One document matched: draft-ietf-conneg-feature-reg-00.txt
Content Feature Tag Registration Procedure
draft-ietf-conneg-feature-reg-00.txt
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ABSTRACT
Recent Internet applications, such as the World Wide Web, tie
together a great diversity in data formats, client and server
platforms, and communities. This has created a need for content
feature descriptions and negotiation mechanisms in order to identify
and reconcile the form of information to the capabilities and
preferences of the parties involved.
Extensible content feature identification and negotiation mechanisms
require a common vocabulary in order to positively identify content
features. A registration process and authority for content features
is defined with the intent of sharing this vocabulary between
communicating parties. In addition, a URI tree is defined to enable
sharing of content feature definitions without registration.
This document defines a registration procedure which uses the
Internet Assigned Numbers Authority (IANA) as a central registry for
the content feature vocabulary.
TABLE OF CONTENTS
1 Introduction
2 Feature tag definitions
2.1 Feature tag purpose
2.2 Feature tag syntax
3 Feature tag registration
3.1 Registration trees
3.1.1 IETF tree
3.1.2 Global tree
3.1.3 URL tree
3.1.4 Additional registration trees
3.2 Location of registered feature tag list
3.3 IANA procedures for registering feature tags
3.4 Registration template
4 Security considerations
5 Acknowledgments
6 References
7 Authors' addresses
Appendix A: IANA and RFC editor to-do list
1 Introduction
Recent Internet applications, such as the World Wide Web, tie
together a great diversity in data formats, client and server
platforms, and communities. This has created a need for content
feature descriptions and negotiation mechanisms in order to identify
and reconcile the form of information to the capabilities and
preferences of the parties involved.
Extensible content feature identification and negotiation mechanisms
require a common vocabulary in order to positively identify content
features. A registration process and authority for content features
is defined with the intent of sharing this vocabulary between
communicating parties. In addition, a URI tree is defined to enable
sharing of content feature definitions without registration.
This document defines a registration procedure which uses the
Internet Assigned Numbers Authority (IANA) as a central registry for
the content feature vocabulary.
2 Feature tag definitions
2.1 Feature tag purpose
Content feature tags represent individual and simple dimensions of
feature capability. Examples of content features related to media
are:
* the color depth of the screen on which something is to be displayed
* the support of the `floating 5 dimensional tables' feature
* the type of paper available in a printer
* the fonts which are available to the recipient
* the capability to display graphical content
A feature tag identifies a single dimension of characteristic. Feature
tag values should be represented as(and must be representable or
isomorphic to) boolean, enumerated values, or numeric values.
Examples of feature tags are defined in detail elsewhere [4].
Many features are not Boolean and require values to qualify them.
Examples of feature tags with values are:
* the width of a display in pixels represented as an integer value.
* the fonts available to a recipient as an enumerated list.
* the version of a protocol composed of integers "i.j.k", defined as
either a value in an enumerated list or isomorphic to the integer
numeric value ijk.
Complex features should be composed using a number of individual
content feature tags [2]. Composition of complex features is described
elsewhere [2]. Examples of complex features requiring multiple
feature tags are:
* the width and height of a display
* the combination of color depth and resolution a display can support
Features of content already described and registered (such as MIME
types) should not be registered again.
The feature tag namespace is not bound to a particular transport
protocol or capability exchange mechanism. There is no restriction on
the type of content feature which may be identified by a feature tag,
other than the intent of expressing a capability or a preference
regarding a presentation-related feature of content. Feature tags
indicating political or social context are not appropriate.
2.2 Feature tag syntax
A feature tag is a string consisting of one or more of the following
US-ASCII characters: uppercase letters, lowercase letters, digits,
colon (":"), slash ("/"), dot (".") and dash ("-"). Feature tags are
case-insensitive. Dots are understood to potentially imply heirarchy;
a feature can be subtyped by describing it as tree.feature.subfeature
and by indicating this in the feature registration.
A feature tag value is a string consisting of one or more of the
following US-ASCII characters: uppercase letters, lowercase letters,
digits, colon (":"), slash("/"), dot("."), and dash ("-"). Values are
case-insensitive. Feature tag values should be simple atomic values
of either enumerated or numeric form and must be isomorphic with
either enumerated or numeric values. The form of feature tag values
is indicated upon feature registration.
3 Feature tag registration
Feature tags can be registered in several different registration
trees, with different requirements as discussed below. In general, a
feature tag registration proposal is circulated and reviewed in a
fashion appropriate to the tree involved. The feature tag is then
registered if the proposal is accepted. Review of a feature tag
registration in the URI tree is not required.
