Semantic Definition Format (SDF) for Data and Interactions of Things
draft-ietf-asdf-sdf-11
| Document | Type | Active Internet-Draft (asdf WG) | |
|---|---|---|---|
| Authors | Michael Koster , Carsten Bormann | ||
| Last updated | 2022-03-10 (Latest revision 2022-02-28) | ||
| Replaces | draft-onedm-t2trg-sdf | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | plain text html xml htmlized pdfized bibtex | ||
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| Document shepherd | Michael Richardson | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Yes | ||
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| Send notices to | mcr+ietf@sandelman.ca |
draft-ietf-asdf-sdf-11
ASDF M. Koster, Ed.
Internet-Draft PassiveLogic
Intended status: Standards Track C. Bormann, Ed.
Expires: 1 September 2022 Universität Bremen TZI
28 February 2022
Semantic Definition Format (SDF) for Data and Interactions of Things
draft-ietf-asdf-sdf-11
Abstract
The Semantic Definition Format (SDF) is a format for domain experts
to use in the creation and maintenance of data and interaction models
in the Internet of Things. It was created as a common language for
use in the development of the One Data Model liaison organization
(OneDM) definitions. Tools convert this format to database formats
and other serializations as needed.
An SDF specification describes definitions of SDF Objects and their
associated interactions (Events, Actions, Properties), as well as the
Data types for the information exchanged in those interactions.
// A JSON format representation of SDF 1.0 was defined in version
// (-00) of this document; version (-05) was designated as an
// _implementation draft_, labeled SDF 1.1, at the IETF110 meeting of
// the ASDF WG (2021-03-11). The present version (-11) collects a
// few smaller changes as input to the 2022-02-28 ASDF WG interim.
// It also removes deprecated elements from SDF 1.0.
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/.
Source for this draft and an issue tracker can be found at
https://github.com/ietf-wg-asdf/SDF.
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Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 1 September 2022.
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology and Conventions . . . . . . . . . . . . . . . 4
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Example Definition . . . . . . . . . . . . . . . . . . . 6
2.2. Elements of an SDF model . . . . . . . . . . . . . . . . 8
2.2.1. sdfObject . . . . . . . . . . . . . . . . . . . . . . 9
2.2.2. sdfProperty . . . . . . . . . . . . . . . . . . . . . 10
2.2.3. sdfAction . . . . . . . . . . . . . . . . . . . . . . 11
2.2.4. sdfEvent . . . . . . . . . . . . . . . . . . . . . . 11
2.2.5. sdfData . . . . . . . . . . . . . . . . . . . . . . . 12
2.2.6. sdfThing . . . . . . . . . . . . . . . . . . . . . . 12
3. SDF structure . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1. Information block . . . . . . . . . . . . . . . . . . . . 13
3.2. Namespaces block . . . . . . . . . . . . . . . . . . . . 14
3.3. Definitions block . . . . . . . . . . . . . . . . . . . . 15
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4. Names and namespaces . . . . . . . . . . . . . . . . . . . . 16
4.1. Structure . . . . . . . . . . . . . . . . . . . . . . . . 16
4.2. Contributing global names . . . . . . . . . . . . . . . . 16
4.3. Referencing global names . . . . . . . . . . . . . . . . 17
4.4. sdfRef . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.5. sdfRequired . . . . . . . . . . . . . . . . . . . . . . . 19
4.6. Common Qualities . . . . . . . . . . . . . . . . . . . . 20
4.7. Data Qualities . . . . . . . . . . . . . . . . . . . . . 21
4.7.1. sdfType . . . . . . . . . . . . . . . . . . . . . . . 23
4.7.2. sdfChoice . . . . . . . . . . . . . . . . . . . . . . 24
5. Keywords for definition groups . . . . . . . . . . . . . . . 26
5.1. sdfObject . . . . . . . . . . . . . . . . . . . . . . . . 26
5.2. sdfProperty . . . . . . . . . . . . . . . . . . . . . . . 27
5.3. sdfAction . . . . . . . . . . . . . . . . . . . . . . . . 28
5.4. sdfEvent . . . . . . . . . . . . . . . . . . . . . . . . 29
5.5. sdfData . . . . . . . . . . . . . . . . . . . . . . . . . 29
6. High Level Composition . . . . . . . . . . . . . . . . . . . 30
6.1. Paths in the model namespaces . . . . . . . . . . . . . . 30
6.2. Modular Composition . . . . . . . . . . . . . . . . . . . 31
6.2.1. Use of the "sdfRef" keyword to re-use a definition . 31
6.3. sdfThing . . . . . . . . . . . . . . . . . . . . . . . . 32
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
7.1. Media Type . . . . . . . . . . . . . . . . . . . . . . . 32
7.2. IETF URN Sub-namespace for Unit Names
(urn:ietf:params:unit) . . . . . . . . . . . . . . . . . 33
7.3. Registries . . . . . . . . . . . . . . . . . . . . . . . 33
8. Security Considerations . . . . . . . . . . . . . . . . . . . 33
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 34
9.1. Normative References . . . . . . . . . . . . . . . . . . 34
9.2. Informative References . . . . . . . . . . . . . . . . . 35
Appendix A. Formal Syntax of SDF . . . . . . . . . . . . . . . . 37
Appendix B. json-schema.org Rendition of SDF Syntax . . . . . . 41
Appendix C. Data Qualities inspired by json-schema.org . . . . . 79
C.1. type "number", type "integer" . . . . . . . . . . . . . . 80
C.2. type "string" . . . . . . . . . . . . . . . . . . . . . . 80
C.3. type "boolean" . . . . . . . . . . . . . . . . . . . . . 81
C.4. type "array" . . . . . . . . . . . . . . . . . . . . . . 81
C.5. type "object" . . . . . . . . . . . . . . . . . . . . . . 81
C.6. Implementation notes . . . . . . . . . . . . . . . . . . 82
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 82
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 83
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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
in the Internet of Things. It was created as a common language for
use in the development of the One Data Model liaison organization
(OneDM) definitions. Tools convert this format to database formats
and other serializations as needed.
An SDF specification describes definitions of SDF Objects and their
associated interactions (Events, Actions, Properties), as well as the
Data types for the information exchanged in those interactions.
// A JSON format representation of SDF 1.0 was defined in version
// (-00) of this document; version (-05) was designated as an
// _implementation draft_, labeled SDF 1.1, at the IETF110 meeting of
// the ASDF WG (2021-03-11). The present version (-11) collects a
// few smaller changes as input to the 2022-02-28 ASDF WG interim.
// It also removes deprecated elements from SDF 1.0.
1.1. Terminology and Conventions
Thing: A physical item that is also made available in the Internet
of Things. The term is used here for Things that are notable for
their interaction with the physical world beyond interaction with
humans; a temperature sensor or a light might be a Thing, but a
router that employs both temperature sensors and indicator lights
might exhibit less Thingness, as the effects of its functioning
are mostly on the digital side.
Affordance: An element of an interface offered for interaction,
defining its possible uses or making clear how it can or should be
used. The term is used here for the digital interfaces of a Thing
only; it might also have physical affordances such as buttons,
dials, and displays.
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 (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.
