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An sdfType for Links
draft-bormann-asdf-sdftype-link-00

Document Type Active Internet-Draft (individual)
Author Carsten Bormann
Last updated 2022-12-01
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draft-bormann-asdf-sdftype-link-00
ASDF WG                                                       C. Bormann
Internet-Draft                                    Universit├Ąt Bremen TZI
Intended status: Standards Track                         1 December 2022
Expires: 4 June 2023

                          An sdfType for Links
                   draft-bormann-asdf-sdftype-link-00

Abstract

   This document defines and registers an sdfType "link" for the
   Semantic Definition Format (SDF) for Data and Interactions of Things
   (draft-ietf-asdf-sdf-12.txt).

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-sdftype-link/.

   Discussion of this document takes place on the A Semantic Definition
   Format for Data and Interactions of Things 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/.

   Source for this draft and an issue tracker can be found at
   https://github.com/cabo/sdftype-link.

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 4 June 2023.

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Copyright Notice

   Copyright (c) 2022 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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions and Definitions . . . . . . . . . . . . . . .   3
   2.  The sdfType "link"  . . . . . . . . . . . . . . . . . . . . .   3
   3.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The Semantic Definition Format for Data and Interactions of Things
   (SDF, [I-D.ietf-asdf-sdf]) is a format for domain experts to use in
   the creation and maintenance of data and interaction models in the
   Internet of Things.

   A common data type that occurs in the modeling of IoT devices is the
   _link_. [RFC8288] defines the concept of Web Linking, which
   complements the target URI that any link will contain, with
   additional parameters, such as the "link relation type" that explains
   the relationship expressed by the link, as well as "target
   attributes" that provide additional information about the target of
   the link (without a need to "dereference", i.e., follow, the link).

   This document defines and registers an sdfType "link" for the
   Semantic Definition Format.  This type models an abstract
   "serialization" [RFC8288] of a link, in a way that is compatible with
   the way SDF maps information models to its data modeling language.

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1.1.  Conventions and Definitions

   The definitions of [RFC6690], [RFC8288], and [I-D.ietf-asdf-sdf]
   apply.

2.  The sdfType "link"

   The sdfType "link" is intended to be used with the SDF "type" of
   "object".  The members of that object are strings that are named the
   same as the link parameter (attribute) names.  The special parameter
   name "href" is used to express the link target.  (Parameter names
   specific to the Constrained RESTful Environment (CoRE) are also
   discussed in [I-D.bormann-core-target-attr].)

   An example for the instance of a link is provided in Section 5 of
   [RFC6690]:

      </sensors/temp>;rt="temperature-c";if="sensor",

   An sdfProperty that is used to describe an SDF affordance that is
   intended to hold a link like this (without getting specific on the
   actual link to the link target) could look like:

   {
    "sdfProperty": {
     "temp-c-link": {
      "type": "object",
      "sdfType": "link",
      "properties": {
        "href": { "type": "string"},
        "rt": { "type": "string", "const": "temperature-c"},
        "if": { "type": "string", "const": "sensor"}
      }
     }
    }
   }

3.  Discussion

   Links play an important role in SDF modeling both during definition
   time (for adding information to a model, as e.g., in sdfRef) and
   during run time (for making links to instances into a subject of data
   and interaction modeling).  The present document is an early attempt
   at addressing the run-time usage of links, in particular links that
   fit the Web Linking [RFC8288] abstractions.  A related draft
   [I-D.laari-asdf-relations] addresses definition-time links, but does
   seem to touch modeling run-time use of links as well (e.g., by
   discussing "writable" link relations).

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   Not all links used in ecosystems are based on URIs.  E.g., OMA has
   "object links", which are pairs of numbers (object/instance).  These
   ecosystem links may have some structure that should be modeled in the
   SDF model (e.g., where the object id part of a link always has to
   have a specific value).  This structure can be mapped into URI
   strings using some convention, e.g., an OMA object link could be oma-
   object:3303:0 (where oma-object is placeholder for a URI scheme to be
   defined).  However, burying structural components of the ecosystem-
   specific link in a string syntax makes it hard to access and control
   those components from the model.

   Examples are needed to show how the OCF collection pattern is
   addressed by the current specification.

4.  Security Considerations

   The security considerations of [RFC8288] apply in a general way,
   although modeling a link as a datatype does not incur all of the
   security considerations that will apply to actually interchanging
   these links.

   (TODO)

5.  IANA Considerations

   TODO: This document registers the sdfType "link" in the SDF sdfType
   registry (which is to be defined in the SDF specification).

6.  References

6.1.  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-12, 30 June
              2022, <https://www.ietf.org/archive/id/draft-ietf-asdf-
              sdf-12.txt>.

   [RFC8288]  Nottingham, M., "Web Linking", RFC 8288,
              DOI 10.17487/RFC8288, October 2017,
              <https://www.rfc-editor.org/info/rfc8288>.

6.2.  Informative References

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   [I-D.bormann-core-target-attr]
              Bormann, C., "CoRE Target Attribute Registry", Work in
              Progress, Internet-Draft, draft-bormann-core-target-attr-
              01, 6 November 2022, <https://www.ietf.org/archive/id/
              draft-bormann-core-target-attr-01.txt>.

   [I-D.laari-asdf-relations]
              Laari, P., "Extended relation information for Semantic
              Definition Format (SDF)", Work in Progress, Internet-
              Draft, draft-laari-asdf-relations-00, 3 June 2022,
              <https://www.ietf.org/archive/id/draft-laari-asdf-
              relations-00.txt>.

   [RFC6690]  Shelby, Z., "Constrained RESTful Environments (CoRE) Link
              Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
              <https://www.rfc-editor.org/info/rfc6690>.

Acknowledgments

   Discussions in the OneDM liaison organization shaped this proposal.

Author's Address

   Carsten Bormann
   Universit├Ąt Bremen TZI
   Postfach 330440
   D-28359 Bremen
   Germany
   Phone: +49-421-218-63921
   Email: cabo@tzi.org

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