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Versions: 00                                                            
T2TRG                                                    C. Bormann, Ed.
Internet-Draft                                    Universität Bremen TZI
Intended status: Informational                              7 March 2021
Expires: 8 September 2021


 Semantic Definition Format (SDF) for Data and Interactions of Things:
                            Compact Notation
                   draft-bormann-asdf-sdf-compact-00

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.

   The SDF format is mainly intended for interchange between machine
   generation and machine processing.  However, there often is a need
   for humans to look at and edit SDF models.

   Similar to the way Relax-NG as defined in ISO/IEC 19757-2 has an XML
   format and a compact format (Annex C), this specification defines a
   compact format to go along SDF's JSON format.

   The present version of this document is mostly a proof of concept,
   but was deemed useful to obtain initial feedback on the approach
   taken.

Contributing

   Recent versions of this document are available at its GitHub
   repository https://github.com/cabo/sdfc (https://github.com/cabo/
   sdfc) -- this also provides an issue tracker as well as a way to
   supply "pull requests".

   General discussion of this SDF Internet-Draft happens on the mailing
   list of the IETF ASDF Working Group, asdf@ietf.org (subscribe at
   https://www.ietf.org/mailman/listinfo/asdf
   (https://www.ietf.org/mailman/listinfo/asdf)).

   The IETF Note Well applies (https://www.ietf.org/about/note-well/
   (https://www.ietf.org/about/note-well/)).






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Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 8 September 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Example Definition  . . . . . . . . . . . . . . . . . . .   4
   3.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     3.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Appendix A.  Example in SDF JSON format . . . . . . . . . . . . .   5
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   (See Abstract for now.)  [I-D.ietf-asdf-sdf] [RELAXNG]





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   The intention is to be able to bidirectionally translate between
   compact and JSON form, without appreciable semantic losses.  This
   will allow viewing SDF in compact form, apply edits if needed, and
   then continuing processing it in JSON form.  As a limitation of this
   approach, it will be difficult to always recreate the order of map
   entries (members of JSON objects) in the JSON form; this order is
   essentially arbitrary as maps (JSON objects) in JSON are unordered.
   (In the long run, it may be useful to define a canonical order in the
   SDF specification or here.)

   An initial prototype of a converter from compact form to JSON form
   was constructed during the ASDF/WISHI hackathon preceding IETF110.  A
   more complete, bidirectionally operating version of this tool is
   planned for release in week 12 of 2021.

2.  Overview

   The SDF compact format is a YAML file [YAML]; a good part of the work
   needed for a compact representation is already done by the increased
   user-friendliness of YAML over JSON.

   In addition, all the sections defined with "named<...>" in the CDDL
   definition of SDF have been compacted into map entries with space-
   separated keys, giving the kind first and the name next.  This saves
   the need for another level of hierarchy and reminds the reader of the
   kind of item being specified.

   The map key "description" is replaced by ":", which also is rendered
   in the most compact form possible in YAML.

   The dataqualities readable, writable, and observable, together with
   optionality, are compressed into a four-character map key: The first
   three are translated into "rwo" when set (default in SDF) and into
   "---" when not set.  The fourth character is "?" for optional and "!"
   for required.

   The value of this abbreviated key is a CDDL [RFC8610] rendition of
   the attributes defined in the jsonschema production in Appendix A of
   [I-D.ietf-asdf-sdf].  To further reduce noise, a top-level array
   production in the CDDL can be represented as an array in the YAML
   (i.e., does not require additional quotes).










