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.
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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
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Please review these documents carefully, as they describe your rights
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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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