualities may be added and
   existing qualities from the referenced definition may be overridden.
   (Note that JSON maps do not have a defined order, so the SDF
   processor may see these overrides before seeing the sdfRef.)

   Note that if the referenced definition contains qualities or
   definitions that are not valid in the context where the sdfRef is
   used (for instance, if an sdfThing definition would be added in an
   sdfObject definition), the resulting model, when resolved, may be
   invalid.

   As a convention, overrides are intended to be used only for further
   restricting the set of data values, as shown in Figure 5: any value
   for a cable-length also is a valid value for a length, with the
   additional restriction that the length cannot be smaller than 5 cm.
   (This is labeled as a convention as it cannot be checked in the
   general case; a quality of implementation consideration for a tool
   might be to provide at least some form of checking.)  Note that a
   description is provided that overrides the description of the
   referenced definition; as this quality is intended for human
   consumption there is no conflict with the intended goal.

   "sdfData":
     "length" : {
       "type": "number",
       "minimum": 0,
       "unit": "m"
       "description": "There can be no negative lengths."
     }
   ...
     "cable-length" : {
       "sdfRef": "#/sdfData/length"
       "minimum": 5e-2,
       "description": "Cables must be at least 5 cm."
     }

                                  Figure 5

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6.3.  sdfThing

   An sdfThing is a set of declarations and qualities that may be part
   of a more complex model.  For example, the sdfObject declarations
   that make up the definition of a single socket of an outlet strip
   could be encapsulated in an sdfThing, which itself could be used in a
   declaration in the sdfThing definition for the outlet strip (see
   Figure 6 in Appendix D.1 for an example SDF model).

   sdfThing definitions carry semantic meaning, such as a defined
   refrigerator compartment and a defined freezer compartment, making up
   a combination refrigerator-freezer product.  An sdfThing may be
   composed of sdfObjects and other sdfThings.  It can also contain
   sdfData definitions, as well as declarations of interaction
   affordances itself, such as a status (on/off) for the refrigerator-
   freezer as a whole (see Figure 7 in Appendix D.2 for an example SDF
   model illustrating these aspects).

   The qualities of sdfThing are shown in Table 10.  Analogous to
   sdfObject, the presence of one or both of the optional qualities
   "minItems" and "maxItems" defines the sdfThing as an array.

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         +=============+===========+=============================+
         | Quality     | Type      | Description                 |
         +=============+===========+=============================+
         | (common)    |           | Section 4.6                 |
         +-------------+-----------+-----------------------------+
         | sdfThing    | thing     |                             |
         +-------------+-----------+-----------------------------+
         | sdfObject   | object    |                             |
         +-------------+-----------+-----------------------------+
         | sdfProperty | property  | zero or more named property |
         |             |           | definitions for this thing  |
         +-------------+-----------+-----------------------------+
         | sdfAction   | action    | zero or more named action   |
         |             |           | definitions for this thing  |
         +-------------+-----------+-----------------------------+
         | sdfEvent    | event     | zero or more named event    |
         |             |           | definitions for this thing  |
         +-------------+-----------+-----------------------------+
         | sdfData     | named-sdq | zero or more named data     |
         |             |           | type definitions that might |
         |             |           | be used in the above        |
         +-------------+-----------+-----------------------------+
         | minItems    | number    | (array) Minimum number of   |
         |             |           | multiplied affordances in   |
         |             |           | array                       |
         +-------------+-----------+-----------------------------+
         | maxItems    | number    | (array) Maximum number of   |
         |             |           | multiplied affordances in   |
         |             |           | array                       |
         +-------------+-----------+-----------------------------+

                      Table 10: Qualities of sdfThing

7.  IANA Considerations

   // RFC Ed.: throughout this section, please replace RFC XXXX with
   // this RFC number, and remove this note.

7.1.  Media Type

   IANA is requested to add the following Media-Type to the "Media
   Types" registry.

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   +==========+======================+=======================+
   | Name     | Template             | Reference             |
   +==========+======================+=======================+
   | sdf+json | application/sdf+json | RFC XXXX, Section 7.1 |
   +----------+----------------------+-----------------------+

            Table 11: Media Type Registration for SDF

   Type name:  application
   Subtype name:  sdf+json
   Required parameters:  none
   Optional parameters:  none
   Encoding considerations:  binary (JSON is UTF-8-encoded text)
   Security considerations:  Section 8 of RFC XXXX
   Interoperability considerations:  none
   Published specification:  Section 7.1 of RFC XXXX
   Applications that use this media type:  Tools for data and
      interaction modeling in the Internet of Things and related
      environments
   Fragment identifier considerations:  A JSON Pointer fragment
      identifier may be used, as defined in Section 6 of [RFC6901].
   Additional information:  Magic number(s):  n/a

                            File extension(s):  .sdf.json

                            Windows Clipboard Name:  "Semantic
         Definition Format (SDF) for Data and Interactions of Things"

                            Macintosh file type code(s):  n/a

                            Macintosh Universal Type Identifier code:  o
         rg.ietf.sdf-json
         conforms to public.text
   Person & email address to contact for further information:  ASDF WG
      mailing list (asdf@ietf.org), or IETF Applications and Real-Time
      Area (art@ietf.org)
   Intended usage:  COMMON
   Restrictions on usage:  none
   Author/Change controller:  IETF
   Provisional registration:  no

7.2.  Content-Format

   This document adds the following Content-Format to the "CoAP Content-
   Formats", within the "Constrained RESTful Environments (CoRE)
   Parameters" registry, where TBD1 comes from the "IETF Review" 256-999
   range.

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   +======================+================+======+===========+
   | Content Type         | Content Coding | ID   | Reference |
   +======================+================+======+===========+
   | application/sdf+json | -              | TBD1 | RFC XXXX  |
   +----------------------+----------------+------+-----------+

            Table 12: SDF Content-format Registration

   // RFC Ed.: please replace TBD1 with the assigned ID, remove the
   requested range, and remove this note.
   // RFC Ed.: please replace RFC XXXX with this RFC number and remove
   this note.

7.3.  IETF URN Sub-namespace for Unit Names (urn:ietf:params:unit)

   IANA is requested to register the following value in the "IETF URN
   Sub-namespace for Registered Protocol Parameter Identifiers" registry
   in [IANA.params], following the template in [RFC3553]:

   Registry name:  unit

   Specification:  RFC XXXX

   Repository:  combining the symbol values from the SenML Units
      Registry and the Secondary Units Registry in [IANA.senml] as
      specified by Sections 4.5.1 and 12.1 of [RFC8428] and Section 3 of
      [RFC8798], respectively (which by the registration policy are
      guaranteed to be non-overlapping).

   Index value:  Percent-encoding (Section 2.1 of [RFC3986]) is required
      of any characters in unit names as required by ABNF rule "pchar"
      in Section 3.3 of [RFC3986], specifically at the time of writing
      for the unit names "%" (deprecated in favor of "/"), "%RH", "%EL".

7.4.  Registries

   IANA is requested to create an "SDF Parameters" registry, with the
   sub-registries defined in this Section.

7.4.1.  Quality Name Prefixes

   IANA is requested to create a "Quality Name Prefixes" sub-registry in
   the "SDF Parameters" registry, with the following template:

   Prefix:  A name composed of lower case ASCII letters and digits,
      starting with a lower case ASCII letter (i.e., using a pattern of
      "[a-z][a-z0-9]*").

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   Contact:  A contact point for the organization that assigns quality
      names with this prefix.

   Quality Name Prefixes are intended to be registered by organizations
   that intend to define quality names constructed with an organization-
   specifix prefix (Section 2.3.3).

   The registration policy is Expert Review as per Section 4.5 of
   [BCP26].  The instructions to the Expert are to ascertain that the
   organization will handle quality names constructed using their prefix
   in a way that roughly achieves the objectives for an IANA registry
   that support interoperability of SDF models employing these quality
   names, including:

   *  Stability, "stable and permanent";

   *  Transparency, "readily available", "in sufficient detail"
      (Section 4.6 of [BCP26]).

   The Expert will take into account that other organizations operate in
   different ways than the IETF, and that as a result some of these
   overall objectives will be achieved in a different way and to a
   different level of comfort.

   The "Quality Name Prefixes" sub-registry starts out empty.

7.4.2.  sdfType Values

   IANA is requested to create a "sdfType values" sub-registry in the
   "SDF Parameters" registry, with the following template:

   Name:  A name composed of lower case ASCII letters, digits and -
      (ASCII hyphen/minus) characters, starting with a lower case ASCII
      letter (i.e., using a pattern of "[a-z][-a-z0-9]*").

   Description:  A short description of the information model level
      structure and semantics

   type:  The value of the quality "type" to be used with this sdfType

   JSON Representation  A short description of a JSON representation
      that can be used for this sdfType.  This MUST be consistent with
      the type.