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2.1.  Example Definition

   This is an SDF-compact version of a slightly modified copy of the
   sdfobject-cadence.sdf.json model found at the time of writing in
   OneDM's SDF playground.  (This example was chosen more or less
   randomly; better examples can probably be found.  The modification is
   the addition of a "unit" quality.)

   info:
     copyright: Copyright 2018-2019 Open Connectivity Foundation, Inc. All rights reserved.
     version: '2019-06-11'
     title: Cadence
     license: https://github.com/one-data-model/oneDM/blob/master/LICENSE

   object cadence:
     :: This Resource describes the cadence, which is the number of
        revolutions of crank per minute when cyclists pedal the
        pedals. The unit, which is the default unit, is rpm. The cadence
        Property is a read-only value that is provided by the
        server. When range (from "oic. r. baseresource") is omitted the
        default is 0 to +MAXFLOAT.
     property cadence:
       r-o!: integer .ge 0
       unit: 1/min
       :: This Property describes the rate at which a cyclist is pedalling/turning
          the pedals.
     property range:
       r-o?: [2*2 integer]
       :: The valid range for the Property in the Resource as an integer.
          The first value in the array is the minimum value, the second value in the
          array is the maximum value.
     property step:
       r-o?: integer
       :: Step value across the defined range when the range is an integer.  This
          is the increment for valid values across the range; so if range is 0..10
          and step is 2 then valid values are 0,2,4,6,8,10.

   The result of automatically converting this YAML file using the
   prototype "sdfc" tool back into the JSON form of SDF is given in
   Appendix A.  Except for the "unit" addition, it is semantically
   identical to the sdfobject-cadence.sdf.json.  Differences are visible
   in the order of map entries (members in JSON objects); a future
   version of the "sdfc" tool could attempt to preserve more of this
   order, even though it does not carry semantics.

3.  References

3.1.  Normative References



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   [I-D.ietf-asdf-sdf]
              Koster, M. and C. Bormann, "Semantic Definition Format
              (SDF) for Data and Interactions of Things", Work in
              Progress, Internet-Draft, draft-ietf-asdf-sdf-03, 22
              February 2021, <https://www.ietf.org/archive/id/draft-
              ietf-asdf-sdf-03.txt>.

   [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>.

3.2.  Informative References

   [RELAXNG]  ISO/IEC, "Information technology — Document Schema
              Definition Language (DSDL) — Part 2: Regular-grammar-based
              validation — RELAX NG", ISO/IEC 19757-2, 15 December 2008.

   [YAML]     Ben-Kiki, O., Evans, C., and I.d. Net, "YAML Ain't Markup
              Language (YAML[TM]) Version 1.2", 3rd Edition, October
              2009, <http://www.yaml.org/spec/1.2/spec.html>.

Appendix A.  Example in SDF JSON format



























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   {
     "info": {
       "title": "Cadence",
       "license": "https://github.com/one-data-model/oneDM/blob/master/LICENSE",
       "version": "2019-06-11",
       "copyright": "Copyright 2018-2019 Open Connectivity Foundation, Inc. All rights reserved."
     },
     "sdfObject": {
       "cadence": {
         "description": "This Resource describes the cadence, which is the number of revolutions of crank per minute when cyclists pedal the pedals. The unit, which is the default unit, is rpm. The cadence Property is a read-only value that is provided by the server. When range (from \"oic. r. baseresource\") is omitted the default is 0 to +MAXFLOAT.",
         "sdfProperty": {
           "step": {
             "type": "integer",
             "writable": false,
             "description": "Step value across the defined range when the range is an integer.  This is the increment for valid values across the range; so if range is 0..10 and step is 2 then valid values are 0,2,4,6,8,10."
           },
           "range": {
             "type": "array",
             "items": {
               "type": "integer"
             },
             "maxItems": 2,
             "minItems": 2,
             "writable": false,
             "description": "The valid range for the Property in the Resource as an integer. The first value in the array is the minimum value, the second value in the array is the maximum value."
           },
           "cadence": {
             "type": "integer",
             "minimum": 0,
             "writable": false,
             "description": "This Property describes the rate at which a cyclist is pedalling/turning the pedals."
           }
         },
         "sdfRequired": [
           "#/sdfObject/cadence/sdfProperty/cadence"
         ]
       }
     }
   }

Acknowledgements

   The idea for this draft originated at the IETF110 ASDF/WISHI
   hackathon.  The author would like to thank the attendees for initial
   feedback.

Author's Address




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   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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