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Group: An entry in the main SDF map and in certain nested
definitions that has a Class Name Keyword as its key and a map of
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 on an Object. (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 Object.
Event: An affordance that can potentially be used to obtain
information about what happened to an Object.
Object: A grouping of Property, Action, and Event definitions; the
main "atom" of reusable semantics for model construction. (Note
that JSON maps are often called JSON objects due to JSON's
JavaScript heritage; in this document, the term Object is
specifically reserved for the above grouping, even if the type
name "object" might be imported from a data definition language
with the other semantics.)
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.
Declaration: A reference to and a use of a definition within an
enclosing definition, intended to create component instances
within that enclosing definition. Every declaration can also be
used as a definition for reference in a different place.
Protocol Binding: A companion document to an SDF specification that
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defines how to map the abstract concepts in the specification into
the protocols in use in a specific ecosystem. Might supply URL
components, numeric IDs, and similar details.
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.
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 Object
called "Switch" (Figure 1).
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{
"info": {
"title": "Example file for OneDM 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 definition file
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.
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The sdfObject group lists the affordances of instances of this
object. The sdfProperty group lists the property affordances
described by the model; these represent various perspectives on the
state of the object. 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
Objects, the items listed in an sdfObject group, are the main "atom"
of reusable semantics for model construction. It 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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Optional qualities "minItems" and "maxItems" can be used to define
sdfObjects as arrays.
2.2.2. sdfProperty
sdfProperty is used to model elements of state within sdfObject
instances.
An instance of 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 a Property with
the given qualities to be potentially present in the containing
Object.
For definitions in sdfProperty and sdfData, SDF provides qualities
that can constrain the structure and values of data allowed in an
instance of these data, as well as qualities that associate semantics
to these data, for engineering units and unit scaling information.
For the data definition within sdfProperty or sdfData, SDF borrows
some vocabulary proposed for the drafts 4 and 7 of the json-
schema.org "JSON Schema" format (collectively called JSO here),
enhanced by qualities that are specific to SDF. Details about the
former are in Appendix C. For the current version of SDF, data are
constrained to be of simple types (number, string, Boolean), JSON
maps composed of named data ("objects"), and arrays of these types.
Syntax extension points are provided that can be used to provide
richer types in future versions 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.
Actions may have (or lack) qualities of idempotency and side-effect
safety.
The current version of 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 an
instance of an Object; these may result in a signal being stored or
emitted as a result.
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.
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The current version of 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 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.
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 groups enables definition of
models for complex devices that will use one or more sdfObject
definitions.
A definition in an sdfThing group can refine the metadata of the
definitions it is composed from: other definitions in sdfThing groups
definitions in sdfObject groups.
3. SDF structure
SDF definitions are contained in SDF files. One or more SDF files
can work together to provide the definitions and declarations that
are the payload of the SDF format.
A SDF definition file contains a single JSON map (JSON object). This
object has three blocks: the information block, the namespaces block,
and the definitions block.
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3.1. Information block
The information block contains generic meta data for the file 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 files will have policies that only SDF models
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.
+===========+========+==========+=================================+
| Quality | Type | Required | Description |
+===========+========+==========+=================================+
| title | string | no | A short summary to be displayed |
| | | | in search results, etc. |
+-----------+--------+----------+---------------------------------+
| version | string | no | The incremental version of the |
| | | | definition, format TBD |
+-----------+--------+----------+---------------------------------+
| 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 |
+-----------+--------+----------+---------------------------------+
Table 1: Qualities of the Information Block
While the format of the version string is marked as TBD, it is
intended 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).
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. (For models to be handled by the One Data Model
liaison group, this will typically be "BSD-3-Clause".)
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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 definition
file.
+==================+========+==========+=======================+
| 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 definition file does
not contribute to a global namespace. 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.
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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 (object), 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
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 current definition block.
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 Object definition is given in Figure 3:
"sdfObject": {
"foo": {
"sdfProperty": {
"bar": {
"type": "boolean"
}
}
}
}
Figure 3: Example Object definition
This example defines an Object "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.
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Some of the definitions are also declarations: the definition of the
entry "bar" in the property "foo" means that each instance of a "foo"
can have zero or one instance of a "bar". Entries within
sdfProperty, sdfAction, and sdfEvent, within sdfObject entries, are
declarations. Similarly, entries within an sdfThing describe
instances of sdfObject (or nested sdfThing) that form part of
instances of the Thing.
4. Names and namespaces
SDF definition files may contribute to a global namespace, and may
reference elements from that global namespace. (An SDF definition
file that does not set a defaultNamespace does not contribute to a
global namespace.)
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 versions 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.)
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 the present version of this specification, the query
part should not be used (it might be used in later versions).
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
definition file is constructed from a JSON pointer that selects the
element defined for this name in the SDF definition file.
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 definition file.
E.g., in Figure 1, definitions for the following global names are
contributed:
* https://example.com/capability/cap#/sdfObject/Switch
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* 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.
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 definition file 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
definition file, 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 definition file that does not set a default namespace.
Name references that point outside the current SDF definition file
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:
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* copying elements via sdfRef values
* pointing to elements via sdfRequired value elements
4.4. sdfRef
In a JSON map establishing a definition, the keyword "sdfRef" is used
to copy all of the qualities 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
[I-D.handrews-json-schema-validation].)
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. 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.
TODO: Make sure that the grammar in Appendix A allows specifying the
null values that are necessary to remove members in a merge-patch.
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4.5. sdfRequired
The keyword "sdfRequired" is provided to apply a constraint that
defines for which declarations corresponding data are mandatory in an
instance conforming the current definition.
The value of "sdfRequired" is an array of name references (JSON
pointers), each indicating one declaration that is 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
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.
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+=============+==============+===================================+
| Quality | Type | Description |
+=============+==============+===================================+
| description | text | long text (no constraints) |
+-------------+--------------+-----------------------------------+
| label | text | short text (no constraints) |
+-------------+--------------+-----------------------------------+
| $comment | text | source code comments only, no |
| | | semantics |
+-------------+--------------+-----------------------------------+
| sdfRef | sdf-pointer | (see Section 4.4) |
+-------------+--------------+-----------------------------------+
| sdfRequired | pointer-list | (see Section 4.5, applies to |
| | | qualities of properties, of data) |
+-------------+--------------+-----------------------------------+
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 |
+---------------+----------------+------------------------+---------+
| scaleMinimum | number | lower limit of value | N/A |
| | | in units given by | |
| | | unit (note 2) | |
+---------------+----------------+------------------------+---------+
| scaleMaximum | number | upper limit of value | N/A |
| | | in units given by | |
| | | unit (note 2) | |
+---------------+----------------+------------------------+---------+
| 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 | |
+---------------+----------------+------------------------+---------+
| sdfType | string | sdfType enumeration | N/A |
| | (Section | (extensible) | |
| | 4.7.1) | | |
+---------------+----------------+------------------------+---------+
| 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 SDF 1.0. 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
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processors are not expected to (and normally SHOULD NOT)
dereference these URIs; they may be useful to humans, though. A
URI unit name is distinguished from a registered unit name by the
presence of a colon; registered unit names that contain a colon
(at the time of writing, none) can therefore not be used in SDF.