   Reference:  A more detailed specification of meaning and use of
      sdfType.

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   sdfType values are intended to be registered to enable modeling
   additional SDF-specific types (see Section 4.7.1).

   The registration policy is Specification Required as per Section 4.6
   of [BCP26].  The instructions to the Expert are to ascertain that the
   specification provides enough detail to enable interoperability
   between implementations of the sdfType being registered, and that
   names are chosen with enough specificity that ecosystem-specific
   sdfTypes will not be confused with more generally applicable ones.

   The initial set of registrations is described in Table 13.

   +=============+=============+========+================+============+
   | Name        | Description | type   | JSON           | Reference  |
   |             |             |        | Representation |            |
   +=============+=============+========+================+============+
   | byte-string | A sequence  | string | base64url      | Section    |
   |             | of zero or  |        | without        | 3.4.5.2 of |
   |             | more bytes  |        | padding        | [RFC8949]  |
   +-------------+-------------+--------+----------------+------------+
   | unix-time   | A point in  | number | POSIX time     | Section    |
   |             | civil time  |        |                | 3.4.2 of   |
   |             |             |        |                | [RFC8949]  |
   +-------------+-------------+--------+----------------+------------+

                 Table 13: Initial set of sdfType values

8.  Security Considerations

   Some wider issues are discussed in [RFC8576].

   (Specifics: TBD.)

9.  References

9.1.  Normative References

   [BCP26]    Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/rfc/rfc8126>.

   [IANA.params]
              IANA, "Uniform Resource Name (URN) Namespace for IETF
              Use", <https://www.iana.org/assignments/params>.

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   [IANA.senml]
              IANA, "Sensor Measurement Lists (SenML)",
              <https://www.iana.org/assignments/senml>.

   [RFC0020]  Cerf, V., "ASCII format for network interchange", STD 80,
              RFC 20, DOI 10.17487/RFC0020, October 1969,
              <https://www.rfc-editor.org/rfc/rfc20>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/rfc/rfc3339>.

   [RFC3553]  Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
              IETF URN Sub-namespace for Registered Protocol
              Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June
              2003, <https://www.rfc-editor.org/rfc/rfc3553>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/rfc/rfc3986>.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              DOI 10.17487/RFC4122, July 2005,
              <https://www.rfc-editor.org/rfc/rfc4122>.

   [RFC6901]  Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
              "JavaScript Object Notation (JSON) Pointer", RFC 6901,
              DOI 10.17487/RFC6901, April 2013,
              <https://www.rfc-editor.org/rfc/rfc6901>.

   [RFC7396]  Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396,
              DOI 10.17487/RFC7396, October 2014,
              <https://www.rfc-editor.org/rfc/rfc7396>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

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   [RFC8428]  Jennings, C., Shelby, Z., Arkko, J., Keranen, A., and C.
              Bormann, "Sensor Measurement Lists (SenML)", RFC 8428,
              DOI 10.17487/RFC8428, August 2018,
              <https://www.rfc-editor.org/rfc/rfc8428>.

   [RFC8610]  Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
              Definition Language (CDDL): A Notational Convention to
              Express Concise Binary Object Representation (CBOR) and
              JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
              June 2019, <https://www.rfc-editor.org/rfc/rfc8610>.

   [RFC8798]  Bormann, C., "Additional Units for Sensor Measurement
              Lists (SenML)", RFC 8798, DOI 10.17487/RFC8798, June 2020,
              <https://www.rfc-editor.org/rfc/rfc8798>.

   [RFC8949]  Bormann, C. and P. Hoffman, "Concise Binary Object
              Representation (CBOR)", STD 94, RFC 8949,
              DOI 10.17487/RFC8949, December 2020,
              <https://www.rfc-editor.org/rfc/rfc8949>.

   [RFC9165]  Bormann, C., "Additional Control Operators for the Concise
              Data Definition Language (CDDL)", RFC 9165,
              DOI 10.17487/RFC9165, December 2021,
              <https://www.rfc-editor.org/rfc/rfc9165>.

   [RFC9193]  Keränen, A. and C. Bormann, "Sensor Measurement Lists
              (SenML) Fields for Indicating Data Value Content-Format",
              RFC 9193, DOI 10.17487/RFC9193, June 2022,
              <https://www.rfc-editor.org/rfc/rfc9193>.

   [SPDX]     "SPDX License List", <https://spdx.org/licenses/>.

   [W3C.NOTE-curie-20101216]
              Birbeck, M., Ed. and S. McCarron, Ed., "CURIE Syntax 1.0",
              W3C NOTE NOTE-curie-20101216, W3C NOTE-curie-20101216, 16
              December 2010,
              <https://www.w3.org/TR/2010/NOTE-curie-20101216/>.

9.2.  Informative References

   [CamelCase]
              "Camel Case", December 2014,
              <http://wiki.c2.com/?CamelCase>.

   [ECMA-262] Ecma International, "ECMAScript 2020 Language
              Specification", ECMA Standard ECMA-262, 11th Edition, June
              2020, <https://www.ecma-international.org/wp-
              content/uploads/ECMA-262.pdf>.

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   [I-D.bormann-asdf-sdf-mapping]
              Bormann, C. and J. Romann, "Semantic Definition Format
              (SDF): Mapping files", Work in Progress, Internet-Draft,
              draft-bormann-asdf-sdf-mapping-02, 26 April 2023,
              <https://datatracker.ietf.org/doc/html/draft-bormann-asdf-
              sdf-mapping-02>.

   [I-D.bormann-asdf-sdftype-link]
              Bormann, C., "An sdfType for Links", Work in Progress,
              Internet-Draft, draft-bormann-asdf-sdftype-link-01, 3 June
              2023, <https://datatracker.ietf.org/doc/html/draft-
              bormann-asdf-sdftype-link-01>.

   [I-D.bormann-t2trg-deref-id-01]
              Bormann, C. and C. Amsüss, "The "dereferenceable
              identifier" pattern", Work in Progress, Internet-Draft,
              draft-bormann-t2trg-deref-id-01, 9 May 2023,
              <https://datatracker.ietf.org/doc/html/draft-bormann-
              t2trg-deref-id-01>.

   [I-D.irtf-t2trg-rest-iot]
              Keränen, A., Kovatsch, M., and K. Hartke, "Guidance on
              RESTful Design for Internet of Things Systems", Work in
              Progress, Internet-Draft, draft-irtf-t2trg-rest-iot-12, 25
              July 2023, <https://datatracker.ietf.org/doc/html/draft-
              irtf-t2trg-rest-iot-12>.

   [JSO4]     Galiegue, F., Zyp, K., and G. Court, "JSON Schema: core
              definitions and terminology", Work in Progress, Internet-
              Draft, draft-zyp-json-schema-04, 31 January 2013,
              <https://datatracker.ietf.org/doc/html/draft-zyp-json-
              schema-04>.  This is the base specification for json-
              schema.org "draft 4".

   [JSO4V]    Zyp, K. and G. Court, "JSON Schema: interactive and non
              interactive validation", Work in Progress, Internet-Draft,
              draft-fge-json-schema-validation-00, 31 January 2013,
              <https://datatracker.ietf.org/doc/html/draft-fge-json-
              schema-validation-00>.  This is the validation
              specification for json-schema.org "draft 4".

   [JSO7]     Wright, A. and H. Andrews, "JSON Schema: A Media Type for
              Describing JSON Documents", Work in Progress, Internet-
              Draft, draft-handrews-json-schema-01, 19 March 2018,
              <https://datatracker.ietf.org/doc/html/draft-handrews-
              json-schema-01>.  This is the base specification for json-
              schema.org "draft 7".

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   [JSO7V]    Wright, A., Andrews, H., and G. Luff, "JSON Schema
              Validation: A Vocabulary for Structural Validation of
              JSON", Work in Progress, Internet-Draft, draft-handrews-
              json-schema-validation-01, 19 March 2018,
              <https://datatracker.ietf.org/doc/html/draft-handrews-
              json-schema-validation-01>.  This is the validation
              specification for json-schema.org "draft 7".

   [KebabCase]
              "Kebab Case", August 2014,
              <http://wiki.c2.com/?KebabCase>.

   [OCF]      "OCF Resource Type Specification",
              <https://openconnectivity.org/specs/
              OCF_Resource_Type_Specification.pdf>.

   [OMA]      "OMA LightweightM2M (LwM2M) Object and Resource Registry",
              <http://www.openmobilealliance.org/wp/omna/lwm2m/
              lwm2mregistry.html>.

