v: 3
title: > CoRE Target Attributes Registry abbrev: CoRE Target Attributes Registry docname: draft-ietf-core-target-attr-latest
updates: 9176
keyword: Internet-Draft cat: info stream: IETF wg: CoRE Working group
venue: mail: "[email protected]" github: core-wg/core-target-attr
pi: [toc, sortrefs, symrefs, compact, comments]
name: Carsten Bormann
org: Universität Bremen TZI
street: Postfach 330440
city: Bremen
code: D-28359
country: Germany
phone: +49-421-218-63921
email: [email protected]
contributor:
- name: Jaime Jiménez organization: Ericsson email: [email protected] contribution: Jaime provided the list of initial registrations.
normative: RFC8288: linking BCP26: -: ianacons =: RFC8126 STD80: -: ascii =: RFC20
informative: RFC6690: link-format RFC7252: coap RFC7641: obs RFC8075: http-proxy RFC8613: oscore RFC5988: linking-old RFC9176: rd
--- abstract
The Constrained RESTful Environments (CoRE) specifications apply Web technologies to constrained environments. One important such technology is Web Linking (RFC 8288), which CoRE specifications use as the basis for a number of discovery protocols, such as the Link Format (RFC 6690) in CoAP's Resource Discovery Protocol (Section 7.2 of RFC7252) and the Resource Directory (RD, RFC 9176).
Web Links can have target attributes, the names of which are not generally coordinated by the Web Linking specification (Section 2.2 of RFC 8288). This document introduces an IANA registry for coordinating names of target attributes when used in CoRE. It updates the RD Parameters IANA Registry created by RFC 9176 to coordinate with this registry.
--- middle
The Constrained RESTful Environments (CoRE) specifications apply Web technologies to constrained environments. One important such technology is Web Linking {{-linking}}, which CoRE specifications use as the basis for a number of discovery protocols, such as the Link Format {{-link-format}} in CoAP's Resource Discovery Protocol ({{Section 7.2 of -coap}}) and the Resource Directory {{-rd}}.
Web Links can have target attributes. The original Web Linking specification ({{Section 3 of -linking-old}}) did not attempt to coordinate names of target attributes except for providing common target attributes for use in the Link HTTP header. The current revision of that specification clarifies ({{Section 2.2 of -linking}}):
{:quote}
This specification does not attempt to coordinate the name of target attributes, their cardinality, or use. Those creating and maintaining serialisations SHOULD coordinate their target attributes to avoid conflicts in semantics or syntax and MAY define their own registries of target attributes.
This document introduces an IANA registry for coordinating names of target attributes when used in CoRE, with specific instructions for the Designated Expert for this registry ({{de-instructions}}). It updates the RD Parameters IANA Registry created by {{-rd}} to coordinate with this registry.
With a registry now available, registration of target attributes is strongly encouraged. The incentive is that an unregistered attribute name might be registered with a different meaning at any time.
{::boilerplate bcp14-tagged}
This specification creates a new Target Attributes registry in the "Constrained RESTful Environments (CoRE) Parameters" registry group {{!IANA.core-parameters}}, with the policy "Expert Review" ({{Section 4.5 of -ianacons}}).
The expert is requested to guide the registrant towards reasonably short target attribute names where the shortness will help conserve resources in constrained systems, but also to be frugal in the allocation of very short names, keeping them in reserve for applications that are likely to enjoy wide use and can make good use of their shortness.
The expert is also instructed to direct the registrant to provide a specification ({{Section 4.6 of -ianacons}}), but can make exceptions, for instance when a specification is not available at the time of registration but is likely forthcoming.
Any questions or issues that might interest a wider audience might be raised by the expert on the [email protected] mailing list for a time-limited discussion. This might include security considerations, or opportunities for orchestration, e.g., when different names with similar intent are being or could be registered.
If the expert becomes aware of target attributes that are deployed and in use, they may also initiate a registration on their own if they deem such a registration can avert potential future collisions.
Each entry in the registry must include:
{:vspace}
Attribute Name:
: a lower case ASCII {{-ascii}} string that starts with a letter and can
contain digits and hyphen-minus characters afterward
([a-z][-a-z0-9]*).
(Note that {{-linking}} requires target attribute names to be
interpreted in a case-insensitive way; the restriction to lower case
here ensures that they are registered in a predictable form).
Brief description: : a brief description
Change Controller: : see {{Section 2.3 of -ianacons}}
Reference: : a reference document that provides a description of the target attribute, including the semantics for when the target attribute appears more than once in a link.
Initial entries in this registry are listed in {{pre-reg}}.
| Attribute Name | Brief description | Change Controller | Reference | | href | reserved (not useful as target attribute name) | IETF | {{RFC6690}} | | anchor | reserved (not useful as target attribute name) | IETF | {{RFC6690}} | | rel | reserved (not useful as target attribute name) | IETF | {{RFC6690}} | | rev | reserved (not useful as target attribute name) | IETF | {{RFC6690}} | | hreflang | (Web Linking) | IETF | {{-linking}} | | media | (Web Linking) | IETF | {{-linking}} | | title | (Web Linking) | IETF | {{-linking}} | | type | (Web Linking) | IETF | {{-linking}} | | rt | resource type | IETF | {{Section 3.1 of RFC6690}} | | if | interface description | IETF | {{Section 3.2 of RFC6690}} | | sz | maximum size estimate | IETF | {{Section 3.3 of RFC6690}} | | ct | Content-Format hint | IETF | {{Section 7.2.1 of RFC7252}} | | obs | observable resource | IETF | {{Section 6 of RFC7641}} | | hct | HTTP-CoAP URI mapping template | IETF | {{Section 5.5 of RFC8075}} | | osc | hint: resource only accessible using OSCORE | IETF | {{Section 9 of RFC8613}} | | ep | Endpoint Name (with rt="core.rd-ep") | IETF | {{Section 9.3 of RFC9176}} | | d | Sector (with rt="core.rd-ep") | IETF | {{Section 9.3 of RFC9176}} | | base | Registration Base URI (with rt="core.rd-ep") | IETF | {{Section 9.3 of RFC9176}} | | et | Endpoint Type (with rt="core.rd-ep") | IETF | {{Section 9.3 of RFC9176}} | {: #pre-reg title="Initial Entries in the Target Attributes Registry"}
A number of names are reserved as they are used for parameters in links other than target attributes. A further set of target attributes is predefined in {{-linking}} and is imported into this registry.
{{Section 9.3 of RFC9176}} created the "RD Parameters" IANA registry. This document requests IANA to add the following note to that registry:
Note: In accordance with [this document], all entries with the "A" flag set, including new ones, MUST also be registered in the "Target Attributes" registry {{!IANA.core-parameters}}.
The security considerations of {{-linking}} apply, as do those of the discovery specifications {{-link-format}}, {{-coap}}, and {{-rd}}.
--- back
{: numbered="no"}
The CoRE WG had been discussing setting up a registry for target attributes since the final touches were made on {{-link-format}}. The update of the Web Linking specification to {{-linking}} provided the formal setting, but it took until {{{Jaime Jiménez}}} provided the set of initial registrations to generate a first version of this specification. The current version addresses additional input and working group last call comments by {{{Esko Dijk}}}, {{{Marco Tiloca}}}, {{{Thomas Fossati}}}, and {{{Mohamed Boucadair}}}, as well as area director review comments from {{{Rob Wilton}}}.