For use by translators into ecosystems that require URIs for unit
names, the URN sub-namespace "urn:ietf:params:unit" is provided
(Section 7.2); URNs from this sub-namespace MUST NOT be used in a
unit quality, in favor of simply notating the unit name (e.g., kg
instead of urn:ietf:params:unit:kg).
2. these qualities were included in SDF 1.0, but were not fully
defined; they are not included in SDF 1.1. In 1.next, they will
be replaced by qualities to express scaling that are more aligned
with the processes that combine ecosystem and instance specific
information with an SDF model.
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 SDF.
To aid interworking with [I-D.handrews-json-schema-validation]
implementations, it is RECOMMENDED that sdfType is always used in
conjunction with the type quality inherited from
[I-D.handrews-json-schema-validation], in such a way as to yield a
common representation of the type's values in JSON.
Values for sdfType that are defined in SDF 1.1 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 SDF 1.1 for 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 future
versions of this specification.
In SDF 1.0, 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 JSON object
used to represent the choice) and a set of dataqualities (object, the
value in the JSON object used to represent the choice).
sdfChoice merges the functions of two constructs found in
[I-D.handrews-json-schema-validation]:
* enum
What would have been
"enum": ["foo", "bar", "baz"]
in SDF 1.0, 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,
e.g. what would have been
"type": "number",
"enum": [1, 2, 3]
in SDF 1.0, is represented as:
"type": "number",
"sdfChoice": {
"a-better-name-for-alternative-1": { "const": 1 },
"alternative-2": { "const": 2 },
"the-third-alternative": { "const": 3 }
}
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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, e.g., if the actual string value is indeed a crucial
element for the data model.)
* anyOf
[I-D.handrews-json-schema-validation] provides a type union called
anyOf, which provides a choice between anonymous alternatives.
What could have been
"anyOf": [
{"type": "array", "minItems": 3, "maxItems": "3", "items": {
"$ref": "#/sdfData/rgbVal"}},
{"type": "array", "minItems": 4, "maxItems": "4", "items": {
"$ref": "#/sdfData/cmykVal"}}
]
in [I-D.handrews-json-schema-validation] 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
[I-D.handrews-json-schema-validation].
As a simplification for readers of SDF specifications accustomed to
the [I-D.handrews-json-schema-validation] 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"}
}
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 Object
definitions. Object definitions may contain or include definitions
of Properties, Actions, Events declared for the object, as well as
data types (sdfData group) to be used in this or other Objects.
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 object |
+-------------+-----------+-----------------------------+
| sdfAction | action | zero or more named action |
| | | definitions for this object |
+-------------+-----------+-----------------------------+
| sdfEvent | event | zero or more named event |
| | | definitions for this object |
+-------------+-----------+-----------------------------+
| sdfData | named-sdq | zero or more named data |
| | | type definitions that might |
| | | be used in the above |
+-------------+-----------+-----------------------------+
| minItems | number | (array) Minimum number of |
| | | sdfObject instances in |
| | | array |
+-------------+-----------+-----------------------------+
| maxItems | number | (array) Maximum number of |
| | | sdfObject instances 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 Objects.
* The ability to compose a reusable definition block from Objects,
for example a single plug unit of an outlet strip with on/off
control, energy monitor, and optional dimmer objects, while
retaining the atomicity of the individual objects.
* The ability to compose Objects and other definition blocks into a
higher level thing that represents a product, while retaining the
atomicity of objects.
* The ability to enrich and refine a base definition to have
product-specific qualities and quality values, e.g. 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 definition files that are present in 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. There is expected to be an SDF namespace for
common SDF definitions used in OneDM.
The structure of a path in a namespace is defined by the JSON
Pointers to the definitions in the files in that namespace. For
example, if there is a file defining an object "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).
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6.2. Modular Composition
Modular composition of definitions enables an existing definition
(could be in the same file or another file) to become part of a new
definition by including a reference to the existing definition within
the model namespace.
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 (objects) do not have a defined order, so the
SDF processor may see these overrides before seeing the sdfRef.)
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 object declarations that
make up the definition of a single socket of an outlet strip could be
encapsulated in an sdfThing, and the socket-thing itself could be
used in a declaration in the sdfThing definition for the outlet
strip.
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.
The qualities of sdfThing are shown in Table 10.
+===========+========+=============+
| Quality | Type | Description |
+===========+========+=============+
| (common) | | Section 4.6 |
+-----------+--------+-------------+
| sdfThing | thing | |
+-----------+--------+-------------+
| sdfObject | object | |
+-----------+--------+-------------+
Table 10: Qualities of sdfThing
7. IANA Considerations
7.1. Media Type
IANA is requested to add the following Media-Type to the "Media
Types" registry.
+==========+======================+=======================+
| Name | Template | Reference |
+==========+======================+=======================+
| sdf+json | application/sdf+json | RFC XXXX, Section 7.1 |
+----------+----------------------+-----------------------+
Table 11
// RFC Ed.: please replace RFC XXXX with this RFC number and remove
this note.
Type name: application
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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
Fragment identifier considerations: A JSON Pointer fragment
identifier may be used, as defined in Section 6 of [RFC6901].
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. 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, 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".
7.3. Registries
(TBD: After future additions, check if we need any.)
8. Security Considerations
Some wider issues are discussed in [RFC8576].
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(Specifics: TBD.)
9. References
9.1. Normative References
[IANA.params]
IANA, "Uniform Resource Name (URN) Namespace for IETF
Use", <https://www.iana.org/assignments/params>.
[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/info/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/info/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/info/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/info/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/info/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/info/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/info/rfc6901>.
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[RFC7396] Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396,
DOI 10.17487/RFC7396, October 2014,
<https://www.rfc-editor.org/info/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/info/rfc8174>.
[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/info/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/info/rfc8610>.
[RFC8798] Bormann, C., "Additional Units for Sensor Measurement
Lists (SenML)", RFC 8798, DOI 10.17487/RFC8798, June 2020,
<https://www.rfc-editor.org/info/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/info/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/info/rfc9165>.
[SPDX] "SPDX License List", <https://spdx.org/licenses/>.
[W3C.NOTE-curie-20101216]
Birbeck, M. and S. McCarron, "CURIE Syntax 1.0", World
Wide Web Consortium NOTE NOTE-curie-20101216, 16 December
2010, <https://www.w3.org/TR/2010/NOTE-curie-20101216>.
9.2. Informative References
[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-jsonpath-iregexp]
Bormann, C., "I-Regexp: An Interoperable Regexp Format",
Work in Progress, Internet-Draft, draft-bormann-jsonpath-
iregexp-02, 17 January 2022,
<https://www.ietf.org/archive/id/draft-bormann-jsonpath-
iregexp-02.txt>.
[I-D.handrews-json-schema-validation]
Wright, A., Andrews, H., and B. Hutton, "JSON Schema
Validation: A Vocabulary for Structural Validation of
JSON", Work in Progress, Internet-Draft, draft-handrews-
json-schema-validation-02, 17 September 2019,
<https://www.ietf.org/archive/id/draft-handrews-json-
schema-validation-02.txt>.
