Semantic Definition Format (SDF) for Data and Interactions of Things: Compact Notation
draft-bormann-asdf-sdf-compact-06
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Carsten Bormann | ||
| Last updated | 2024-04-25 | ||
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draft-bormann-asdf-sdf-compact-06
T2TRG C. Bormann, Ed.
Internet-Draft Universität Bremen TZI
Intended status: Informational 25 April 2024
Expires: 27 October 2024
Semantic Definition Format (SDF) for Data and Interactions of Things:
Compact Notation
draft-bormann-asdf-sdf-compact-06
Abstract
The Semantic Definition Format (SDF) is a format for domain experts
to use in the creation and maintenance of data and interaction models
that describe Things, i.e., physical objects that are available for
interaction over a network. 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-
based format and a compact format (its Annex C), this specification
defines a compact format to go along SDF's JSON-based 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/. Subscribe at
https://www.ietf.org/mailman/listinfo/asdf/.
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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 27 October 2024.
Copyright Notice
Copyright (c) 2024 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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Example Definition . . . . . . . . . . . . . . . . . . . 4
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Normative References . . . . . . . . . . . . . . . . . . 6
5.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Example in SDF JSON format . . . . . . . . . . . . . 7
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
The Semantic Definition Format (SDF, [I-D.ietf-asdf-sdf]) is a format
for domain experts to use in the creation and maintenance of data and
interaction models that describe Things, i.e., physical objects that
are available for interaction over a network. 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 [RELAXNG] has an XML-based
format and a compact format (its Annex C), this specification defines
a compact format to go along SDF's JSON-based 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.
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 presentation
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.
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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).
2.1. Example Definition
Figure 1 is an SDF-compact representation 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.)
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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
pedaling/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.
Figure 1: Example SDF model in SDF compact form
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 the order does not carry semantics, neither in the
JSON form nor in the compact form.
3. IANA Considerations
This section is to be removed before publishing as an RFC.
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This document does not make any requests of IANA.
4. Security Considerations
The security considerations of [I-D.ietf-asdf-sdf] apply.
Additional security considerations arise as in all alternative
representation forms for a formal description technique. (Security
considerations are given for RELAX-NG compact form in [RELAXNG],
Annex C.7 (Media type registration template for the RELAX NG Compact
Syntax); these actually apply to SDF in general. A more detailed
discussion of the consequences of using dereferenceable identifiers
can be found in the penultimate paragraph of Section 8 (Security
Considerations) of [I-D.ietf-asdf-sdf].)
5. References
5.1. Normative References
[I-D.ietf-asdf-sdf]
Koster, M., Bormann, C., and A. Keränen, "Semantic
Definition Format (SDF) for Data and Interactions of
Things", Work in Progress, Internet-Draft, draft-ietf-
asdf-sdf-18, 28 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-asdf-
sdf-18>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/rfc/rfc8610>.
5.2. 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,
<https://www.iso.org/standard/52348.html>. This
specification is also publicly available at
https://standards.iso.org/ittf/PubliclyAvailableStandards/
c052348_ISO_IEC_19757-2_2008(E).zip
(https://standards.iso.org/ittf/
PubliclyAvailableStandards/
c052348_ISO_IEC_19757-2_2008(E).zip).
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[RFC8792] Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
"Handling Long Lines in Content of Internet-Drafts and
RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
<https://www.rfc-editor.org/rfc/rfc8792>.
[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
This appendix shows the result of automatically converting Figure 1
into the JSON form of SDF. It was produced using the prototype sdfc
tool.
Note that JSON was not designed to enable JSON texts to always fit
into the confines of the RFC format; the presentation here employs
[RFC8792] line wrapping, which is of course not visible in the actual
JSON text for the example presented in Figure 2.
=============== 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."
},
"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."
},
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"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"
]
}
}
}
Figure 2: Example SDF model in JSON text form, line-wrapped
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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