   [RFC8576]  Garcia-Morchon, O., Kumar, S., and M. Sethi, "Internet of
              Things (IoT) Security: State of the Art and Challenges",
              RFC 8576, DOI 10.17487/RFC8576, April 2019,
              <https://www.rfc-editor.org/rfc/rfc8576>.

   [RFC9485]  Bormann, C. and T. Bray, "I-Regexp: An Interoperable
              Regular Expression Format", RFC 9485,
              DOI 10.17487/RFC9485, October 2023,
              <https://www.rfc-editor.org/rfc/rfc9485>.

   [ZCL]      "The ZigBee Cluster Library", Elsevier, Zigbee Wireless
              Networking pp. 239-271,
              DOI 10.1016/b978-0-7506-8597-9.00006-9, 2008,
              <https://doi.org/10.1016/b978-0-7506-8597-9.00006-9>.

Appendix A.  Formal Syntax of SDF

   This appendix describes the syntax of SDF using CDDL [RFC8610].

   This appendix shows the framework syntax only, i.e., a syntax with
   liberal extension points.  Since this syntax is nearly useless in
   finding typos in an SDF specification, a second syntax, the
   validation syntax, is defined that does not include the extension
   points.  The validation syntax can be generated from the framework
   syntax by leaving out all lines containing the string EXTENSION-
   POINT; as this is trivial, the result is not shown here.

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   This appendix makes use of CDDL "features" as defined in Section 4 of
   [RFC9165].  Features whose names end in "-ext" indicate extension
   points for further evolution.

   start = sdf-syntax

   sdf-syntax = {
    ; info will be required in most process policies
    ? info: sdfinfo
    ? namespace: named<text>
    ? defaultNamespace: text
    ; Thing is a composition of objects that work together in some way
    ? sdfThing: named<thingqualities>
    ; Object is a set of Properties, Actions, and Events that together
    ; perform a particular function
    ? sdfObject: named<objectqualities>
    ; Includes Properties, Actions, and Events as well as sdfData
    paedataqualities
    EXTENSION-POINT<"top-ext">
   }

   sdfinfo = {
    ? title: text
    ? description: text
    ? version: text
    ? copyright: text
    ? license: text
    ? modified: modified-date-time
    ? features: [
                  * (any .feature "feature-name") ; EXTENSION-POINT
                ]
    optional-comment
    EXTENSION-POINT<"info-ext">
   }

   ; Shortcut for a map that gives names to instances of X
   ; (has keys of type text and values of type X)
   named<X> = { * text => X }

   ; EXTENSION-POINT is only used in framework syntax
   EXTENSION-POINT<f> = ( * (quality-name .feature f) => any )
   quality-name = text .regexp "([a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*"

   sdf-pointer = global / same-object / true
   global = text .regexp ".*[:#].*" ; rough CURIE or JSON Pointer syntax
   same-object = referenceable-name
   referenceable-name = text .regexp "[^:#]*"

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   ; per se no point in having an empty list, but used for sdfRequired
   ; in odmobject-multiple_axis_joystick.sdf.json
   pointer-list = [* sdf-pointer]

   optional-comment = (
    ? $comment: text       ; source code comments only, no semantics
   )

   commonqualities = (
    ? description: text    ; long text (no constraints)
    ? label: text          ; short text (no constraints); default to key
    optional-comment
    ? sdfRef: sdf-pointer
    ; applies to qualities of properties, of data:
    ? sdfRequired: pointer-list
   )

   arraydefinitionqualities = (
    ? "minItems" => uint
    ? "maxItems" => uint
   )

   paedataqualities = (
    ; Property represents the state of an instance of an object
    ? sdfProperty: named<propertyqualities>
    ; Action invokes an application layer verb associated with an object
    ? sdfAction: named<actionqualities>
    ; Event represents an occurrence of event associated with an object
    ? sdfEvent: named<eventqualities>
    ; Data represents a piece of information that can be the state of a
    ; property or a parameter to an action or a signal in an event
    ? sdfData: named<dataqualities>

   )

   ; for building hierarchy
   thingqualities = {
    commonqualities
    ? sdfObject: named<objectqualities>
    ? sdfThing: named<thingqualities>
    paedataqualities
    arraydefinitionqualities
    EXTENSION-POINT<"thing-ext">
   }

   ; for single objects, or for arrays of objects
   objectqualities = {
    commonqualities

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    paedataqualities
    arraydefinitionqualities
    EXTENSION-POINT<"object-ext">
   }

   parameter-list = dataqualities

   actionqualities = {
    commonqualities
    ? sdfInputData: parameter-list   ; sdfRequiredInputData applies here
    ? sdfOutputData: parameter-list  ; sdfRequired applies here
    ; zero or more named data type definitions that might be used above
    ? sdfData: named<dataqualities>
    EXTENSION-POINT<"action-ext">
   }

   eventqualities = {
    commonqualities
    ? sdfOutputData: parameter-list  ; sdfRequired applies here
    ; zero or more named data type definitions that might be used above
    ? sdfData: named<dataqualities>
    EXTENSION-POINT<"event-ext">
   }

   sdftype-name = text .regexp "[a-z][-a-z0-9]*"       ; EXTENSION-POINT

   dataqualities = {
    commonqualities
    jsonschema
    ? "unit" => text
    ? nullable: bool
    ? "sdfType" => "byte-string" / "unix-time"
               / (sdftype-name .feature "sdftype-ext") ; EXTENSION-POINT
    ? contentFormat: text
    EXTENSION-POINT<"data-ext">
   }

   propertyqualities = {
    ? observable: bool
    ? readable: bool
    ? writable: bool
    ~dataqualities
   }

   allowed-types = number / text / bool / null
                 / [* number] / [* text] / [* bool]
                 / {* text => any}
                 / (any .feature "allowed-ext")        ; EXTENSION-POINT

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   compound-type = (
     "type" => "object"
     ? required: [+text]
     ? properties: named<dataqualities>
   )

   optional-choice = (
    ? (("sdfChoice" => named<dataqualities>)
     // ("enum" => [+ text])) ; limited to text strings
   )

   jsonschema = (
    ? (("type" => "number" / "string" / "boolean" / "integer" / "array")
       // compound-type
       // (type: text .feature "type-ext")             ; EXTENSION-POINT
      )
    ; if present, all other qualities apply to all choices:
    optional-choice
    ; the next three should validate against type:
    ? const: allowed-types
    ? default: allowed-types
    ; number/integer constraints
    ? minimum: number
    ? maximum: number
    ? exclusiveMinimum: number
    ? exclusiveMaximum: number
    ? multipleOf: number                   ; ISSUE: Do we need this?
    ; text string constraints
    ? minLength: uint
    ? maxLength: uint
    ? pattern: text                ; regexp
    ? format: "date-time" / "date" / "time"
              / "uri" / "uri-reference" / "uuid"
              / (text .feature "format-ext")           ; EXTENSION-POINT
    ; array constraints
    ? minItems: uint
    ? maxItems: uint
    ? uniqueItems: bool
    ? items: jso-items
   )

   jso-items = {
        ? sdfRef: sdf-pointer ; import limited to subset allowed here...
        ? description: text   ; long text (no constraints)
        optional-comment
        ; leave commonqualities out for non-complex data types,
        ; but need the above three.
        ; no further nesting: no "array"

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        ? ((type: "number" / "string" / "boolean" / "integer")
           // compound-type
           // (type: text .feature "itemtype-ext")     ; EXTENSION-POINT
          )
        ; if present, all other qualities apply to all choices
        optional-choice
        ; jso subset
        ? minimum: number
        ? maximum: number
        ? format: text
        ? minLength: uint
        ? maxLength: uint
        EXTENSION-POINT<"items-ext">
      }

   modified-date-time = text .abnf modified-dt-abnf
   modified-dt-abnf = "modified-dt" .det rfc3339z

   ; RFC 3339 sans time-numoffset, slightly condensed
   rfc3339z = '
      date-fullyear   = 4DIGIT
      date-month      = 2DIGIT  ; 01-12
      date-mday       = 2DIGIT  ; 01-28, 01-29, 01-30, 01-31 based on
                                ; month/year
      time-hour       = 2DIGIT  ; 00-23
      time-minute     = 2DIGIT  ; 00-59
      time-second     = 2DIGIT  ; 00-58, 00-59, 00-60 based on leap sec
                                ; rules
      time-secfrac    = "." 1*DIGIT
      DIGIT           =  %x30-39 ; 0-9

      partial-time    = time-hour ":" time-minute ":" time-second
                        [time-secfrac]
      full-date       = date-fullyear "-" date-month "-" date-mday

      modified-dt     = full-date ["T" partial-time "Z"]
   '

Appendix B.  json-schema.org Rendition of SDF Syntax

   This appendix describes the syntax of SDF defined in Appendix A, but
   using a version of the description techniques advertised on json-
   schema.org [JSO7] [JSO7V].