[I-D.irtf-t2trg-rest-iot]
Keranen, 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-09, 26
February 2022, <https://www.ietf.org/archive/id/draft-
irtf-t2trg-rest-iot-09.txt>.
[I-D.wright-json-schema]
Wright, A. and H. Andrews, "JSON Schema: A Media Type for
Describing JSON Documents", Work in Progress, Internet-
Draft, draft-wright-json-schema-01, 16 April 2017,
<https://www.ietf.org/archive/id/draft-wright-json-schema-
01.txt>.
[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/info/rfc8576>.
[ZCL] "The ZigBee Cluster Library", 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>.
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Appendix A. Formal Syntax of SDF
This appendix describes the syntax of SDF using CDDL [RFC8610]. Note
that this appendix was derived from Ari Keranen's "alt-schema" and
Michael Koster's "schema", with a view of covering the syntax that is
currently in use at the One Data Model playground repository.
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.
This appendix makes use of CDDL "features" as defined in Section 4 of
[RFC9165]. A feature named "1.0" is used to indicate parts of the
syntax being deprecated towards SDF 1.1, and a feature named "1.1" is
used to indicate new syntax intended for SDF 1.1. Features whose
names end in "-ext" indicate extension points for further evolution.
start = sdf-syntax
sdf-syntax = {
? info: sdfinfo ; This will be required in most process policies, but not a syntax error
? namespace: named<text>
? defaultNamespace: text
? sdfThing: named<thingqualities> ; Thing is a composition of objects that work together in some way
? sdfProduct: named<productqualities> ; Product is a composition of things and objects that can model a SKU-level instance of a product
? sdfObject: named<objectqualities> ; Object is a set of Properties, Actions, and Events that together perform a particular function
? sdfProperty: named<propertyqualities> ; Property represents the state of an instance of an object
? sdfAction: named<actionqualities> ; Action is a directive to invoke an application layer verb associated with an object
? sdfEvent: named<eventqualities> ; Event represents an occurrence of something associated with an object
? sdfData: named<dataqualities> ; 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
EXTENSION-POINT<"top-ext">
}
sdfinfo = {
? title: text
? version: text
? copyright: text
? license: text
EXTENSION-POINT<"info-ext">
}
; Shortcut for a map that gives names to instances of X (has text keys and values of type X)
named<X> = { * text => X }
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EXTENSION-POINT<f> = ( * (text .feature f) => any ) ; only used in framework syntax
sdf-pointer = text ; .regexp curie-regexp -- TO DO!
pointer-list = [* sdf-pointer] ; ISSUE: no point in having an empty list, no? but used for sdfRequired in odmobject-multiple_axis_joystick.sdf.json
commonqualities = (
? description: text ; long text (no constraints)
? label: text ; short text (no constraints); default to key
? $comment: text ; source code comments only, no semantics
? sdfRef: sdf-pointer
? sdfRequired: pointer-list ; applies to qualities of properties, of data
)
; for building hierarchy
thingqualities = {
commonqualities
? sdfObject: named<objectqualities>
? sdfThing: named<thingqualities>
EXTENSION-POINT<"thing-ext">
}
productqualities = thingqualities ; ISSUE: get rid of sdfProduct?
; for single objects, or for arrays of objects (1.2)
objectqualities = {
commonqualities
? ("minItems" .feature "1.2") => number
? ("maxItems" .feature "1.2") => number
? sdfProperty: named<propertyqualities>
? sdfAction: named<actionqualities>
? sdfEvent: named<eventqualities>
? sdfData: named<dataqualities>
EXTENSION-POINT<"object-ext">
}
propertyqualities = dataqualities ; the definitions in sdfData are declarations in sdfProperty
parameter-list =
pointer-list .feature (["1.0", "pointerlist-as-parameter"]) /
dataqualities .feature (["1.1", "dataqualities-as-parameter"])
actionqualities = {
commonqualities
? sdfInputData: parameter-list ; sdfRequiredInputData applies here (a bit redundant)
? ("sdfRequiredInputData" .feature "1.0") => pointer-list
? sdfOutputData: parameter-list ; sdfRequired applies here
? sdfData: named<dataqualities> ; zero or more named data type definitions that might be used in the above
EXTENSION-POINT<"action-ext">
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}
eventqualities = {
commonqualities
? sdfOutputData: parameter-list ; sdfRequired applies here
? sdfData: named<dataqualities> ; zero or more named data type definitions that might be used in the above
EXTENSION-POINT<"event-ext">
}
dataqualities = { ; also propertyqualities
commonqualities
jsonschema
? ("units" .feature "1.0") => text
? ("unit" .feature "1.1") => text
? ("scaleMinimum" .feature "1.0") => number
? ("scaleMaximum" .feature "1.0") => number
? observable: bool
? readable: bool
? writable: bool
? nullable: bool
? ("subtype" .feature "1.0") => "byte-string" / "unix-time"
/ (text .feature "subtype-ext") ; EXTENSION-POINT
? ("sdfType" .feature "1.1") => "byte-string" / "unix-time"
/ (text .feature "sdftype-ext") ; EXTENSION-POINT
? contentFormat: text
EXTENSION-POINT<"data-ext">
}
allowed-types = number / text / bool / null
/ [* number] / [* text] / [* bool]
/ {* text => any}
/ (any .feature "allowed-ext") ; EXTENSION-POINT
compound-type = (
"type" => ("object" .feature "1.1")
? required: [+text]
? properties: named<dataqualities>
)
choice-type = (
("sdfChoice" .feature "1.1") => named<dataqualities>
)
jsonschema = (
? (("type" => "number" / "string" / "boolean" / "integer" / "array")
// compound-type
// choice-type
// (type: text .feature "type-ext") ; EXTENSION-POINT
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)
? "enum" => [+ text] ; limited to text strings in SDF 1.1
? ("enum" .feature "1.0") => [+ allowed-types] ; should validate against type
? const: allowed-types ; should validate against type
? default: allowed-types ; should validate against type
; number/integer constraints
? minimum: number
? maximum: number
? exclusiveMinimum: bool / number ; jso draft 4/7
? exclusiveMaximum: bool / number ; jso draft 4/7
? multipleOf: number ; ISSUE: Do we need this?
; text string constraints
? minLength: number
? maxLength: number
? pattern: text ; regexp
? format: "date-time" / "date" / "time"
/ "uri" / "uri-reference" / "uuid"
/ (text .feature "format-ext") ; EXTENSION-POINT
; array constraints
? minItems: number
? maxItems: number
? uniqueItems: bool
? items: { ;;; ultimately, this will be mostly recursive, but, for now
;;; let's find out what we actually need
? sdfRef: sdf-pointer ; import limited to the subset that we allow here...
? description: text ; long text (no constraints)
? $comment: text ; source code comments only, no semantics
; commonqualities, ; -- ISSUE: should leave this out for non-complex data types, but need the above three
? ((type: "number" / "string" / "boolean" / "integer") ; no "array"
// compound-type
// choice-type ; do we really need arrays of choices?
