





Network Working Group                                          T. Hansen
Request for Comments: 4395                             AT&T Laboratories
Obsoletes: 2717, 2718                                          T. Hardie
BCP: 115                                                  Qualcomm, Inc.
Category: Best Current Practice                              L. Masinter
                                                           Adobe Systems
                                                           February 2006


       Guidelines and Registration Procedures for New URI Schemes

Status of This Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document provides guidelines and recommendations for the
   definition of Uniform Resource Identifier (URI) schemes.  It also
   updates the process and IANA registry for URI schemes.  It obsoletes
   both RFC 2717 and RFC 2718.
























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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Guidelines for Permanent URI Scheme Definitions  . . . . . . .  4
     2.1.  Demonstratable, New, Long-Lived Utility  . . . . . . . . .  4
     2.2.  Syntactic Compatibility  . . . . . . . . . . . . . . . . .  5
     2.3.  Well-Defined . . . . . . . . . . . . . . . . . . . . . . .  5
     2.4.  Definition of Operations . . . . . . . . . . . . . . . . .  6
     2.5.  Context of Use . . . . . . . . . . . . . . . . . . . . . .  6
     2.6.  Internationalization and Character Encoding  . . . . . . .  7
     2.7.  Clear Security Considerations  . . . . . . . . . . . . . .  7
     2.8.  Scheme Name Considerations . . . . . . . . . . . . . . . .  7
   3.  Guidelines for Provisional URI Scheme Registration . . . . . .  8
   4.  Guidelines for Historical URI Scheme Registration  . . . . . .  8
   5.  URI Scheme Registration Procedure  . . . . . . . . . . . . . .  9
     5.1.  General  . . . . . . . . . . . . . . . . . . . . . . . . .  9
     5.2.  Registration Procedures  . . . . . . . . . . . . . . . . .  9
     5.3.  Change Control . . . . . . . . . . . . . . . . . . . . . . 10
     5.4.  URI Scheme Registration Template . . . . . . . . . . . . . 11
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 13


























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1.  Introduction

   The Uniform Resource Identifier (URI) protocol element and generic
   syntax is defined by RFC 3986 [5].  Each URI begins with a scheme
   name, as defined by Section 3.1 of RFC 3986, that refers to a
   specification for identifiers within that scheme.  The URI syntax
   provides a federated and extensible naming system, where each
   scheme's specification may further restrict the syntax and semantics
   of identifiers using that scheme.  This document provides guidelines
   for the definition of new URI schemes, for consideration by those who
   are defining, registering, or evaluating those definitions, as well
   as a process and mechanism for registering URI schemes within the
   IANA URI scheme registry.  The registry has two parts: 'provisional'
   and 'permanent', with different requirements.  Guidelines and
   requirements for both parts are given.

   This document obsoletes both RFCs 2717 [7] and 2718 [8].  RFCs 2717
   and 2718 drew a distinction between 'locators' (identifiers used for
   accessing resources available on the Internet) and 'names'
   (identifiers used for naming possibly abstract resources, independent
   of any mechanism for accessing them).  The intent was to use the
   designation "URL" (Uniform Resource Locator) for those identifiers
   that were locators and "URN" (Uniform Resource Name) for those
   identifiers that were names.  In practice, the line between 'locator'
   and 'name' has been difficult to draw: locators can be used as names,
   and names can be used as locators.

   As a result, recent documents have used the term "URI" for all
   resource identifiers, avoiding the term "URL" and reserving the term
   "URN" explicitly for those URIs using the "urn" scheme name (RFC 2141
   [2]).  URN "namespaces" (RFC 3406 [9]) are specific to the "urn"
   scheme and not covered explicitly by this document.

   RFC 2717 defined a set of registration trees in which URI schemes
   could be registered, one of which was called the IETF Tree, to be
   managed by IANA.  RFC 2717 proposed that additional registration
   trees might be approved by the IESG.  However, no such registration
   trees have been approved.

   This document eliminates RFC 2717's distinction between different
   'trees' for URI schemes; instead there is a single namespace for
   registered values.  Within that namespace, there are values that are
   approved as meeting a set of criteria for URI schemes.  Other scheme
   names may also be registered provisionally, without necessarily
   meeting those criteria.  The intent of the registry is to:






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   o  provide a central point of discovery for established URI scheme
      names, and easy location of their defining documents;
   o  discourage use of the same URI scheme name for different purposes;
   o  help those proposing new URI scheme names to discern established
      trends and conventions, and avoid names that might be confused
      with existing ones;
   o  encourage registration by setting a low barrier for provisional
      registrations.