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   The appendix shows both the validation and the framework syntax.
   Since most of the lines are the same between these two files, those
   lines are shown only once, with a leading space, in the form of a
   unified diff.  Lines leading with a - are part of the validation
   syntax, and lines leading with a + are part of the framework syntax.

    {
   -  "title": "sdf-validation.cddl -- Generated: 2023-11-04T15:25:34Z",
   +  "title": "sdf-framework.cddl -- Generated: 2023-11-04T15:25:46Z",
      "$schema": "http://json-schema.org/draft-07/schema#",
      "$ref": "#/definitions/sdf-syntax",
      "definitions": {
        "sdf-syntax": {
          "type": "object",
          "properties": {
            "info": {
              "$ref": "#/definitions/sdfinfo"
            },
            "namespace": {
              "type": "object",
              "additionalProperties": {
                "type": "string"
              }
            },
            "defaultNamespace": {
              "type": "string"
            },
            "sdfThing": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/thingqualities"
              }
            },
            "sdfObject": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/objectqualities"
              }
            },
            "sdfProperty": {
              "$ref": "#/definitions/sdfProperty-"
            },
            "sdfAction": {
              "$ref": "#/definitions/sdfAction-"
            },
            "sdfEvent": {
              "$ref": "#/definitions/sdfEvent-"
            },

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            "sdfData": {
              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
            }
          },
   +      "patternProperties": {
   +        "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +        }
   +      },
          "additionalProperties": false
        },
        "sdfinfo": {
          "type": "object",
          "properties": {
            "title": {
              "type": "string"
            },
            "description": {
              "type": "string"
            },
            "version": {
              "type": "string"
            },
            "copyright": {
              "type": "string"
            },
            "license": {
              "type": "string"
            },
            "modified": {
              "$ref": "#/definitions/modified-date-time"
            },
            "features": {
   -          "type": "array",
   -          "maxItems": 0
   +          "type": "array"
            },
            "$comment": {
              "type": "string"
            }
          },
   +      "patternProperties": {
   +        "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +        }
   +      },
          "additionalProperties": false
        },
        "modified-date-time": {
          "type": "string"

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        },
        "thingqualities": {
          "type": "object",
          "properties": {
            "description": {
              "type": "string"
            },
            "label": {
              "type": "string"
            },
            "$comment": {
              "type": "string"
            },
            "sdfRef": {
              "$ref": "#/definitions/sdf-pointer"
            },
            "sdfRequired": {
              "$ref": "#/definitions/pointer-list"
            },
            "sdfObject": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/objectqualities"
              }
            },
            "sdfThing": {
              "type": "object",
              "additionalProperties": {
                "$ref": "#/definitions/thingqualities"
              }
            },
            "sdfProperty": {
              "$ref": "#/definitions/sdfProperty-"
            },
            "sdfAction": {
              "$ref": "#/definitions/sdfAction-"
            },
            "sdfEvent": {
              "$ref": "#/definitions/sdfEvent-"
            },
            "sdfData": {
              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
            },
            "minItems": {
              "$ref": "#/definitions/uint"
            },
            "maxItems": {
              "$ref": "#/definitions/uint"

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            }
          },
   +      "patternProperties": {
   +        "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +        }
   +      },
          "additionalProperties": false
        },
        "sdf-pointer": {
          "anyOf": [
            {
              "$ref": "#/definitions/global"
            },
            {
              "$ref": "#/definitions/same-object"
            },
            {
              "$ref": "#/definitions/true"
            }
          ]
        },
        "global": {
          "type": "string",
          "pattern": "^[^\\n\\r]*[:#][^\\n\\r]*$"
        },
        "same-object": {
          "$ref": "#/definitions/referenceable-name"
        },
        "referenceable-name": {
          "type": "string",
          "pattern": "^[^:#]*$"
        },
        "true": {
          "type": "boolean",
          "const": true
        },
        "pointer-list": {
          "type": "array",
          "items": {
            "$ref": "#/definitions/sdf-pointer"
          }
        },
        "objectqualities": {
          "type": "object",
          "properties": {
            "description": {
              "type": "string"
            },

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            "label": {
              "type": "string"
            },
            "$comment": {
              "type": "string"
            },
            "sdfRef": {
              "$ref": "#/definitions/sdf-pointer"
            },
            "sdfRequired": {
              "$ref": "#/definitions/pointer-list"
            },
            "sdfProperty": {
              "$ref": "#/definitions/sdfProperty-"
            },
            "sdfAction": {
              "$ref": "#/definitions/sdfAction-"
            },
            "sdfEvent": {
              "$ref": "#/definitions/sdfEvent-"
            },
            "sdfData": {
              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
            },
            "minItems": {
              "$ref": "#/definitions/uint"
            },
            "maxItems": {
              "$ref": "#/definitions/uint"
            }
          },
   +      "patternProperties": {
   +        "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +        }
   +      },
          "additionalProperties": false
        },
        "propertyqualities": {
          "anyOf": [
            {
              "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },
              "properties": {
                "type": {
                  "$ref": "#/definitions/type-"

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                },
                "sdfChoice": {
                  "$ref": "#/definitions/sdfData-sdfChoice-properties-"
                },
                "observable": {
                  "type": "boolean"
                },
                "readable": {
                  "type": "boolean"
                },
                "writable": {
                  "type": "boolean"
                },
                "description": {
                  "type": "string"
                },
                "label": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "sdfRequired": {
                  "$ref": "#/definitions/pointer-list"
                },
                "const": {
                  "$ref": "#/definitions/allowed-types"
                },
                "default": {
                  "$ref": "#/definitions/allowed-types"
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "exclusiveMinimum": {
                  "type": "number"
                },
                "exclusiveMaximum": {
                  "type": "number"
                },
                "multipleOf": {
                  "type": "number"

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                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                },
                "pattern": {
                  "type": "string"
                },
                "format": {
                  "$ref": "#/definitions/format-"
                },
                "minItems": {
                  "$ref": "#/definitions/uint"
                },
                "maxItems": {
                  "$ref": "#/definitions/uint"
                },
                "uniqueItems": {
                  "type": "boolean"
                },
                "items": {
                  "$ref": "#/definitions/jso-items"
                },
                "unit": {
                  "type": "string"
                },
                "nullable": {
                  "type": "boolean"
                },
                "sdfType": {
                  "$ref": "#/definitions/sdfType-"
                },
                "contentFormat": {
                  "type": "string"
                }
              },
              "additionalProperties": false
            },
            {
              "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },
   +          "properties": {
   +            "type": {

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   +              "type": "string",
   +              "const": "object"
   +            },
   +            "required": {
   +              "type": "array",
   +              "items": {
   +                "type": "string"
   +              },
   +              "minItems": 1
   +            },
   +            "properties": {
   +              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
   +            },
   +            "sdfChoice": {
   +              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
   +            },
   +            "observable": {
   +              "type": "boolean"
   +            },
   +            "readable": {
   +              "type": "boolean"
   +            },
   +            "writable": {
   +              "type": "boolean"
   +            },
   +            "description": {
   +              "type": "string"
   +            },
   +            "label": {
   +              "type": "string"
   +            },
   +            "$comment": {
   +              "type": "string"
   +            },
   +            "sdfRef": {
   +              "$ref": "#/definitions/sdf-pointer"
   +            },
   +            "sdfRequired": {
   +              "$ref": "#/definitions/pointer-list"
   +            },
   +            "const": {
   +              "$ref": "#/definitions/allowed-types"
   +            },
   +            "default": {
   +              "$ref": "#/definitions/allowed-types"
   +            },
   +            "minimum": {
   +              "type": "number"

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   +            },
   +            "maximum": {
   +              "type": "number"
   +            },
   +            "exclusiveMinimum": {
   +              "type": "number"
   +            },
   +            "exclusiveMaximum": {
   +              "type": "number"
   +            },
   +            "multipleOf": {
   +              "type": "number"
   +            },
   +            "minLength": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "maxLength": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "pattern": {
   +              "type": "string"
   +            },
   +            "format": {
   +              "$ref": "#/definitions/format-"
   +            },
   +            "minItems": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "maxItems": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "uniqueItems": {
   +              "type": "boolean"
   +            },
   +            "items": {
   +              "$ref": "#/definitions/jso-items"
   +            },
   +            "unit": {
   +              "type": "string"
   +            },
   +            "nullable": {
   +              "type": "boolean"
   +            },
   +            "sdfType": {
   +              "$ref": "#/definitions/sdfType-"
   +            },
   +            "contentFormat": {
   +              "type": "string"