3.1 Registration trees
The following subsections define registration "trees", distinguished
by the use of faceted names (e.g., names of the form "tree.feature-
name").
3.1.1 IETF tree
The IETF tree is intended for feature tags of general interest to the
Internet Community. Registration in the IETF tree requires approval
by the IESG and publication of the feature tag specification an RFC.
Submissions for feature tag registration in the IETF tree can
originate in any WG of IETF.
Feature tags in the IETF tree normally have names that are not
explicitly faceted, i.e., do not contain period (".", full stop)
characters.
The "owner" of a feature tag in the IETF tree is assumed to be the
IETF itself. Modification or alteration of the specification requires
the same level of processing (e.g. standards track) required for the
initial registration.
3.1.2 Global tree
Tags in the global tree will be distinguished by the leading facet
"g.". That may be followed, at the discretion of the registration, by
either a designation indicative of the feature, (e.g., "g.blinktags")
or by an IANA-approved designation of the producer's name which is
then followed by a designation of the feature (e.g.,
g.bigcompany.obscurefeature).
Registration of a new content feature tag in the global tree is
initiated by the submission of a registration proposal to IANA. The
global tree is intended for feature tags of general interest to the
Internet Community. Unlike registration in the IETF tree,
registration in the global tree does not imply or require approval by
the IESG. A registration may be placed in the global tree by anyone
who has the need to allow for communication on a particular capability
or preference.
If the creator of an Internet service or product introduces a new
content feature to the Internet Community, and if it is meaningful to
identify a content feature tag with it, the feature can be associated
with a feature tag by registration in the global tree.
Registration of a content feature tag does not in itself imply any
form of ownership or control of the underlying feature by the
originator of the registration.
The owner of "global" content feature tag is the person or entity
making the registration, or one to whom responsibility has been
transferred as described below.
While public exposure and review of feature tags to be registered in
the global tree is not required, using the ietf-feature-tags@iana.org
list for review is strongly encouraged to improve the quality of those
specifications.
3.1.3 URI tree
A feature tag may be defined as a URI using the restricted character
set defined above. Feature tags in the URI tree are identified by the
leading facet "u.". The author of the URI is assumed to be
registration authority regarding features defined and described by the
content of the URI. These tags are considered unregistered for the
purpose of this document.
3.1.4 Additional registration trees
From time to time and as required by the community, the IANA may, with
the advice and consent of the IESG, create new top-level registration
trees. These trees may be created for external registration and
management by (for example) well-known permanent bodies, such as
scientific societies for content feature types specific to the
sciences they cover. Establishment of these new trees will be
announced through RFC publication approved by the IESG.
3.2 Location of registered feature tag list
Feature tag registrations will be posted in the anonymous FTP
directory "ftp://ftp.isi.edu/in-notes/iana/assignments/feature- tags/"
and all registered feature tags will be listed in the periodically
issued "Assigned Numbers" RFC [currently STD 2, RFC-1700]. The
feature tag description and other supporting material may also be
published as an Informational RFC by sending it to "rfc-
editor@isi.edu" (please follow the instructions to RFC authors [RFC-
1543]).
3.3 IANA procedures for registering feature tags
The IANA will only register feature tags in the IETF tree in response
to a communication from the IESG stating that a given registration has
been approved.
Global tags will be registered by the IANA automatically and without
any formal review as long as the following minimal conditions are met:
(1) A feature tag must serve as an actual identifier of an area of
content feature or capability.
(2) A feature tag name must be unique, and must conform to the
syntax in section 2.
(3) An openly available description of the feature or capability is
minimally required. The specification of a feature tag must
state whether the choice in the indicated area is a simple yes/no
choice, a numeric value, or a choice among enumerated or multiple
values. If the choice is among multiple values, and a canonical
format for these values is defined, these values must conform to
the syntax in section 2.
(4) Any security considerations given must not be obviously bogus.
(It is neither possible nor necessary for the IANA to conduct a
comprehensive security review of feature tag registrations.
Nevertheless, the IANA has the authority to identify obviously
incompetent material and exclude it.)
3.4 Registration template
To: ietf-feature-tags@iana.org (Feature tags mailing list)
(or directly to iana@iana.org)
Subject: Registration of feature tag XXXX
| Instructions are preceded by `|'. Some fields are optional.
Content feature tag name:
Summary of the content feature indicated by this feature tag:
| Include a short (no longer than 4 lines) description or summary
| Examples:
| `Use of the xyzzy feature is indicated by ...'
| `Support of color display is indicated by ...'
| `Number of colors in a palette which can be defined ...'
