HTTP Working Group Koen Holtman, TUE Internet-Draft Andrew Mutz, Hewlett-Packard Expires: January 28, 1998 July 28, 1997 Feature Tag Registration Procedures draft-ietf-http-feature-reg-02.txt STATUS OF THIS MEMO This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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". To learn the current status of any Internet-Draft, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Distribution of this document is unlimited. Please send comments to the HTTP working group at . Discussions of the working group are archived at . General discussions about HTTP and the applications which use HTTP should take place on the mailing list. A HTML version of this document can be found at . 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 various kinds of negotiation mechanisms, which tailor the data which is exchanged, or the exchange process, to the capabilities and preferences of the parties involved. Extensible negotiation mechanisms need a vocabulary to identify various things which can be negotiated on. To promote interoperability, a registration process is needed to ensure that that this vocabulary, which can be shared between negotiation mechanisms, is developed in an orderly, well-specified, and public manner. This document defines registration procedures which use the Internet Assigned Numbers Authority (IANA) as a central registry for this vocabulary, which is the vocabulary of feature tags. TABLE OF CONTENTS 1 Introduction 2 Basic concepts and definitions 2.1 Areas of negotiation and feature tags 2.2 Complexity of negotiation 2.3 The result in an area of negotiation 2.4 Feature tag syntax 3 Feature tag registration 3.1 Registration trees 3.1.1 IETF tree 3.1.2 Global tree 3.1.3 Local or specialized tree 3.1.4 Special `x.' tree 3.1.5 Additional registration trees 3.2 Registration requirements 3.2.1 Functionality requirement 3.2.2 Naming requirements 3.2.3 Specification requirements 3.2.4 Interchange recommendations 3.2.5 Security requirements 3.2.6 Publication requirements 3.3 Registration procedure 3.3.1 Present the feature tag to the community for review 3.3.2 IESG approval 3.3.3 IANA registration 3.3.4 Delayed publication 3.4 Comments on feature tag registrations 3.5 Location of registered feature tag list 3.6 IANA procedures for registering feature tags 3.7 Change control 3.8 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 various kinds of negotiation mechanisms, which tailor the data which is exchanged, or the exchange process itself, to the capabilities and preferences of the parties involved. Extensible negotiation mechanisms need a vocabulary to identify various things which can be negotiated on. To promote interoperability, a registration process is needed to ensure that that this vocabulary, which can be shared between negotiation mechanisms, is developed in an orderly, well-specified, and public manner. This document defines registration procedures which use the Internet Assigned Numbers Authority (IANA) as a central registry for this vocabulary, which is the vocabulary of feature tags. 2 Basic concepts and definitions 2.1 Areas of negotiation and feature tags Something which can be negotiated on is called an `area of negotiation' in this document. Examples of areas of negotiation are: * the MIME media type of the data which is transmitted * the language of the text document which is transmitted * the color depth of the screen on which something is to be displayed * whether the recipient supports the `floating 5 dimensional tables' feature * the fonts which are available to the recipient * whether a Web user prefers speed over graphical detail * whether the recipient is capable of displaying graphical content * whether the user prefers a blue background with purple dots over a green background with pictures of small furry animals, except on Fridays. A feature tag identifies a single area of negotiation. It is expected that the majority of feature tags will identify new areas of negotiation, in which the object of negotiation is to decide on the presence or use of some new feature in a software product. This explains the name `feature tag'. It is recognized that there is continuous growth in the number of areas in which some form of negotiation is desirable. To keep up with this growth, extensible negotiation mechanisms are needed, which refer to the feature tag vocabulary to identify new areas of negotiation, rather than relying on hard-coded knowledge about a few areas. To avoid the duplication of work, and to promote the interoperable naming of areas of negotiation across protocols and applications, the feature tag namespace is not bound to a particular protocol or negotiation mechanism. Also, there is no prior restriction on the areas of negotiation which may be identified by a feature tag, other than that it must be conceivable to negotiate in these areas in the context of some Internet application. 2.2 Complexity of negotiation Negotiation processes can often be complex. Two frequent sources of complexity are: 1. An area of negotiation may be inherently complex. For example, negotiating on the use of a particular media type is inherently more complex than negotiating on the presence of a single feature, because there are more possible outcomes. 2. There may be complex of interdependencies between the choices in different areas of negotiation. For example, if the following versions of a document are available on a Web server: * text/html, English * text/plain, French * audio/x-wav, German then the content negotiation mechanism cannot treat the areas of `MIME media type negotiation' and `language negotiation' as separate. It is recognized that extensible negotiation mechanisms will often differ in the type and amount of complexity they can handle. Thus, though negotiation mechanisms share the feature tag namespace, it will not be the case that every tag is usable in every negotiation mechanism, or that every negotiation mechanism will be able to handle all possible interdependencies. 