// (type: text .feature "itemtype-ext") ; EXTENSION-POINT
)
; jso subset
? minimum: number
? maximum: number
? "enum" => [+ text] ; limited to text strings in SDF 1.1
? ("enum" .feature "1.0") => [+ any]
? format: text
? minLength: number
? maxLength: number
EXTENSION-POINT<"items-ext">
}
)
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Appendix B. json-schema.org Rendition of SDF Syntax
This appendix describes the syntax of SDF defined in Appendix A, but
using a version of the description techniques advertised on json-
schema.org [I-D.handrews-json-schema-validation].
The appendix shows both the validation and the framework syntax.
Since most of the lines are the same between these two files, those
lines are shown only once, with a leading space, in the form of a
unified diff. Lines leading with a - are part of the validation
syntax, and lines leading with a + are part of the framework syntax.
{
- "title": "sdf-validation.cddl",
+ "title": "sdf-framework.cddl",
"$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": {
"$ref": "#/definitions/thingqualities"
}
},
"sdfProduct": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/productqualities"
}
},
"sdfObject": {
"type": "object",
"additionalProperties": {
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"$ref": "#/definitions/objectqualities"
}
},
"sdfProperty": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/propertyqualities"
}
},
"sdfAction": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/actionqualities"
}
},
"sdfEvent": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/eventqualities"
}
},
"sdfData": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/dataqualities"
}
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
},
"sdfinfo": {
"type": "object",
"properties": {
"title": {
"type": "string"
},
"version": {
"type": "string"
},
"copyright": {
"type": "string"
},
"license": {
"type": "string"
}
},
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- "additionalProperties": false
+ "additionalProperties": {
+ }
},
"thingqualities": {
"type": "object",
"properties": {
"description": {
"type": "string"
},
"label": {
"type": "string"
},
"$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"
}
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
},
"sdf-pointer": {
"type": "string"
},
"pointer-list": {
"type": "array",
"items": {
"$ref": "#/definitions/sdf-pointer"
}
},
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"objectqualities": {
"type": "object",
"properties": {
"description": {
"type": "string"
},
"label": {
"type": "string"
},
"$comment": {
"type": "string"
},
"sdfRef": {
"$ref": "#/definitions/sdf-pointer"
},
"sdfRequired": {
"$ref": "#/definitions/pointer-list"
},
"minItems": {
"type": "number"
},
"maxItems": {
"type": "number"
},
"sdfProperty": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/propertyqualities"
}
},
"sdfAction": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/actionqualities"
}
},
"sdfEvent": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/eventqualities"
}
},
"sdfData": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/dataqualities"
}
}
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},
- "additionalProperties": false
+ "additionalProperties": {
+ }
},
"propertyqualities": {
"$ref": "#/definitions/dataqualities"
},
"dataqualities": {
"anyOf": [
{
"type": "object",
"properties": {
"type": {
"type": "string",
"enum": [
"number",
"string",
"boolean",
"integer",
"array"
]
},
"enum": {
"type": "array",
"items": {
- "type": "string"
+ "$ref": "#/definitions/allowed-types"
},
"minItems": 1
},
"const": {
"$ref": "#/definitions/allowed-types"
},
"default": {
"$ref": "#/definitions/allowed-types"
},
"minimum": {
"type": "number"
},
"maximum": {
"type": "number"
},
"exclusiveMinimum": {
"anyOf": [
{
"type": "boolean"
},
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{
"type": "number"
}
]
},
"exclusiveMaximum": {
"anyOf": [
{
"type": "boolean"
},
{
"type": "number"
}
]
},
"multipleOf": {
"type": "number"
},
"minLength": {
"type": "number"
},
"maxLength": {
"type": "number"
},
"pattern": {
"type": "string"
},
"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"
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+ },
+ {
+ "type": "string",
+ "const": "uri"
+ },
+ {
+ "type": "string",
+ "const": "uri-reference"
+ },
+ {
+ "type": "string",
+ "const": "uuid"
+ },
+ {
+ "type": "string"
+ }
]
},
"minItems": {
"type": "number"
},
"maxItems": {
"type": "number"
},
"uniqueItems": {
"type": "boolean"
},
"items": {
"anyOf": [
{
"type": "object",
"properties": {
"type": {
"type": "string",
"enum": [
"number",
"string",
"boolean",
"integer"
]
},
"sdfRef": {
"$ref": "#/definitions/sdf-pointer"
},
"description": {
"type": "string"
},
"$comment": {
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"type": "string"
},
"minimum": {
"type": "number"
},
"maximum": {
"type": "number"
},
"enum": {
"type": "array",
- "items": {
- "type": "string"
- },
"minItems": 1
},
"format": {
"type": "string"
},
"minLength": {
"type": "number"
},
"maxLength": {
"type": "number"
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
},
{
"type": "object",
"properties": {
"type": {
"type": "string",
"const": "object"
},
"required": {
"type": "array",
"items": {
"type": "string"
},
"minItems": 1
},
"properties": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/dataqualities"
}
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},
"sdfRef": {
"$ref": "#/definitions/sdf-pointer"
},
"description": {
"type": "string"
},
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"type": "string"
},
"minimum": {
"type": "number"
},
"maximum": {
"type": "number"
},
"enum": {
"type": "array",
- "items": {
- "type": "string"
- },
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"format": {
"type": "string"
},
"minLength": {
"type": "number"
},
"maxLength": {
"type": "number"
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
},
{
"type": "object",
"properties": {
"sdfChoice": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/dataqualities"
}
},
"sdfRef": {
"$ref": "#/definitions/sdf-pointer"
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},
"description": {
"type": "string"
},
"$comment": {
"type": "string"
},
"minimum": {
"type": "number"
},
"maximum": {
"type": "number"
},
"enum": {
"type": "array",
- "items": {
- "type": "string"
- },
"minItems": 1
},
"format": {
"type": "string"
},
"minLength": {
"type": "number"
},
"maxLength": {
"type": "number"
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
+ },
+ {
+ "type": "object",
+ "properties": {
+ "type": {
+ "type": "string"
+ },
+ "sdfRef": {
+ "$ref": "#/definitions/sdf-pointer"
+ },
+ "description": {
+ "type": "string"
+ },
+ "$comment": {
+ "type": "string"
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+ },
+ "minimum": {
+ "type": "number"
+ },
+ "maximum": {
+ "type": "number"
+ },
+ "enum": {
+ "type": "array",
+ "minItems": 1
+ },
+ "format": {
+ "type": "string"
+ },
+ "minLength": {
+ "type": "number"
+ },
+ "maxLength": {
+ "type": "number"
+ }
+ },
+ "additionalProperties": {
+ }
}
]
},
"description": {
"type": "string"
},
"label": {
"type": "string"
},
"$comment": {
"type": "string"