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   +            }
   +          },
   +          "additionalProperties": false
   +        },
   +        {
   +          "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },
   +          "properties": {
   +            "type": {
   +              "type": "string"
   +            },
   +            "sdfChoice": {
   +              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
   +            },
   +            "observable": {
   +              "type": "boolean"
   +            },
   +            "readable": {
   +              "type": "boolean"
   +            },
   +            "writable": {
   +              "type": "boolean"
   +            },
   +            "description": {
   +              "type": "string"
   +            },
   +            "label": {
   +              "type": "string"
   +            },
   +            "$comment": {
   +              "type": "string"
   +            },
   +            "sdfRef": {
   +              "$ref": "#/definitions/sdf-pointer"
   +            },
   +            "sdfRequired": {
   +              "$ref": "#/definitions/pointer-list"
   +            },
   +            "const": {
   +              "$ref": "#/definitions/allowed-types"
   +            },
   +            "default": {
   +              "$ref": "#/definitions/allowed-types"
   +            },
   +            "minimum": {

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   +              "type": "number"
   +            },
   +            "maximum": {
   +              "type": "number"
   +            },
   +            "exclusiveMinimum": {
   +              "type": "number"
   +            },
   +            "exclusiveMaximum": {
   +              "type": "number"
   +            },
   +            "multipleOf": {
   +              "type": "number"
   +            },
   +            "minLength": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "maxLength": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "pattern": {
   +              "type": "string"
   +            },
   +            "format": {
   +              "$ref": "#/definitions/format-"
   +            },
   +            "minItems": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "maxItems": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "uniqueItems": {
   +              "type": "boolean"
   +            },
   +            "items": {
   +              "$ref": "#/definitions/jso-items"
   +            },
   +            "unit": {
   +              "type": "string"
   +            },
   +            "nullable": {
   +              "type": "boolean"
   +            },
   +            "sdfType": {
   +              "$ref": "#/definitions/sdfType-"
   +            },
   +            "contentFormat": {

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   +              "type": "string"
   +            }
   +          },
   +          "additionalProperties": false
   +        },
   +        {
   +          "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },
   +          "properties": {
   +            "type": {
   +              "$ref": "#/definitions/type-"
   +            },
   +            "enum": {
   +              "type": "array",
   +              "items": {
   +                "type": "string"
   +              },
   +              "minItems": 1
   +            },
   +            "observable": {
   +              "type": "boolean"
   +            },
   +            "readable": {
   +              "type": "boolean"
   +            },
   +            "writable": {
   +              "type": "boolean"
   +            },
   +            "description": {
   +              "type": "string"
   +            },
   +            "label": {
   +              "type": "string"
   +            },
   +            "$comment": {
   +              "type": "string"
   +            },
   +            "sdfRef": {
   +              "$ref": "#/definitions/sdf-pointer"
   +            },
   +            "sdfRequired": {
   +              "$ref": "#/definitions/pointer-list"
   +            },
   +            "const": {
   +              "$ref": "#/definitions/allowed-types"

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   +            },
   +            "default": {
   +              "$ref": "#/definitions/allowed-types"
   +            },
   +            "minimum": {
   +              "type": "number"
   +            },
   +            "maximum": {
   +              "type": "number"
   +            },
   +            "exclusiveMinimum": {
   +              "type": "number"
   +            },
   +            "exclusiveMaximum": {
   +              "type": "number"
   +            },
   +            "multipleOf": {
   +              "type": "number"
   +            },
   +            "minLength": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "maxLength": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "pattern": {
   +              "type": "string"
   +            },
   +            "format": {
   +              "$ref": "#/definitions/format-"
   +            },
   +            "minItems": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "maxItems": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "uniqueItems": {
   +              "type": "boolean"
   +            },
   +            "items": {
   +              "$ref": "#/definitions/jso-items"
   +            },
   +            "unit": {
   +              "type": "string"
   +            },
   +            "nullable": {
   +              "type": "boolean"

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   +            },
   +            "sdfType": {
   +              "$ref": "#/definitions/sdfType-"
   +            },
   +            "contentFormat": {
   +              "type": "string"
   +            }
   +          },
   +          "additionalProperties": false
   +        },
   +        {
   +          "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },
   +          "properties": {
   +            "type": {
   +              "type": "string",
   +              "const": "object"
   +            },
   +            "required": {
   +              "type": "array",
   +              "items": {
   +                "type": "string"
   +              },
   +              "minItems": 1
   +            },
   +            "properties": {
   +              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
   +            },
   +            "enum": {
   +              "type": "array",
   +              "items": {
   +                "type": "string"
   +              },
   +              "minItems": 1
   +            },
   +            "observable": {
   +              "type": "boolean"
   +            },
   +            "readable": {
   +              "type": "boolean"
   +            },
   +            "writable": {
   +              "type": "boolean"
   +            },
   +            "description": {

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   +              "type": "string"
   +            },
   +            "label": {
   +              "type": "string"
   +            },
   +            "$comment": {
   +              "type": "string"
   +            },
   +            "sdfRef": {
   +              "$ref": "#/definitions/sdf-pointer"
   +            },
   +            "sdfRequired": {
   +              "$ref": "#/definitions/pointer-list"
   +            },
   +            "const": {
   +              "$ref": "#/definitions/allowed-types"
   +            },
   +            "default": {
   +              "$ref": "#/definitions/allowed-types"
   +            },
   +            "minimum": {
   +              "type": "number"
   +            },
   +            "maximum": {
   +              "type": "number"
   +            },
   +            "exclusiveMinimum": {
   +              "type": "number"
   +            },
   +            "exclusiveMaximum": {
   +              "type": "number"
   +            },
   +            "multipleOf": {
   +              "type": "number"
   +            },
   +            "minLength": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "maxLength": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "pattern": {
   +              "type": "string"
   +            },
   +            "format": {
   +              "$ref": "#/definitions/format-"
   +            },
   +            "minItems": {

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   +              "$ref": "#/definitions/uint"
   +            },
   +            "maxItems": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "uniqueItems": {
   +              "type": "boolean"
   +            },
   +            "items": {
   +              "$ref": "#/definitions/jso-items"
   +            },
   +            "unit": {
   +              "type": "string"
   +            },
   +            "nullable": {
   +              "type": "boolean"
   +            },
   +            "sdfType": {
   +              "$ref": "#/definitions/sdfType-"
   +            },
   +            "contentFormat": {
   +              "type": "string"
   +            }
   +          },
   +          "additionalProperties": false
   +        },
   +        {
   +          "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },
              "properties": {
                "type": {
   -              "type": "string",
   -              "const": "object"
   +              "type": "string"
                },
   -            "required": {
   +            "enum": {
                  "type": "array",
                  "items": {
                    "type": "string"
                  },
                  "minItems": 1
                },
   -            "properties": {
   -              "$ref": "#/definitions/sdfData-sdfChoice-properties-"

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   -            },
   -            "sdfChoice": {
   -              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
   -            },
                "observable": {
                  "type": "boolean"
                },
                "readable": {
                  "type": "boolean"
                },
                "writable": {
                  "type": "boolean"
                },
                "description": {
                  "type": "string"
                },
                "label": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "sdfRequired": {
                  "$ref": "#/definitions/pointer-list"
                },
                "const": {
                  "$ref": "#/definitions/allowed-types"
                },
                "default": {
                  "$ref": "#/definitions/allowed-types"
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "exclusiveMinimum": {
                  "type": "number"
                },
                "exclusiveMaximum": {
                  "type": "number"
                },
                "multipleOf": {
                  "type": "number"

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                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                },
                "pattern": {
                  "type": "string"
                },
                "format": {
                  "$ref": "#/definitions/format-"
                },
                "minItems": {
                  "$ref": "#/definitions/uint"
                },
                "maxItems": {
                  "$ref": "#/definitions/uint"
                },
                "uniqueItems": {
                  "type": "boolean"
                },
                "items": {
                  "$ref": "#/definitions/jso-items"
                },
                "unit": {
                  "type": "string"
                },
                "nullable": {
                  "type": "boolean"
                },
                "sdfType": {
                  "$ref": "#/definitions/sdfType-"
                },
                "contentFormat": {
                  "type": "string"
                }
              },
              "additionalProperties": false
   -        },
   +        }
   +      ]
   +    },
   +    "dataqualities": {
   +      "anyOf": [
            {
              "type": "object",
   +          "patternProperties": {

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   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },
              "properties": {
                "type": {
                  "$ref": "#/definitions/type-"
                },
   -            "enum": {
   -              "type": "array",
   -              "items": {
   -                "type": "string"
   -              },
   -              "minItems": 1
   -            },
   -            "observable": {
   -              "type": "boolean"
   -            },
   -            "readable": {
   -              "type": "boolean"
   -            },
   -            "writable": {
   -              "type": "boolean"
   +            "sdfChoice": {
   +              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
                },
                "description": {
                  "type": "string"
                },
                "label": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "sdfRequired": {
                  "$ref": "#/definitions/pointer-list"
                },
                "const": {
                  "$ref": "#/definitions/allowed-types"
                },
                "default": {
                  "$ref": "#/definitions/allowed-types"
                },
                "minimum": {
                  "type": "number"