   RFC 3987 [6] introduced a new protocol element, the Internationalized
   Resource Identifier (IRI), and defined a mapping between URIs and
   IRIs.  There is no separate registry or registration process for
   IRIs.  Those who wish to describe resource identifiers that are
   useful as IRIs should define the corresponding URI syntax, and note
   that the IRI usage follows the rules and transformations defined in
   RFC 3987.

   Within this document, the key words MUST, MAY, SHOULD, REQUIRED,
   RECOMMENDED, and so forth are used within the general meanings
   established in RFC 2119 [1], within the context that they are
   requirements on future registration documents.

2.  Guidelines for Permanent URI Scheme Definitions

   This section gives considerations for new URI schemes.  Meeting these
   guidelines is REQUIRED for permanent URI scheme registration.
   Meeting these guidelines is also RECOMMENDED for provisional
   registration, as described in Section 3.

2.1.  Demonstratable, New, Long-Lived Utility

   The use and deployment of new URI schemes in the Internet
   infrastructure is costly; some parts of URI processing may be
   scheme-dependent, and deployed software already processes URIs of
   well-known schemes.  Introducing a new URI scheme may require
   additional software, not only for client software and user agents but
   also in additional parts of the network infrastructure (gateways,
   proxies, caches) [11].  URI schemes constitute a single, global
   namespace; it is desirable to avoid contention over use of short,
   mnemonic scheme names.  For these reasons, the unbounded registration
   of new schemes is harmful.  New URI schemes SHOULD have clear utility
   to the broad Internet community, beyond that available with already
   registered URI schemes.








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2.2.  Syntactic Compatibility

   RFC 3986 [5] defines the generic syntax for all URI schemes, along
   with the syntax of common URI components that are used by many URI
   schemes to define hierarchical identifiers.  All URI scheme
   specifications MUST define their own syntax such that all strings
   matching their scheme-specific syntax will also match the
   <absolute-URI> grammar described in Section 4.3 of RFC 3986.

   New URI schemes SHOULD reuse the common URI components of RFC 3986
   for the definition of hierarchical naming schemes.  However, if there
   is a strong reason for a URI scheme not to use the hierarchical
   syntax, then the new scheme definition SHOULD follow the syntax of
   previously registered schemes.

   URI schemes that are not intended for use with relative URIs SHOULD
   avoid use of the forward slash "/" character, which is used for
   hierarchical delimiters, and the complete path segments "." and ".."
   (dot-segments).

   Avoid improper use of "//".  The use of double slashes in the first
   part of a URI is not an artistic indicator that what follows is a
   URI: Double slashes are used ONLY when the syntax of the URI's
   <scheme-specific-part> contains a hierarchical structure as described
   in RFC 3986.  In URIs from such schemes, the use of double slashes
   indicates that what follows is the top hierarchical element for a
   naming authority.  (See Section 3.2 of RFC 3986 for more details.)
   URI schemes that do not contain a conformant hierarchical structure
   in their <scheme-specific-part> SHOULD NOT use double slashes
   following the "<scheme>:" string.

   New URI schemes SHOULD clearly define the role of RFC 3986 [5]
   reserved characters in URIs of the scheme being defined.  The syntax
   of the new scheme should be clear about which of the "reserved" set
   of characters (as defined in RFC 3986) are used as delimiters within
   the URIs of the new scheme, and when those characters must be
   escaped, versus when they may be used without escaping.

2.3.  Well-Defined

   While URIs may or may not be useful as locators in practice, a URI
   scheme definition itself MUST be clear as to how it is expected to
   function.  Schemes that are not intended to be used as locators
   SHOULD describe how the resource identified can be determined or
   accessed by software that obtains a URI of that scheme.






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   For schemes that function as locators, it is important that the
   mechanism of resource location be clearly defined.  This might mean
   different things depending on the nature of the URI scheme.