2.3 The result in an area of negotiation During negotiation, negotiation mechanisms will often need to transmit (canonical representations of) the possible results in various areas of negotiation over the wire. Also, at the end of a negotiation process, the mechanism may need to return (a canonical representation of) the result to the application which invoked it. In many areas of negotiation, there will be a natural, canonical representation of the result. For example, in the area * whether the recipient supports the `floating 5 dimensional tables' feature the canonical representation of the result is a boolean value (yes, the feature is supported, or no, the feature is not supported). In the area * the MIME media type of the data which is transmitted the canonical representation of the result will be a MIME media type identifier like text/html or application/postscript. In some areas of negotiation, the result could be a compound value (e.g. a coordinate in a 3D space). To promote interoperability, the registration entry of a feature tag can include a definition of the canonical representations of the possible results in the corresponding area of negotiation. 2.4 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, the dot (".") and the dash ("-"). Feature tags are case-insensitive. 3 Feature tag registration Registration of a new feature tag starts with the construction of a registration proposal. Registration may occur in several different registration trees, which have different requirements as discussed below. In general, the new registration proposal is circulated and reviewed in a fashion appropriate to the tree involved. The feature tag is then registered if the proposal is acceptable. The following sections describe the requirements and procedures used for each of the different registration trees. 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 as some form of RFC. 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 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 require approval by the IESG. A registration may be placed in the global tree by anyone who has the need to allow for feature negotiation on a particular capability or preference. Typically, if the creator of an Internet service or product introduces something new to the Internet Community, and if it is meaningful to do negotiation on it, the vendor can register a feature tag in the global tree. The owner of "global" tags and associated specifications is the person or entity making the registration, or one to whom responsibility has been transferred as described below. 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 of an area of negotiation, (e.g., "g.blinktags") or by an IANA-approved designation of the producer's name which is then followed by a designation of an area of negotiation (e.g., g.bigcompany.obscurefeature). While public exposure and review of feature tags to be registered in the global tree is not required, using the ietf-feature-tags list for review is strongly encouraged to improve the quality of those specifications. Registrations in the global tree may be submitted directly to the IANA. 3.1.3 Local or specialized tree The local tree is intended for feature tags identifying areas of negotiation which are relevant in a localized, specialized, restricted, or experimental context. The owner of "local" tags and associated specifications is the person or entity making the registration, or one to whom responsibility has been transferred as described below. Tags in the local tree will be distinguished by the leading facet "l.". While public exposure and review of feature tags to be registered in the local tree is not required, using the ietf-feature-tags list for review is strongly encouraged to improve the quality of those specifications. Registrations in the local tree may be submitted directly to the IANA. 3.1.4 Special `x.' tree Feature tags with "x." as the first facet are reserved for use in experimental contexts. These tags are unregistered, experimental, and should be used only with the active agreement of the parties exchanging them. However, with the simplified registration procedures described above for vendor and personal trees, it should rarely, if ever, be necessary to use unregistered experimental tags, and as such use of these tags is discouraged. 3.1.5 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. It is explicitly assumed that these trees may be created for external registration and management by well-known permanent bodies, such as scientific societies for media types specific to the sciences they cover. In general, the quality of review of specifications for one of these additional registration trees is expected to be equivalent to that which IETF would give to registrations in its own tree. Establishment of these new trees will be announced through RFC publication approved by the IESG. 3.2 Registration requirements Feature tag registration proposals are all expected to conform to various requirements laid out in the following sections. Note that requirement specifics sometimes vary depending on the registration tree, again as detailed in the following sections. 3.2.1 Functionality requirement A feature tag must function as an actual identifier of an area of negotiation, and it must be conceivable to negotiate in this area in the context of some Internet application. This requirement applies regardless of the registration tree involved. 3.2.2 Naming requirements All feature tag names must be unique, and must conform to the syntax in section 2.4. This requirement applies regardless of the registration tree involved. The IANA may reject tag names which are obviously bogus or misleading. Note however that other than in the IETF tree, the acceptance of a feature tag does not imply certification that the tag is adequately named. 