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                },
                "maximum": {
                  "type": "number"
                },
                "exclusiveMinimum": {
                  "type": "number"
                },
                "exclusiveMaximum": {
                  "type": "number"
                },
                "multipleOf": {
                  "type": "number"
                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                },
                "pattern": {
                  "type": "string"
                },
                "format": {
                  "$ref": "#/definitions/format-"
                },
                "minItems": {
                  "$ref": "#/definitions/uint"
                },
                "maxItems": {
                  "$ref": "#/definitions/uint"
                },
                "uniqueItems": {
                  "type": "boolean"
                },
                "items": {
                  "$ref": "#/definitions/jso-items"
                },
                "unit": {
                  "type": "string"
                },
                "nullable": {
                  "type": "boolean"
                },
                "sdfType": {
                  "$ref": "#/definitions/sdfType-"
                },
                "contentFormat": {
                  "type": "string"

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                }
              },
              "additionalProperties": false
            },
            {
              "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },
              "properties": {
                "type": {
                  "type": "string",
                  "const": "object"
                },
                "required": {
                  "type": "array",
                  "items": {
                    "type": "string"
                  },
                  "minItems": 1
                },
                "properties": {
                  "$ref": "#/definitions/sdfData-sdfChoice-properties-"
                },
   -            "enum": {
   -              "type": "array",
   -              "items": {
   -                "type": "string"
   -              },
   -              "minItems": 1
   -            },
   -            "observable": {
   -              "type": "boolean"
   -            },
   -            "readable": {
   -              "type": "boolean"
   -            },
   -            "writable": {
   -              "type": "boolean"
   +            "sdfChoice": {
   +              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
                },
                "description": {
                  "type": "string"
                },
                "label": {
                  "type": "string"

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                },
                "$comment": {
                  "type": "string"
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "sdfRequired": {
                  "$ref": "#/definitions/pointer-list"
                },
                "const": {
                  "$ref": "#/definitions/allowed-types"
                },
                "default": {
                  "$ref": "#/definitions/allowed-types"
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "exclusiveMinimum": {
                  "type": "number"
                },
                "exclusiveMaximum": {
                  "type": "number"
                },
                "multipleOf": {
                  "type": "number"
                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                },
                "pattern": {
                  "type": "string"
                },
                "format": {
                  "$ref": "#/definitions/format-"
                },
                "minItems": {
                  "$ref": "#/definitions/uint"
                },
                "maxItems": {
                  "$ref": "#/definitions/uint"

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                },
                "uniqueItems": {
                  "type": "boolean"
                },
                "items": {
                  "$ref": "#/definitions/jso-items"
                },
                "unit": {
                  "type": "string"
                },
                "nullable": {
                  "type": "boolean"
                },
                "sdfType": {
                  "$ref": "#/definitions/sdfType-"
                },
                "contentFormat": {
                  "type": "string"
                }
              },
              "additionalProperties": false
   -        }
   -      ]
   -    },
   -    "dataqualities": {
   -      "anyOf": [
   +        },
            {
              "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },
              "properties": {
                "type": {
   -              "$ref": "#/definitions/type-"
   +              "type": "string"
                },
                "sdfChoice": {
                  "$ref": "#/definitions/sdfData-sdfChoice-properties-"
                },
                "description": {
                  "type": "string"
                },
                "label": {
                  "type": "string"
                },
                "$comment": {

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                  "type": "string"
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "sdfRequired": {
                  "$ref": "#/definitions/pointer-list"
                },
                "const": {
                  "$ref": "#/definitions/allowed-types"
                },
                "default": {
                  "$ref": "#/definitions/allowed-types"
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "exclusiveMinimum": {
                  "type": "number"
                },
                "exclusiveMaximum": {
                  "type": "number"
                },
                "multipleOf": {
                  "type": "number"
                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                },
                "pattern": {
                  "type": "string"
                },
                "format": {
                  "$ref": "#/definitions/format-"
                },
                "minItems": {
                  "$ref": "#/definitions/uint"
                },
                "maxItems": {
                  "$ref": "#/definitions/uint"
                },
                "uniqueItems": {

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                  "type": "boolean"
                },
                "items": {
                  "$ref": "#/definitions/jso-items"
                },
                "unit": {
                  "type": "string"
                },
                "nullable": {
                  "type": "boolean"
                },
                "sdfType": {
                  "$ref": "#/definitions/sdfType-"
                },
                "contentFormat": {
                  "type": "string"
                }
              },
              "additionalProperties": false
            },
            {
              "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },
              "properties": {
                "type": {
   -              "type": "string",
   -              "const": "object"
   +              "$ref": "#/definitions/type-"
                },
   -            "required": {
   +            "enum": {
                  "type": "array",
                  "items": {
                    "type": "string"
                  },
                  "minItems": 1
                },
   -            "properties": {
   -              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
   -            },
   -            "sdfChoice": {
   -              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
   -            },
                "description": {
                  "type": "string"

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                },
                "label": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "sdfRequired": {
                  "$ref": "#/definitions/pointer-list"
                },
                "const": {
                  "$ref": "#/definitions/allowed-types"
                },
                "default": {
                  "$ref": "#/definitions/allowed-types"
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "exclusiveMinimum": {
                  "type": "number"
                },
                "exclusiveMaximum": {
                  "type": "number"
                },
                "multipleOf": {
                  "type": "number"
                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                },
                "pattern": {
                  "type": "string"
                },
                "format": {
                  "$ref": "#/definitions/format-"
                },
                "minItems": {
                  "$ref": "#/definitions/uint"

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                },
                "maxItems": {
                  "$ref": "#/definitions/uint"
                },
                "uniqueItems": {
                  "type": "boolean"
                },
                "items": {
                  "$ref": "#/definitions/jso-items"
                },
                "unit": {
                  "type": "string"
                },
                "nullable": {
                  "type": "boolean"
                },
                "sdfType": {
                  "$ref": "#/definitions/sdfType-"
                },
                "contentFormat": {
                  "type": "string"
                }
              },
              "additionalProperties": false
            },
            {
              "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },
              "properties": {
                "type": {
   -              "$ref": "#/definitions/type-"
   +              "type": "string",
   +              "const": "object"
   +            },
   +            "required": {
   +              "type": "array",
   +              "items": {
   +                "type": "string"
   +              },
   +              "minItems": 1
   +            },
   +            "properties": {
   +              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
                },
                "enum": {

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                  "type": "array",
                  "items": {
                    "type": "string"
                  },
                  "minItems": 1
                },
                "description": {
                  "type": "string"
                },
                "label": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "sdfRequired": {
                  "$ref": "#/definitions/pointer-list"
                },
                "const": {
                  "$ref": "#/definitions/allowed-types"
                },
                "default": {
                  "$ref": "#/definitions/allowed-types"
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "exclusiveMinimum": {
                  "type": "number"
                },
                "exclusiveMaximum": {
                  "type": "number"
                },
                "multipleOf": {
                  "type": "number"
                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                },

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                "pattern": {
                  "type": "string"
                },
                "format": {
                  "$ref": "#/definitions/format-"
                },
                "minItems": {
                  "$ref": "#/definitions/uint"
                },
                "maxItems": {
                  "$ref": "#/definitions/uint"
                },
                "uniqueItems": {
                  "type": "boolean"
                },
                "items": {
                  "$ref": "#/definitions/jso-items"
                },
                "unit": {
                  "type": "string"
                },
                "nullable": {
                  "type": "boolean"
                },
                "sdfType": {
                  "$ref": "#/definitions/sdfType-"
                },
                "contentFormat": {
                  "type": "string"
                }
              },
              "additionalProperties": false
            },
            {
              "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },
              "properties": {
                "type": {
   -              "type": "string",
   -              "const": "object"
   -            },
   -            "required": {
   -              "type": "array",
   -              "items": {
   -                "type": "string"

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   -              },
   -              "minItems": 1
   -            },
   -            "properties": {
   -              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
   +              "type": "string"
                },
                "enum": {
                  "type": "array",
                  "items": {
                    "type": "string"
                  },
                  "minItems": 1
                },
                "description": {
                  "type": "string"
                },
                "label": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "sdfRequired": {
                  "$ref": "#/definitions/pointer-list"
                },
                "const": {
                  "$ref": "#/definitions/allowed-types"
                },
                "default": {
                  "$ref": "#/definitions/allowed-types"
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "exclusiveMinimum": {
                  "type": "number"
                },
                "exclusiveMaximum": {
                  "type": "number"
                },
                "multipleOf": {