   In many cases, new URI schemes are defined as ways to translate
   between other namespaces or protocols and the general framework of
   URIs.  For example, the "ftp" URI scheme translates into the FTP
   protocol, while the "mid" URI scheme translates into a Message-ID
   identifier of an email message.  For such schemes, the description of
   the mapping must be complete, and in sufficient detail so that the
   mapping in both directions is clear: how to map from a URI into an
   identifier or set of protocol actions or name in the target
   namespace, and how legal values in the base namespace, or legal
   protocol interactions, might be represented in a valid URI.  In
   particular, the mapping should describe the mechanisms for encoding
   binary or character strings within valid character sequences in a URI
   (See Section 2.6 for guidelines).  If not all legal values or
   protocol interactions of the base standard can be represented using
   the URI scheme, the definition should be clear about which subset are
   allowed, and why.

2.4.  Definition of Operations

   As part of the definition of how a URI identifies a resource, a URI
   scheme definition SHOULD define the applicable set of operations that
   may be performed on a resource using the URI as its identifier.  A
   model for this is HTTP; an HTTP resource can be operated on by GET,
   POST, PUT, and a number of other operations available through the
   HTTP protocol.  The URI scheme definition should describe all
   well-defined operations on the URI identifier, and what they are
   supposed to do.

   Some URI schemes don't fit into the "information access" paradigm of
   URIs.  For example, "telnet" provides location information for
   initiating a bi-directional data stream to a remote host; the only
   operation defined is to initiate the connection.  In any case, the
   operations appropriate for a URI scheme should be documented.

   Note: It is perfectly valid to say that "no operation apart from GET
   is defined for this URI".  It is also valid to say that "there's only
   one operation defined for this URI, and it's not very GET-like".  The
   important point is that what is defined on this scheme is described.

2.5.  Context of Use

   In general, URIs are used within a broad range of protocols and
   applications.  Most commonly, URIs are used as references to
   resources within directories or hypertext documents, as hyperlinks to



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   other resources.  In some cases, a URI scheme is intended for use
   within a different, specific set of protocols or applications.  If
   so, the scheme definition SHOULD describe the intended use and
   include references to documentation that define the applications
   and/or protocols cited.

2.6.  Internationalization and Character Encoding

   When describing URI schemes in which (some of) the elements of the
   URI are actually representations of human-readable text, care should
   be taken not to introduce unnecessary variety in the ways in which
   characters are encoded into octets and then into URI characters; see
   RFC 3987 [6] and Section 2.5 of RFC 3986 [5] for guidelines.  If URIs
   of a scheme contain any text fields, the scheme definition MUST
   describe the ways in which characters are encoded, and any
   compatibility issues with IRIs of the scheme.

2.7.  Clear Security Considerations

   Definitions of URI schemes MUST be accompanied by a clear analysis of
   the security implications for systems that use the URI scheme; this
   follows the practice of Security Consideration sections within IANA
   registrations [3].

   In particular, Section 7 of RFC 3986 [5] describes general security
   considerations for URI schemes.  The definition of an individual URI
   scheme should note which of these apply to the specified scheme.

2.8.  Scheme Name Considerations

   Section 3.1 of RFC 3986 defines the syntax of a URI scheme name.  New
   scheme registrations MUST comply.  Note that although scheme names
   are case insensitive, scheme names MUST be registered using lowercase
   letters.

   URI scheme names should be short, but also sufficiently descriptive
   and distinguished to avoid problems.

   Avoid names or other symbols that might cause problems with rights to
   use the name in IETF specifications and Internet protocols.  For
   example, be careful with trademark and service mark names.  (See
   Section 7.4 of RFC 3978 [4].)

   Avoid using names that are either very general purpose or associated
   in the community with some other application or protocol.  Avoid
   scheme names that are overly general or grandiose in scope (e.g.,
   that allude to their "universal" or "standard" nature when the
   described namespace is not.)



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   Organizations that desire a private name space for URI scheme names
   are encouraged to use a prefix based on their domain name, expressed
   in reverse order.  For example, a URI scheme name of com-example-info
   might be registered by the vendor that owns the example.com domain
   name.