3.2.3 Specification requirements If a feature tag is registered in the IETF tree, a precise and openly available specification of the indicated area of negotiation is required, and must at a minimum be referenced by, if it isn't actually included in, the feature tag registration proposal itself. For the global and local trees, an openly available description of the area is minimally required. Regardless of the tree, the specification of a feature tag must state whether the choice in the indicated area is a simple yes/no choice, or if it is a choice for a single value among multiple values. If the choice in the indicated area is among multiple values, and it is possible to define canonical representations for the different possible result values, and the tag is registered in the IETF tree, a precise and openly available specification of the canonical format, and the exact meaning of the values is required, and must at a minimum be referenced by, if it isn't actually included in, the feature tag registration proposal itself. For any canonical format which is defined, it must be possible to map this format onto octet strings. If the registration is motivated by the creation of a new feature in a product, it is specifically permitted to name the product involved, and the product version number for which the feature was or will be first implemented. The registration of feature tags referencing patented technology is specifically permitted. However the restrictions set forth in RFC 1602 on the use of patented technology in standards-track protocols must be respected when the specification of a feature tag is part of a standards-track protocol. 3.2.4 Interchange recommendations Feature tags should, whenever possible, interoperate across as many systems, applications, and negotiation mechanisms as possible. However, some feature tags will by nature be bound to specific systems, and feature tag may indicate areas of negotiation in which the choice is made among types of values which can only be handled by highly specialized negotiation mechanisms. Universal interoperability of feature tags is not required, but known interoperability issues should be identified whenever possible. Publication of a feature tag does not require an exhaustive review of interoperability, and the interoperability considerations section is subject to continuing evaluation. These recommendations apply regardless of the registration tree involved. 3.2.5 Security requirements An analysis of security issues is required for all feature tags registered in the IETF tree. (This is in accordance with the basic requirements for all IETF protocols.) A similar analysis for feature tags registered in the global or local trees is encouraged but not required. All descriptions of security issues must be as accurate as possible regardless of registration tree. In particular, a statement that there are "no security issues associated with the indicated feature tag" must not be confused with "the security issues associates with this feature tag have not been assessed". There is absolutely no requirement that systems which negotiate using the feature tags registered in any tree be secure or completely free from risks. Nevertheless, all known security risks must be identified in the registration of a feature tag, again regardless of registration tree. The security considerations section of all registrations is subject to continuing evaluation and modification, and in particular may be extended by use of the "comments on feature tags" mechanism described in subsequent sections. 3.2.6 Publication requirements Proposals for feature tags registered in the IETF tree must be published as RFCs. RFC publication of global and local feature tag proposals is not required. In all cases the IANA will retain copies of all feature tag proposals and "publish" them as part of the feature tag registration tree itself. Other than in the IETF tree, the registration of a feature tag does not imply endorsement, approval, or recommendation by the IANA or the IETF or even certification that the specification is adequate. It is neither possible nor necessary for the IANA to conduct a comprehensive review of feature tag registrations. Nevertheless, the IANA has the authority to identify obviously incompetent material and exclude it. 3.3 Registration procedure The following procedure has been implemented by the IANA for review and approval of new feature tags. This is not a formal standards process, but rather an administrative procedure intended to allow community comment and sanity checking without excessive time delay. For registration in the IETF tree, the normal IETF processes should be followed, treating posting of an internet-draft and announcement on the ietf-types list (as described in the next subsection) as a first step. For registrations in the global or local trees, the initial review step described below may be omitted and the tag registered directly by submitting the template and an explanation to the IANA (at iana@isi.edu). However, authors of global or local feature tag specifications are encouraged to seek community review and comment whenever that is feasible. 3.3.1 Present the feature tag to the community for review Send a proposed feature tag registration to the "ietf-feature-tags@iana.org" mailing list for a two week review period. This mailing list has been established for the purpose of reviewing proposed feature tags. Proposed feature tags are not formally registered and must not be used; the "x." prefix can be used until registration is complete. The intent of the public posting is to solicit comments and feedback on the choice of tag name, the clarity of the tag specification, and a review of any interoperability or security considerations. The submitter may submit a revised registration proposal, or withdraw the registration proposal completely, at any time. 3.3.2 IESG approval Feature tags registered in the IETF tree must be submitted to the IESG for approval. 