Number of possible values associated with this feature tag:
[ ] 1. The feature tag is Boolean and the feature tag has no
associated value. The tag indicates presence (or absence) of
the feature.
[ ] 2. The feature has an associated numeric or enumerated value.
For case 1: describe the nature of the `yes' and `no' alternatives:
For case 2: How is a single alternative result naturally identified?
[ ] 2a. With a name, keyword, label, or tag (e.g. a language tag)
[ ] 2b. With an integer value
[ ] 2c. With a numeric value of a non-integer type (e.g. float)
[ ] 2d. Other (must be isomorphic to 2a, 2b, or 2c.)
(Only for case 2) Detailed description of the feature value meaning,
and of the format (for 2a,2d) and meaning of the feature tag values
for the alternative results:
| If the number of alternative results is small, the description
| could simply enumerate the identifiers of the different results
| and describe their meaning.
|
| If there is a limited useful numeric range of result (2b, 2c),
| indicate the range.
|
| The identifiers of the alternative results could also be
| described by referring to another IANA registry, for example
| the MIME media type registry.
Expected value or behavior in the absence of the feature tag (if
applicable):
The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms:
[optional]
| For applications, also specify the number of the first version
| which will use the tag, if applicable.
Examples of typical use: [optional]
Related standards or documents: [optional]
Considerations particular to use in individual applications,
protocols, services, or negotiation mechanisms: [optional]
Interoperability considerations: [optional]
Security considerations:
Privacy concerns, related to exposure of personal information:
Denial of service concerns related to consequences of specifying
incorrect values:
Other:
Additional information: [optional]
Keywords: [optional]
Related feature tags: [optional]
Related media types or data formats: [optional]
Related HTML markup tags: [optional]
Person & email address to contact for further information:
Intended usage:
| one of COMMON, LIMITED USE or OBSOLETE
Author/Change controller:
Requested IANA publication delay: [optional]
| A delay may only be requested for registration in global or
| local trees, with a maximum of two months.
Other information: [optional]
| Any other information that the author deems interesting may be
| added here.
4 Security considerations
When used, negotiation mechanisms usually reveal some information
about one party to other parties. This may raise privacy concerns,
and may allow a malicious party to make more educated guesses about
the presence of security holes in the other party.
5 Acknowledgments
The details of the registration procedure in this document were
directly adapted from [1]. Much of the text in section 3 was
directly copied from this source.
The idea of creating a vocabulary of areas of content features,
maintained in a central open registry, is due to discussions on
extensible negotiation mechanisms [3] in the IETF HTTP working group.
The authors wish to thank Ted Hardie, Larry Masinter and Graham Klyne
for contributing to discussions about feature tag registration.
6 References
[1] N. Freed, J. Klensin, J. Postel, Multipurpose Internet Mail
Extensions (MIME) Part Four: Registration Procedures. RFC 2048,
BCP 13, Network Working Group, November 1996
[2] G. Klyne, An algebra for describing media feature sets, Internet
Draft: <draft-ietf-conneg-feature-algebra-00.txt> Work in progress
March 1998
[3] Holtman, K., et al, "The Alternates Header Field", Internet-Draft
draft-ietf-http-alternates-01.txt, Work in progress, November 1997.
[4] Masinter, L., et al, "Media Features for Display, Print, and Fax",
Internet-Draft draft-ietf-conneg-media-features-00.txt, Work in
progress , March 1998.
7 Authors' addresses
Koen Holtman
Technische Universiteit Eindhoven
Postbus 513
Kamer HG 6.57
5600 MB Eindhoven (The Netherlands)
Email: koen@win.tue.nl
Andrew H. Mutz
Hewlett-Packard Company
11000 Wolfe Rd. 42UO
Cupertino CA 95014 USA
Fax +1 408 447 4439
Email: andy_mutz@hp.com
Edward Hardie
NASA NIC
hardie@nic.nasa.gov
Appendix A: IANA and RFC editor to-do list
VERY IMPORTANT NOTE: This appendix is intended to communicate
various editorial and procedural tasks the IANA and the RFC
Editor should undertake prior to publication of this document
as an RFC. This appendix should NOT appear in the actual RFC
version of this document!
This document refers to the feature tags mailing list
ietf-feature-tags@iana.org. This list does not exist at the
present time and needs to be created.
The ftp://ftp.isi.edu/in-notes/iana/assignments/feature-tags/"
area does not exist at the present time and needs to be created.
Expires: September 11, 1998
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