3.  Guidelines for Provisional URI Scheme Registration

   While the guidelines in Section 2 are REQUIRED for permanent
   registration, they are RECOMMENDED for provisional registration.  For
   a provisional registration, the following are REQUIRED:

   o  The scheme name meets the syntactic requirements of Section 2.8.
   o  There is not already an entry with the same URI scheme name.  (In
      the unfortunate case that there are multiple, different uses of
      the same scheme name, the IESG may approve a request to modify an
      existing entry to note the separate use.)
   o  Contact information identifying the person supplying the
      registration is included.  Previously unregistered URI schemes
      discovered in use may be registered by third parties on behalf of
      those who created the URI scheme; in this case, both the
      registering party and the scheme creator SHOULD be identified.
   o  If no permanent, citable specification for the URI scheme
      definition is included, credible reasons for not providing it
      should be given.
   o  A valid Security Considerations section, as required by Section 6
      of [3].
   o  If the scheme definition does not meet the guidelines laid out in
      Section 2, the differences and reasons SHOULD be noted.

4.  Guidelines for Historical URI Scheme Registration

   In some circumstances, it is appropriate to note a URI scheme that
   was once in use or registered but for whatever reason is no longer in
   common use or the use is not recommended.  In this case, it is
   possible for an individual to request that the URI scheme be
   registered (newly, or as an update to an existing registration) as
   'historical'.  Any scheme that is no longer in common use MAY be
   designated as historical; the registration should contain some
   indication to where the scheme was previously defined or documented.











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5.  URI Scheme Registration Procedure

5.1.  General

   The URI registration process is described in the terminology of [3].
   The registration process is an optional mailing list review, followed
   by "Expert Review".  The registration request should note the desired
   status.  The Designated Expert will evaluate the request against the
   criteria of the requested status.  In the case of a permanent
   registration request, the Designated Expert may:

   o  Accept the URI scheme name for permanent registration.
   o  Suggest provisional registration instead.
   o  Request IETF review and IESG approval; in the meanwhile, suggest
      provisional registration.

   URI scheme definitions contained within other IETF documents
   (Informational, Experimental, or Standards-Track RFCs) must also
   undergo Expert Review; in the case of Standards-Track documents,
   permanent registration status approval is required.

5.2.  Registration Procedures

   Someone wishing to register a URI scheme SHOULD:

   1.  Check the IANA URI scheme registry to see whether or not there is
       already an entry for the desired name.  If there is already an
       entry under the name, choose a different URI scheme name.
   2.  Prepare a URI scheme registration template, as specified in
       Section 5.4.  The URI scheme registration template may be
       contained in an Internet Draft, alone or as part of some other
       protocol specification.  The template may also be submitted in
       some other form (as part of another document or as a stand-alone
       document), but the contents will be treated as an "IETF
       Contribution" under the guidelines of RFC 3978 [4].
   3.  Send a copy of the template or a pointer to the containing
       document (with specific reference to the section with the
       template) to the mailing list uri-review@ietf.org, requesting
       review.  In addition, request review on other mailing lists as
       appropriate.  For example, general discussion of URI syntactical
       issues could be discussed on uri@w3.org; schemes for a network
       protocol could be discussed on a mailing list for that protocol.
       Allow a reasonable time for discussion and comments.  Four weeks
       is reasonable for a permanent registration requests.
   4.  Respond to review comments and make revisions to the proposed
       registration as needed to bring it into line with the guidelines
       given in this document.




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   5.  Submit the (possibly updated) registration template (or pointer
       to document containing it) to IANA at iana@iana.org, specifying
       whether 'permanent' or 'provisional' registration is requested.

   Upon receipt of a URI scheme registration request,

   1.  IANA checks the submission for completeness; if sections are
       missing or citations are not correct, IANA rejects the
       registration request.
   2.  IANA checks the current registry for a entry with the same name;
       if such a registry exists, IANA rejects the registration request.
   3.  IANA requests Expert Review of the registration request against
       the corresponding guidelines.
   4.  The Designated Expert may request additional review or
       discussion, as necessary.
   5.  If Expert Review recommends registration 'provisional' or
       'permanent' registration, IANA adds the registration to the
       appropriate registry.
   6.  Unless Expert Review has explicitly rejected the registration
       request within two weeks, IANA should automatically add the
       registration in the 'provisional' registry.

   Either based on an explicit request or independently initiated, the
   Designated Expert or IESG may request the upgrade of a 'provisional'
   registration to a 'permanent' one.  In such cases, IANA should move
   the corresponding entry from the provisional registry.

5.3.  Change Control

   Registrations may be updated in each registry by the same mechanism
   as required for an initial registration.  In cases where the original
   definition of the scheme is contained in an IESG-approved document,
   update of the specification also requires IESG approval.