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                  "type": "number"
                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                },
                "pattern": {
                  "type": "string"
                },
                "format": {
                  "$ref": "#/definitions/format-"
                },
                "minItems": {
                  "$ref": "#/definitions/uint"
                },
                "maxItems": {
                  "$ref": "#/definitions/uint"
                },
                "uniqueItems": {
                  "type": "boolean"
                },
                "items": {
                  "$ref": "#/definitions/jso-items"
                },
                "unit": {
                  "type": "string"
                },
                "nullable": {
                  "type": "boolean"
                },
                "sdfType": {
                  "$ref": "#/definitions/sdfType-"
                },
                "contentFormat": {
                  "type": "string"
                }
              },
              "additionalProperties": false
            }
          ]
        },
        "allowed-types": {
          "anyOf": [
            {
              "type": "number"
            },

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            {
              "type": "string"
            },
            {
              "type": "boolean"
            },
            {
              "type": "null"
            },
            {
              "type": "array",
              "items": {
                "type": "number"
              }
            },
            {
              "type": "array",
              "items": {
                "type": "string"
              }
            },
            {
              "type": "array",
              "items": {
                "type": "boolean"
              }
            },
            {
              "type": "object",
              "additionalProperties": {
              }
   +        },
   +        {
            }
          ]
        },
        "uint": {
          "type": "integer",
          "minimum": 0
        },
        "jso-items": {
          "anyOf": [
            {
              "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },

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              "properties": {
                "type": {
                  "type": "string",
                  "enum": [
                    "number",
                    "string",
                    "boolean",
                    "integer"
                  ]
                },
                "sdfChoice": {
                  "$ref": "#/definitions/sdfData-sdfChoice-properties-"
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "description": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "format": {
                  "type": "string"
                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                }
              },
              "additionalProperties": false
            },
            {
              "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },
              "properties": {
                "type": {

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                  "type": "string",
                  "const": "object"
                },
                "required": {
                  "type": "array",
                  "items": {
                    "type": "string"
                  },
                  "minItems": 1
                },
                "properties": {
                  "$ref": "#/definitions/sdfData-sdfChoice-properties-"
                },
                "sdfChoice": {
                  "$ref": "#/definitions/sdfData-sdfChoice-properties-"
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "description": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "format": {
                  "type": "string"
                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                }
              },
              "additionalProperties": false
            },
            {
              "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }

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   +          },
   +          "properties": {
   +            "type": {
   +              "type": "string"
   +            },
   +            "sdfChoice": {
   +              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
   +            },
   +            "sdfRef": {
   +              "$ref": "#/definitions/sdf-pointer"
   +            },
   +            "description": {
   +              "type": "string"
   +            },
   +            "$comment": {
   +              "type": "string"
   +            },
   +            "minimum": {
   +              "type": "number"
   +            },
   +            "maximum": {
   +              "type": "number"
   +            },
   +            "format": {
   +              "type": "string"
   +            },
   +            "minLength": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "maxLength": {
   +              "$ref": "#/definitions/uint"
   +            }
   +          },
   +          "additionalProperties": false
   +        },
   +        {
   +          "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },
              "properties": {
                "type": {
                  "type": "string",
                  "enum": [
                    "number",
                    "string",
                    "boolean",

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                    "integer"
                  ]
                },
                "enum": {
                  "type": "array",
                  "items": {
                    "type": "string"
                  },
                  "minItems": 1
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "description": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "format": {
                  "type": "string"
                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                }
              },
              "additionalProperties": false
            },
            {
              "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +            }
   +          },
              "properties": {
                "type": {
                  "type": "string",
                  "const": "object"
                },

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                "required": {
                  "type": "array",
                  "items": {
                    "type": "string"
                  },
                  "minItems": 1
                },
                "properties": {
                  "$ref": "#/definitions/sdfData-sdfChoice-properties-"
                },
                "enum": {
                  "type": "array",
                  "items": {
                    "type": "string"
                  },
                  "minItems": 1
                },
                "sdfRef": {
                  "$ref": "#/definitions/sdf-pointer"
                },
                "description": {
                  "type": "string"
                },
                "$comment": {
                  "type": "string"
                },
                "minimum": {
                  "type": "number"
                },
                "maximum": {
                  "type": "number"
                },
                "format": {
                  "type": "string"
                },
                "minLength": {
                  "$ref": "#/definitions/uint"
                },
                "maxLength": {
                  "$ref": "#/definitions/uint"
                }
              },
              "additionalProperties": false
   +        },
   +        {
   +          "type": "object",
   +          "patternProperties": {
   +            "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {

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   +            }
   +          },
   +          "properties": {
   +            "type": {
   +              "type": "string"
   +            },
   +            "enum": {
   +              "type": "array",
   +              "items": {
   +                "type": "string"
   +              },
   +              "minItems": 1
   +            },
   +            "sdfRef": {
   +              "$ref": "#/definitions/sdf-pointer"
   +            },
   +            "description": {
   +              "type": "string"
   +            },
   +            "$comment": {
   +              "type": "string"
   +            },
   +            "minimum": {
   +              "type": "number"
   +            },
   +            "maximum": {
   +              "type": "number"
   +            },
   +            "format": {
   +              "type": "string"
   +            },
   +            "minLength": {
   +              "$ref": "#/definitions/uint"
   +            },
   +            "maxLength": {
   +              "$ref": "#/definitions/uint"
   +            }
   +          },
   +          "additionalProperties": false
            }
          ]
        },
   +    "sdftype-name": {
   +      "type": "string",
   +      "pattern": "^[a-z][\\-a-z0-9]*$"
   +    },
        "actionqualities": {
          "type": "object",

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          "properties": {
            "description": {
              "type": "string"
            },
            "label": {
              "type": "string"
            },
            "$comment": {
              "type": "string"
            },
            "sdfRef": {
              "$ref": "#/definitions/sdf-pointer"
            },
            "sdfRequired": {
              "$ref": "#/definitions/pointer-list"
            },
            "sdfInputData": {
              "$ref": "#/definitions/parameter-list"
            },
            "sdfOutputData": {
              "$ref": "#/definitions/parameter-list"
            },
            "sdfData": {
              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
            }
          },
   +      "patternProperties": {
   +        "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +        }
   +      },
          "additionalProperties": false
        },
        "parameter-list": {
          "$ref": "#/definitions/dataqualities"
        },
        "eventqualities": {
          "type": "object",
          "properties": {
            "description": {
              "type": "string"
            },
            "label": {
              "type": "string"
            },
            "$comment": {
              "type": "string"
            },
            "sdfRef": {

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              "$ref": "#/definitions/sdf-pointer"
            },
            "sdfRequired": {
              "$ref": "#/definitions/pointer-list"
            },
            "sdfOutputData": {
              "$ref": "#/definitions/parameter-list"
            },
            "sdfData": {
              "$ref": "#/definitions/sdfData-sdfChoice-properties-"
            }
          },
   +      "patternProperties": {
   +        "^(?:[a-z][a-z0-9]*:)?[a-z$][A-Za-z$0-9]*$": {
   +        }
   +      },
          "additionalProperties": false
        },
        "format-": {
   -      "type": "string",
   -      "enum": [
   -        "date-time",
   -        "date",
   -        "time",
   -        "uri",
   -        "uri-reference",
   -        "uuid"
   +      "anyOf": [
   +        {
   +          "type": "string",
   +          "const": "date-time"
   +        },
   +        {
   +          "type": "string",
   +          "const": "date"
   +        },
   +        {
   +          "type": "string",
   +          "const": "time"
   +        },
   +        {
   +          "type": "string",
   +          "const": "uri"
   +        },
   +        {
   +          "type": "string",
   +          "const": "uri-reference"
   +        },

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   +        {
   +          "type": "string",
   +          "const": "uuid"
   +        },
   +        {
   +          "type": "string"
   +        }
   +      ]
   +    },
   +    "sdfType-": {
   +      "anyOf": [
   +        {
   +          "type": "string",
   +          "const": "byte-string"
   +        },
   +        {
   +          "type": "string",
   +          "const": "unix-time"
   +        },
   +        {
   +          "$ref": "#/definitions/sdftype-name"
   +        }
          ]
        },
        "sdfData-sdfChoice-properties-": {
          "type": "object",
          "additionalProperties": {
            "$ref": "#/definitions/dataqualities"
          }
        },
        "type-": {
          "type": "string",
          "enum": [
            "number",
            "string",
            "boolean",
            "integer",
            "array"
          ]
        },
   -    "sdfAction-": {
   +    "sdfEvent-": {
          "type": "object",
          "additionalProperties": {
   -        "$ref": "#/definitions/actionqualities"
   +        "$ref": "#/definitions/eventqualities"
          }
        },

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   -    "sdfProperty-": {
   +    "sdfAction-": {
          "type": "object",
          "additionalProperties": {
   -        "$ref": "#/definitions/propertyqualities"
   +        "$ref": "#/definitions/actionqualities"
          }
        },
   -    "sdfEvent-": {
   +    "sdfProperty-": {
          "type": "object",
          "additionalProperties": {
   -        "$ref": "#/definitions/eventqualities"
   +        "$ref": "#/definitions/propertyqualities"
          }
   -    },
   -    "sdfType-": {
   -      "type": "string",
   -      "enum": [
   -        "byte-string",
   -        "unix-time"
   -      ]
        }
      }
    }

Appendix C.  Data Qualities inspired by json-schema.org

   Data qualities define data used in SDF affordances at an information
   model level.  A popular way to describe JSON data at a data model
   level is proposed by a number of drafts on json-schema.org (which
   collectively are abbreviated JSO here); for reference to a popular
   version we will point here to [JSO7] and [JSO7V].  As the vocabulary
   used by JSO is familiar to many JSON modelers, the present
   specification borrows some of the terms and ports their semantics to
   the information model level needed for SDF.