3.3.3 IANA registration Provided that the proposed tag meets the requirements for feature tags and has obtained whatever approval is necessary, the author may submit the registration request to the IANA, which will register the feature tag and make the feature tag registration available to the community. 3.3.4 Delayed publication By default, feature tag registration proposals are published by the IANA immediately after registration of the tag. In some situations, a vendor may not wish that a specification of a tag for a planned new feature is published before the date at which the software implementing this feature is released to the Internet Community. Therefore, when submitting a feature tag registration proposal for a planned feature, a vendor may request a publication delay of up to two months after registration of the tag by the IANA. After registration, IANA will delay its publication of the registration proposal for at least the duration of the requested period. Immediately after receiving a notification of registration from the IANA, the vendor may release software which recognizes the tag to the Internet Community, and make public the tag specification though his own channels. 3.4 Comments on feature tag registrations Comments on registered feature tags may be submitted by members of the community to the IANA. These comments will be passed on to the "owner" of the feature tag if possible. Submitters of comments may request that their comment be attached to the feature tag registration itself, and if the IANA approves of this the comment will be made accessible in conjunction with the tag registration itself. 3.5 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]). 3.6 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 and local 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 function as an actual identifier of an area of negotiation. (2) All feature tag names must be unique, and must conform to the syntax in section 2.4. (3) An openly available description of the area of negotiation is minimally required. The specification of a feature tag must state whether the choice in the indicated area is a simple yes/no choice, or if it is a choice among multiple values. If the choice is among multiple values, and a canonical format for these values is defined, it must be possible to map this format onto octet strings. (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.) 3.7 Change control Once a feature tag has been published by the IANA, the owner may request a change to its definition. The descriptions of the different registration trees above designate the "owners" of each type of registration. The change request follows the following procedure: (1) Publish the revised template on the ietf-feature-tags list. (2) Leave at least two weeks for comments. (3) Publish using the IANA after formal review if required. Changes should be requested only when there are serious omissions or errors in the published specification. When review is required, a change request may be denied if it renders a use of tags that was valid under the previous definition invalid under the new definition. The owner of a feature tag may pass responsibility for the feature tag to another person or agency by informing the IANA and the ietf-feature-tags list; this can be done without discussion or review. The IESG may reassign responsibility for a feature tag. The most common case of this will be to enable changes to be made to tags where the author of the registration has died, moved out of contact or is otherwise unable to make changes that are important to the community. Feature tag registrations may not be deleted; feature tags which are no longer believed appropriate for use can be declared OBSOLETE by a change to their "intended use" field; such feature tags will be clearly marked in the lists published by the IANA. 3.8 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. Feature tag name: Summary of the area of negotiation indicated by this feature tag: | Include a short (no longer than 4 lines) description or summary | Examples: | `Negotiation on whether to use the xyzzy feature of ...' | `Negotiation on the MIME media type of the data which | is transmitted for ...' | `Negotiation on whether to use colors in displaying ...' | `Negotiation on the number of colors to use in displaying ...' Number of alternative results in this area of negotiation: [ ] 1. Two alternatives, which can be labeled with `yes' and `no' [ ] 2. More than two alternatives, or two alternatives with no natural `yes/no' labeling For case 1: nature of the `yes' and `no' alternatives: [ ] 1a. A particular feature is used/invoked/enabled, or not [ ] 1b. Other 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 [ ] 2e. There is no simple way to identify a single result (Only for case 1a) Description of the feature which is used, invoked, or enabled if the result is `yes': | Descriptions may also reference outside material. (Only for case 1b) Description of the effect of the 'yes' result: (Only for case 1b) Description of the effect of the 'no' result: (Only for case 2) Detailed description of the area of negotiation, and (in cases 2a-2d) of the format and meaning of the identifiers 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. | | The identifiers of the alternative results could also be | described by referring to another IANA registry, for example | the MIME media type registry. Default negotiation result (if applicable to the intended application domain): The feature tag is intended for use in the 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: 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 negotiation, which is maintained in a central open registry, is due to discussions on extensible negotiation mechanisms in the IETF HTTP working group. The authors wish to thank 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 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 1501 Page Mill Road 3U-3 Palo Alto CA 94304, USA Fax +1 415 857 4691 Email: mutz@hpl.hp.com 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: January 28, 1998