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Semantic Definition Format (SDF) for Data and Interactions of Things: Compact Notation
draft-bormann-asdf-sdf-compact-02

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Document	Type	Active Internet-Draft (individual)
	Author	Carsten Bormann
	Last updated	2022-02-28
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draft-bormann-asdf-sdf-compact-02

T2TRG C. Bormann, Ed.
Internet-Draft Universität Bremen TZI
Intended status: Informational 28 February 2022
Expires: 1 September 2022

Semantic Definition Format (SDF) for Data and Interactions of Things:
Compact Notation
draft-bormann-asdf-sdf-compact-02

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 is often 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.

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-bormann-asdf-sdf-compact/.

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/.

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 1 September 2022.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Example Definition . . . . . . . . . . . . . . . . . . . 4
3. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Normative References . . . . . . . . . . . . . . . . . . 5
3.2. Informative References . . . . . . . . . . . . . . . . . 5
Appendix A. Example in SDF JSON format . . . . . . . . . . . . . 5
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7

1. Introduction

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The SDF format is mainly intended for interchange between machine
generation and machine processing. However, there is often 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.

(References: [I-D.ietf-asdf-sdf], [RELAXNG].)

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 soon.

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.

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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).

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.

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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

[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-10, 16
January 2022, <https://www.ietf.org/archive/id/draft-ietf-
asdf-sdf-10.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. dot Net, "YAML Ain't
Markup Language (YAML™) version 1.2", Revision 1.2.2, 1
October 2021, <https://yaml.org/spec/1.2.2/>.

Appendix A. Example in SDF JSON format

=============== NOTE: '\' line wrapping per RFC 8792 ================

{
"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."
},

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"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"
]
}
}
}

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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

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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Semantic Definition Format (SDF) for Data and Interactions of Things: Compact Notation draft-bormann-asdf-sdf-compact-02

Semantic Definition Format (SDF) for Data and Interactions of Things: Compact Notation
draft-bormann-asdf-sdf-compact-02