},
"sdfRef": {
"$ref": "#/definitions/sdf-pointer"
},
"sdfRequired": {
"$ref": "#/definitions/pointer-list"
},
+ "units": {
+ "type": "string"
+ },
"unit": {
"type": "string"
},
+ "scaleMinimum": {
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+ "type": "number"
+ },
+ "scaleMaximum": {
+ "type": "number"
+ },
"observable": {
"type": "boolean"
},
"readable": {
"type": "boolean"
},
"writable": {
"type": "boolean"
},
"nullable": {
"type": "boolean"
},
+ "subtype": {
+ "anyOf": [
+ {
+ "type": "string",
+ "const": "byte-string"
+ },
+ {
+ "type": "string",
+ "const": "unix-time"
+ },
+ {
+ "type": "string"
+ }
+ ]
+ },
"sdfType": {
- "type": "string",
- "enum": [
- "byte-string",
- "unix-time"
+ "anyOf": [
+ {
+ "type": "string",
+ "const": "byte-string"
+ },
+ {
+ "type": "string",
+ "const": "unix-time"
+ },
+ {
+ "type": "string"
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+ }
]
},
"contentFormat": {
"type": "string"
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
},
{
"type": "object",
"properties": {
"type": {
"type": "string",
"const": "object"
},
"required": {
"type": "array",
"items": {
"type": "string"
},
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},
"properties": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/dataqualities"
}
},
"enum": {
"type": "array",
"items": {
- "type": "string"
+ "$ref": "#/definitions/allowed-types"
},
"minItems": 1
},
"const": {
"$ref": "#/definitions/allowed-types"
},
"default": {
"$ref": "#/definitions/allowed-types"
},
"minimum": {
"type": "number"
},
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"maximum": {
"type": "number"
},
"exclusiveMinimum": {
"anyOf": [
{
"type": "boolean"
},
{
"type": "number"
}
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{
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},
{
"type": "number"
}
]
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"multipleOf": {
"type": "number"
},
"minLength": {
"type": "number"
},
"maxLength": {
"type": "number"
},
"pattern": {
"type": "string"
},
"format": {
- "type": "string",
- "enum": [
- "date-time",
- "date",
- "time",
- "uri",
- "uri-reference",
- "uuid"
+ "anyOf": [
+ {
+ "type": "string",
+ "const": "date-time"
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+ },
+ {
+ "type": "string",
+ "const": "date"
+ },
+ {
+ "type": "string",
+ "const": "time"
+ },
+ {
+ "type": "string",
+ "const": "uri"
+ },
+ {
+ "type": "string",
+ "const": "uri-reference"
+ },
+ {
+ "type": "string",
+ "const": "uuid"
+ },
+ {
+ "type": "string"
+ }
]
},
"minItems": {
"type": "number"
},
"maxItems": {
"type": "number"
},
"uniqueItems": {
"type": "boolean"
},
"items": {
"anyOf": [
{
"type": "object",
"properties": {
"type": {
"type": "string",
"enum": [
"number",
"string",
"boolean",
"integer"
]
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},
"sdfRef": {
"$ref": "#/definitions/sdf-pointer"
},
"description": {
"type": "string"
},
"$comment": {
"type": "string"
},
"minimum": {
"type": "number"
},
"maximum": {
"type": "number"
},
"enum": {
"type": "array",
- "items": {
- "type": "string"
- },
"minItems": 1
},
"format": {
"type": "string"
},
"minLength": {
"type": "number"
},
"maxLength": {
"type": "number"
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
},
{
"type": "object",
"properties": {
"type": {
"type": "string",
"const": "object"
},
"required": {
"type": "array",
"items": {
"type": "string"
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},
"minItems": 1
},
"properties": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/dataqualities"
}
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"description": {
"type": "string"
},
"$comment": {
"type": "string"
},
"minimum": {
"type": "number"
},
"maximum": {
"type": "number"
},
"enum": {
"type": "array",
- "items": {
- "type": "string"
- },
"minItems": 1
},
"format": {
"type": "string"
},
"minLength": {
"type": "number"
},
"maxLength": {
"type": "number"
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
},
{
"type": "object",
"properties": {
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"sdfChoice": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/dataqualities"
}
},
"sdfRef": {
"$ref": "#/definitions/sdf-pointer"
},
"description": {
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},
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"type": "string"
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"minimum": {
"type": "number"
},
"maximum": {
"type": "number"
},
"enum": {
"type": "array",
- "items": {
- "type": "string"
- },
"minItems": 1
},
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"type": "string"
},
"minLength": {
"type": "number"
},
"maxLength": {
"type": "number"
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
+ },
+ {
+ "type": "object",
+ "properties": {
+ "type": {
+ "type": "string"
+ },
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+ "sdfRef": {
+ "$ref": "#/definitions/sdf-pointer"
+ },
+ "description": {
+ "type": "string"
+ },
+ "$comment": {
+ "type": "string"
+ },
+ "minimum": {
+ "type": "number"
+ },
+ "maximum": {
+ "type": "number"
+ },
+ "enum": {
+ "type": "array",
+ "minItems": 1
+ },
+ "format": {
+ "type": "string"
+ },
+ "minLength": {
+ "type": "number"
+ },
+ "maxLength": {
+ "type": "number"
+ }
+ },
+ "additionalProperties": {
+ }
}
]
},
"description": {
"type": "string"
},
"label": {
"type": "string"
},
"$comment": {
"type": "string"
},
"sdfRef": {
"$ref": "#/definitions/sdf-pointer"
},
"sdfRequired": {
"$ref": "#/definitions/pointer-list"
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},
+ "units": {
+ "type": "string"
+ },
"unit": {
"type": "string"
},
+ "scaleMinimum": {
+ "type": "number"
+ },
+ "scaleMaximum": {
+ "type": "number"
+ },
"observable": {
"type": "boolean"
},
"readable": {
"type": "boolean"
},
"writable": {
"type": "boolean"
},
"nullable": {
"type": "boolean"
},
+ "subtype": {
+ "anyOf": [
+ {
+ "type": "string",
+ "const": "byte-string"
+ },
+ {
+ "type": "string",
+ "const": "unix-time"
+ },
+ {
+ "type": "string"
+ }
+ ]
+ },
"sdfType": {
- "type": "string",
- "enum": [
- "byte-string",
- "unix-time"
+ "anyOf": [
+ {
+ "type": "string",
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+ "const": "byte-string"
+ },
+ {
+ "type": "string",
+ "const": "unix-time"
+ },
+ {
+ "type": "string"
+ }
]
},
"contentFormat": {
"type": "string"
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
},
{
"type": "object",
"properties": {
"sdfChoice": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/dataqualities"
}
},
"enum": {
"type": "array",
"items": {
- "type": "string"
+ "$ref": "#/definitions/allowed-types"
},
"minItems": 1
},
"const": {
"$ref": "#/definitions/allowed-types"
},
"default": {
"$ref": "#/definitions/allowed-types"
},
"minimum": {
"type": "number"
},
"maximum": {
"type": "number"
},
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"exclusiveMinimum": {
"anyOf": [
{
"type": "boolean"
},
{
"type": "number"
}
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},
"exclusiveMaximum": {
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{
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},
{
"type": "number"
}
]