   The main data quality imported is the "type".  In SDF, this can take
   one of six (text string) values, which are discussed in the following
   subsections (note that the JSO type "null" is not supported as a
   value of this data quality in SDF).

   The additional quality "const" restricts the data to one specific
   value (given as the value of the const quality).

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   Similarly, the additional quality "default" provides data that can be
   used in the absence of the data (given as the value of the const
   quality); this is mainly documentary and not very well-defined for
   SDF as no process is defined that would add default values to an
   instance of some interaction data.

C.1.  type "number", type "integer"

   The types "number" and "integer" are associated with floating point
   and integer numbers, as they are available in JSON.  A type value of
   integer means that only integer values of JSON numbers can be used
   (note that 10.0 is an integer value, even if it is in a notation that
   would also allow non-zero decimal fractions).

   The additional data qualities "minimum", "maximum",
   "exclusiveMinimum", "exclusiveMaximum" provide number values that
   serve as inclusive/exclusive lower/upper bounds for the number.
   (Note that the Boolean form of "exclusiveMinimum"/"exclusiveMaximum"
   found in earlier JSO drafts [JSO4V] is not used.)

   The data quality "multipleOf" gives a positive number that constrains
   the data value to be an integer multiple of the number given.  (Type
   "integer" can also be expressed as a "multipleOf" quality of value 1,
   unless another "multipleOf" quality is present.)

C.2.  type "string"

   The type "string" is associated with Unicode text string values as
   they can be represented in JSON.

   The length (as measured in characters) can be constrained by the
   additional data qualities "minLength" and "maxLength", which are
   inclusive bounds.

   (More specifically, Unicode text strings as defined in this
   specification are sequences of Unicode scalar values, the number of
   which is taken as the length of such a text string.  Note that
   earlier drafts of this specification explained text string length
   values in bytes, which however is not meaningful unless bound to a
   specific encoding — which could be UTF-8, if this unusual behavior is
   to be provided in an extension.)

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   The data quality "pattern" takes a string value that is interpreted
   as an [ECMA-262] regular expression in Unicode mode that constrains
   the string (note that these are not anchored by default, so unless ^
   and $ anchors are employed, ECMA-262 regular expressions match any
   string that _contains_ a match).  The JSO proposals acknowledge that
   regular expression support is rather diverse in various platforms, so
   the suggestion is to limit them to:

   *  characters;
   *  character classes in square brackets, including ranges; their
      complements;
   *  simple quantifiers *, +, ?, and range quantifiers {n}, {n,m}, and
      {n,};
   *  grouping parentheses;
   *  the choice operator |;
   *  and anchors (beginning-of-input ^ and end-of-input $).

   Note that this subset is somewhat similar to the subset introduced by
   I-Regexps [RFC9485], which however are anchored regular expressions,
   and which include certain backslash escapes for characters and
   character classes.

   The additional data quality "format" can take one of the following
   values.  Note that, at an information model level, the presence of
   this data quality changes the type from being a simple text string to
   the abstract meaning of the format given (i.e., the format "date-
   time" is less about the specific syntax employed in [RFC3339] than
   about the usage as an absolute point in civil time).

   *  "date-time", "date", "time": An [RFC3339] date-time, full-date, or
      full-time, respectively.
   *  "uri", "uri-reference": An [RFC3986] URI or URI Reference,
      respectively.
   *  "uuid": An [RFC4122] UUID.

C.3.  type "boolean"

   The type "boolean" can take the values "true" or "false".

C.4.  type "array"

   The type "array" is associated with arrays as they are available in
   JSON.

   The additional quality "items" gives the type that each of the
   elements of the array must match.

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   The number of elements in the array can be constrained by the
   additional data qualities "minItems" and "maxItems", which are
   inclusive bounds.

   The additional data quality "uniqueItems" gives a Boolean value that,
   if true, requires the elements to be all different.

C.5.  type "object"

   The type "object" is associated with maps, from strings to values, as
   they are available in JSON.

   The additional quality "properties" is a map the entries of which
   describe entries in the specified JSON map: The key gives an
   allowable map key for the specified JSON map, and the value is a map
   with a named set of data qualities giving the type for the
   corresponding value in the specified JSON map.

   All entries specified this way are optional, unless they are listed
   in the value of the additional quality "required", which is an array
   of string values that give the key names of required entries.

   Note that the term "properties" as an additional quality for defining
   map entries is unrelated to sdfProperty.

C.6.  Implementation notes

   JSO-based keywords are also used in the specification techniques of a
   number of ecosystems, but some adjustments may be required.

   For instance, [OCF] is based on Swagger 2.0 which appears to be based
   on "draft-4" [JSO4][JSO4V] (also called draft-5, but semantically
   intended to be equivalent to draft-4).  The "exclusiveMinimum" and
   "exclusiveMaximum" keywords use the Boolean form there, so on import
   to SDF their values have to be replaced by the values of the
   respective "minimum"/"maximum" keyword, which are themselves then
   removed; the reverse transformation applies on export.

Appendix D.  Composition Examples

   This appendix contains two examples illustrating different
   composition approaches using the sdfThing quality.

D.1.  Outlet Strip Example

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   {
     "sdfThing": {
       "outlet-strip": {
         "label": "Outlet strip",
         "description": "Contains a number of Sockets",
         "sdfObject": {
           "socket": {
             "description": "An array of sockets in the outlet strip",
             "minItems": 2,
             "maxItems": 10
           }
         }
       }
     }
   }

                                  Figure 6

D.2.  Refrigerator-Freezer Example

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   {
     "sdfThing": {
       "refrigerator-freezer": {
         "description": "A refrigerator combined with a freezer",
         "sdfProperty": {
           "status": {
             "type": "boolean",
             "description":
   "Indicates if the refrigerator-freezer is powered"
           }
         },
         "sdfObject": {
           "refrigerator": {
             "description": "A refrigerator compartment",
             "sdfProperty": {
               "temperature": {
                 "sdfRef": "#/sdfProproperty/temperature",
                 "maximum": 8
               }
             }
           },
           "freezer": {
             "label": "A freezer compartment",
             "sdfProperty": {
               "temperature": {
                 "sdfRef": "#/sdfProproperty/temperature",
                 "maximum": -6
               }
             }
           }
         }
       }
     },
     "sdfProperty": {
       "temperature": {
         "description": "The temperature for this compartment",
         "type": "number",
         "unit": "Cel"
       }
     }
   }

                                  Figure 7

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Acknowledgements

   This specification is based on sdf.md and sdf-schema.json in the old
   one-data-model language repository, as well as Ari Keränen's "alt-
   schema" from the Ericsson Research ipso-odm repository (which is now
   under subdirectory sdflint in the one-data model tools repository).

Contributors

   Jan Romann
   Universität Bremen
   Email: jan.romann@uni-bremen.de

   Wouter van der Beek
   Cascoda Ltd.
   Threefield House
   Threefield Lane
   Southampton
   United Kingdom
   Email: w.vanderbeek@cascoda.com

Authors' Addresses

   Michael Koster (editor)
   KTC
   29415 Alderpoint Road
   Blocksburg, CA,  95514
   United States of America
   Phone: +1-707-502-5136
   Email: michaeljohnkoster@gmail.com

   Carsten Bormann (editor)
   Universität Bremen TZI
   Postfach 330440
   D-28359 Bremen
   Germany
   Phone: +49-421-218-63921
   Email: cabo@tzi.org

   Ari Keränen
   Ericsson
   FI-02420 Jorvas
   Finland
   Email: ari.keranen@ericsson.com

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