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"multipleOf": {
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},
"minLength": {
"type": "number"
},
"maxLength": {
"type": "number"
},
"pattern": {
"type": "string"
},
"format": {
- "type": "string",
- "enum": [
- "date-time",
- "date",
- "time",
- "uri",
- "uri-reference",
- "uuid"
+ "anyOf": [
+ {
+ "type": "string",
+ "const": "date-time"
+ },
+ {
+ "type": "string",
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+ "const": "date"
+ },
+ {
+ "type": "string",
+ "const": "time"
+ },
+ {
+ "type": "string",
+ "const": "uri"
+ },
+ {
+ "type": "string",
+ "const": "uri-reference"
+ },
+ {
+ "type": "string",
+ "const": "uuid"
+ },
+ {
+ "type": "string"
+ }
]
},
"minItems": {
"type": "number"
},
"maxItems": {
"type": "number"
},
"uniqueItems": {
"type": "boolean"
},
"items": {
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{
"type": "object",
"properties": {
"type": {
"type": "string",
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"number",
"string",
"boolean",
"integer"
]
},
"sdfRef": {
"$ref": "#/definitions/sdf-pointer"
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},
"description": {
"type": "string"
},
"$comment": {
"type": "string"
},
"minimum": {
"type": "number"
},
"maximum": {
"type": "number"
},
"enum": {
"type": "array",
- "items": {
- "type": "string"
- },
"minItems": 1
},
"format": {
"type": "string"
},
"minLength": {
"type": "number"
},
"maxLength": {
"type": "number"
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
},
{
"type": "object",
"properties": {
"type": {
"type": "string",
"const": "object"
},
"required": {
"type": "array",
"items": {
"type": "string"
},
"minItems": 1
},
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"properties": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/dataqualities"
}
},
"sdfRef": {
"$ref": "#/definitions/sdf-pointer"
},
"description": {
"type": "string"
},
"$comment": {
"type": "string"
},
"minimum": {
"type": "number"
},
"maximum": {
"type": "number"
},
"enum": {
"type": "array",
- "items": {
- "type": "string"
- },
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},
"format": {
"type": "string"
},
"minLength": {
"type": "number"
},
"maxLength": {
"type": "number"
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
},
{
"type": "object",
"properties": {
"sdfChoice": {
"type": "object",
"additionalProperties": {
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"$ref": "#/definitions/dataqualities"
}
},
"sdfRef": {
"$ref": "#/definitions/sdf-pointer"
},
"description": {
"type": "string"
},
"$comment": {
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},
"minimum": {
"type": "number"
},
"maximum": {
"type": "number"
},
"enum": {
"type": "array",
- "items": {
- "type": "string"
- },
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},
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"type": "string"
},
"minLength": {
"type": "number"
},
"maxLength": {
"type": "number"
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
+ },
+ {
+ "type": "object",
+ "properties": {
+ "type": {
+ "type": "string"
+ },
+ "sdfRef": {
+ "$ref": "#/definitions/sdf-pointer"
+ },
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+ "description": {
+ "type": "string"
+ },
+ "$comment": {
+ "type": "string"
+ },
+ "minimum": {
+ "type": "number"
+ },
+ "maximum": {
+ "type": "number"
+ },
+ "enum": {
+ "type": "array",
+ "minItems": 1
+ },
+ "format": {
+ "type": "string"
+ },
+ "minLength": {
+ "type": "number"
+ },
+ "maxLength": {
+ "type": "number"
+ }
+ },
+ "additionalProperties": {
+ }
}
]
},
"description": {
"type": "string"
},
"label": {
"type": "string"
},
"$comment": {
"type": "string"
},
"sdfRef": {
"$ref": "#/definitions/sdf-pointer"
},
"sdfRequired": {
"$ref": "#/definitions/pointer-list"
},
+ "units": {
+ "type": "string"
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+ },
"unit": {
"type": "string"
},
+ "scaleMinimum": {
+ "type": "number"
+ },
+ "scaleMaximum": {
+ "type": "number"
+ },
"observable": {
"type": "boolean"
},
"readable": {
"type": "boolean"
},
"writable": {
"type": "boolean"
},
"nullable": {
"type": "boolean"
},
- "sdfType": {
- "type": "string",
- "enum": [
- "byte-string",
- "unix-time"
- ]
- },
+ "subtype": {
+ "anyOf": [
+ {
+ "type": "string",
+ "const": "byte-string"
+ },
+ {
+ "type": "string",
+ "const": "unix-time"
+ },
+ {
+ "type": "string"
+ }
+ ]
+ },
+ "sdfType": {
+ "anyOf": [
+ {
+ "type": "string",
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+ "const": "byte-string"
+ },
+ {
+ "type": "string",
+ "const": "unix-time"
+ },
+ {
+ "type": "string"
+ }
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"contentFormat": {
"type": "string"
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
+ },
+ {
+ "type": "object",
+ "properties": {
+ "type": {
+ "type": "string"
+ },
+ "enum": {
+ "type": "array",
+ "items": {
+ "$ref": "#/definitions/allowed-types"
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+ "minItems": 1
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+ "const": {
+ "$ref": "#/definitions/allowed-types"
+ },
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+ "$ref": "#/definitions/allowed-types"
+ },
+ "minimum": {
+ "type": "number"
+ },
+ "maximum": {
+ "type": "number"
+ },
+ "exclusiveMinimum": {
+ "anyOf": [
+ {
+ "type": "boolean"
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+ },
+ {
+ "type": "number"
+ }
+ ]
+ },
+ "exclusiveMaximum": {
+ "anyOf": [
+ {
+ "type": "boolean"
+ },
+ {
+ "type": "number"
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+ "type": "number"
+ },
+ "minLength": {
+ "type": "number"
+ },
+ "maxLength": {
+ "type": "number"
+ },
+ "pattern": {
+ "type": "string"
+ },
+ "format": {
+ "anyOf": [
+ {
+ "type": "string",
+ "const": "date-time"
+ },
+ {
+ "type": "string",
+ "const": "date"
+ },
+ {
+ "type": "string",
+ "const": "time"
+ },
+ {
+ "type": "string",
+ "const": "uri"
+ },
+ {
+ "type": "string",
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+ "const": "uri-reference"
+ },
+ {
+ "type": "string",
+ "const": "uuid"
+ },
+ {
+ "type": "string"
+ }
+ ]
+ },
+ "minItems": {
+ "type": "number"
+ },
+ "maxItems": {
+ "type": "number"
+ },
+ "uniqueItems": {
+ "type": "boolean"
+ },
+ "items": {
+ "anyOf": [
+ {
+ "type": "object",
+ "properties": {
+ "type": {
+ "type": "string",
+ "enum": [
+ "number",
+ "string",
+ "boolean",
+ "integer"
+ ]
+ },
+ "sdfRef": {
+ "$ref": "#/definitions/sdf-pointer"
+ },
+ "description": {
+ "type": "string"
+ },
+ "$comment": {
+ "type": "string"
+ },
+ "minimum": {
+ "type": "number"
+ },
+ "maximum": {
+ "type": "number"
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+ },
+ "enum": {
+ "type": "array",
+ "minItems": 1
+ },
+ "format": {
+ "type": "string"
+ },
+ "minLength": {
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+ "maxLength": {
+ "type": "number"
+ }
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+ "additionalProperties": {
+ }
+ },
+ {
+ "type": "object",
+ "properties": {
+ "type": {
+ "type": "string",
+ "const": "object"
+ },
+ "required": {
+ "type": "array",
+ "items": {
+ "type": "string"
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+ "minItems": 1
+ },
+ "properties": {
+ "type": "object",
+ "additionalProperties": {
+ "$ref": "#/definitions/dataqualities"
+ }
+ },
+ "sdfRef": {
+ "$ref": "#/definitions/sdf-pointer"
+ },
+ "description": {
+ "type": "string"
+ },
+ "$comment": {
+ "type": "string"
+ },
+ "minimum": {
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+ "type": "number"
+ },
+ "maximum": {
+ "type": "number"
+ },
+ "enum": {
+ "type": "array",
+ "minItems": 1
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+ "maxLength": {
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+ }
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+ "additionalProperties": {
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+ },
+ {
+ "type": "object",
+ "properties": {
+ "sdfChoice": {
+ "type": "object",
+ "additionalProperties": {
+ "$ref": "#/definitions/dataqualities"
+ }
+ },
+ "sdfRef": {
+ "$ref": "#/definitions/sdf-pointer"
+ },
+ "description": {
+ "type": "string"
+ },
+ "$comment": {
+ "type": "string"
+ },
+ "minimum": {
+ "type": "number"
+ },
+ "maximum": {
+ "type": "number"
+ },
+ "enum": {
+ "type": "array",
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+ "minItems": 1
+ },
+ "format": {
+ "type": "string"
+ },
+ "minLength": {
+ "type": "number"
+ },
+ "maxLength": {
+ "type": "number"
+ }
+ },
+ "additionalProperties": {
+ }
+ },
+ {
+ "type": "object",
+ "properties": {
+ "type": {
+ "type": "string"
+ },
+ "sdfRef": {
+ "$ref": "#/definitions/sdf-pointer"
+ },
+ "description": {
+ "type": "string"
+ },
+ "$comment": {
+ "type": "string"
+ },
+ "minimum": {
+ "type": "number"
+ },
+ "maximum": {
+ "type": "number"
+ },
+ "enum": {
+ "type": "array",
+ "minItems": 1
+ },
+ "format": {
+ "type": "string"
+ },
+ "minLength": {
+ "type": "number"
+ },
+ "maxLength": {
+ "type": "number"
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+ }
+ },
+ "additionalProperties": {
+ }
+ }
+ ]
+ },
+ "description": {
+ "type": "string"
+ },
+ "label": {
+ "type": "string"
+ },
+ "$comment": {
+ "type": "string"
+ },
+ "sdfRef": {
+ "$ref": "#/definitions/sdf-pointer"
+ },
+ "sdfRequired": {
+ "$ref": "#/definitions/pointer-list"
+ },
+ "units": {
+ "type": "string"
+ },
+ "unit": {
+ "type": "string"
+ },
+ "scaleMinimum": {
+ "type": "number"
+ },
+ "scaleMaximum": {
+ "type": "number"
+ },
+ "observable": {
+ "type": "boolean"
+ },
+ "readable": {
+ "type": "boolean"
+ },
+ "writable": {
+ "type": "boolean"
+ },
+ "nullable": {
+ "type": "boolean"
+ },
+ "subtype": {
+ "anyOf": [
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+ {
+ "type": "string",
+ "const": "byte-string"
+ },
+ {
+ "type": "string",
+ "const": "unix-time"
+ },
+ {
+ "type": "string"
+ }
+ ]
+ },
+ "sdfType": {
+ "anyOf": [
+ {
+ "type": "string",
+ "const": "byte-string"
+ },
+ {
+ "type": "string",
+ "const": "unix-time"
+ },
+ {
+ "type": "string"
+ }
+ ]
+ },
+ "contentFormat": {
+ "type": "string"
+ }
+ },
+ "additionalProperties": {
+ }
}
]
},
"allowed-types": {
"anyOf": [
{
"type": "number"
},
{
"type": "string"
},
{
"type": "boolean"
},
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{
"type": "null"
},
{
"type": "array",
"items": {
"type": "number"
}
},
{
"type": "array",
"items": {
"type": "string"
}
},
{
"type": "array",
"items": {
"type": "boolean"
}
},
{
"type": "object",
"additionalProperties": {
}
+ },
+ {
}
]
},
"actionqualities": {
"type": "object",
"properties": {
"description": {
"type": "string"
},
"label": {
"type": "string"
},
"$comment": {
"type": "string"
},
"sdfRef": {
"$ref": "#/definitions/sdf-pointer"
},
"sdfRequired": {
"$ref": "#/definitions/pointer-list"
},
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"sdfInputData": {
"$ref": "#/definitions/parameter-list"
},
+ "sdfRequiredInputData": {
+ "$ref": "#/definitions/pointer-list"
+ },
"sdfOutputData": {
"$ref": "#/definitions/parameter-list"
},
"sdfData": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/dataqualities"
}
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
},
"parameter-list": {
- "$ref": "#/definitions/dataqualities"
+ "anyOf": [
+ {
+ "$ref": "#/definitions/pointer-list"
+ },
+ {
+ "$ref": "#/definitions/dataqualities"
+ }
+ ]
},
"eventqualities": {
"type": "object",
"properties": {
"description": {
"type": "string"
},
"label": {
"type": "string"
},
"$comment": {
"type": "string"
},
"sdfRef": {
"$ref": "#/definitions/sdf-pointer"
},
"sdfRequired": {
"$ref": "#/definitions/pointer-list"
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},
"sdfOutputData": {
"$ref": "#/definitions/parameter-list"
},
"sdfData": {
"type": "object",
"additionalProperties": {
"$ref": "#/definitions/dataqualities"
}
}
},
- "additionalProperties": false
+ "additionalProperties": {
+ }
},
"productqualities": {
"$ref": "#/definitions/thingqualities"
}
}
}
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 [I-D.handrews-json-schema-validation].
As the vocabulary used by JSO is familiar to many JSON modellers, 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).
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 something.
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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 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 are available in JSON.
The length (as measured in characters) can be constrained by the
additional data qualities "minLength" and "maxLength", which are
inclusive bounds. Note that the previous version of the present
document 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 restored).
The data quality "pattern" takes a string value that is interpreted
as an [ECMA-262] regular expression in Unicode mode that constrain
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 $).
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Note that this subset is somewhat similar to the subset introduced by
iregexps [I-D.bormann-jsonpath-iregexp], 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.
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 ("objects").
The additional quality "properties" is a map the entries of which
describe entries in the specified JSON object: The key gives an
allowable map key for the specified JSON object, and the value is a
map with a named set of data qualities giving the type for the
corresponding value in the specified JSON object.
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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.
E.g., [OCF] is based on Swagger 2.0 which appears to be based on
"draft-4" [I-D.wright-json-schema] (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.
TBD: add any useful implementation notes we can find for other
ecosystems that use JSO.
Acknowledgements
This draft 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
Ari Keränen
Ericsson
FI-02420 Jorvas
Finland
Email: ari.keranen@ericsson.com
Wouter van der Beek
Cascoda Ltd.
Threefield House
Threefield Lane
Southampton
United Kingdom
Email: w.vanderbeek@cascoda.com
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Authors' Addresses
Michael Koster (editor)
PassiveLogic
524 H Street
Antioch, CA, 94509
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
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