   Provisional registrations may be updated by the original registrant
   or anyone designated by the original registrant.  In addition, the
   IESG may reassign responsibility for a provisional registration
   scheme, or may request specific changes to a scheme registration.
   This will enable changes to be made to schemes where the original
   registrant is out of contact, or unwilling or unable to make changes.

   Transition from 'provisional' to 'permanent' status may be requested
   and approved in the same manner as a new 'permanent' registration.
   Transition from 'permanent' to 'historical' status requires IESG
   approval.  Transition from 'provisional' to 'historical' may be
   requested by anyone authorized to update the provisional
   registration.




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5.4.  URI Scheme Registration Template

   This template describes the fields that must be supplied in a URI
   scheme registration request:

   URI scheme name.
      See Section 2.8 for guidelines.
   Status.
      This reflects the status requested, and should be one of
      'permanent', 'provisional', or 'historical'.
   URI scheme syntax.
      See Section 2.2 for guidelines.
   URI scheme semantics.
      See Section 2.3 and Section 2.4 for guidelines.
   Encoding considerations.
      See Section 2.3 and Section 2.6 for guidelines.
   Applications/protocols that use this URI scheme name.
      Applications and/or protocols that use this URI scheme name; see
      Section 2.5.
   Interoperability considerations.
      If you are aware of any details regarding your scheme that might
      impact interoperability, please identify them here.  For example:
      proprietary or uncommon encoding method; inability to support
      multibyte character sets; incompatibility with types or versions
      of any underlying protocol.
   Security considerations.
      See Section 2.7 for guidelines.
   Contact.
      Person (including contact information) to contact for further
      information.
   Author/Change controller.
      Person (including contact information) authorized to change this,
      if a provisional registration.
   References.
      Include full citations for all referenced documents.  Registration
      templates for provisional registration may be included in an
      Internet Draft; when the documents expire or are approved for
      publication as an RFC, the registration will be updated.

6.  IANA Considerations

   This document replaces the current "URL Scheme" registry with a new
   Uniform Resource Identifier scheme registry, and establishes a new
   registration template and a new process for registration.  The
   process is based on [3] "Expert Review" with an initial (optional)
   mailing list review.





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   The template has an additional field for the status of the URI name
   scheme, and the procedures for entering new name schemes have been
   augmented.  Section 5 establishes the process for new URI scheme
   registration.

   To transition to the new registry, all URL name schemes in the
   existing table should be entered as URI schemes, with 'permanent'
   status.

7.  Security Considerations

   All registered values are expected to contain accurate security
   consideration sections; 'permanent' registered scheme names are
   expected to contain complete definitions.

   Information concerning possible security vulnerabilities of a
   protocol may change over time.  Consequently, claims as to the
   security properties of a registered URI scheme may change as well.
   As new vulnerabilities are discovered, information about such
   vulnerabilities may need to be attached to existing documentation, so
   that users are not misled as to the true security properties of a
   registered URI scheme.

8.  Acknowledgements

   Many thanks to Paul Hoffmann, Ira McDonald, Roy Fielding, Stu Weibel,
   Tony Hammond, Charles Lindsey, Mark Baker, and other members of the
   uri@w3.org mailing list for their comments on earlier versions.

   Parts of this document are based on [7], [8] and [10].  Some of the
   ideas about use of URIs were taken from the "Architecture of the
   World Wide Web" [11].



















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9.  References

9.1.  Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Moats, R., "URN Syntax", RFC 2141, May 1997.

   [3]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
        Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.

   [4]  Bradner, S., "IETF Rights in Contributions", BCP 78, RFC 3978,
        March 2005.

   [5]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
        Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
        January 2005.

   [6]  Duerst, M. and M. Suignard, "Internationalized Resource
        Identifiers (IRIs)", RFC 3987, January 2005.

9.2.  Informative References

   [7]   Petke, R. and I. King, "Registration Procedures for URL Scheme
         Names", BCP 35, RFC 2717, November 1999.

   [8]   Masinter, L., Alvestrand, H., Zigmond, D., and R. Petke,
         "Guidelines for new URL Schemes", RFC 2718, November 1999.

   [9]   Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
         "Uniform Resource Names (URN) Namespace Definition Mechanisms",
         BCP 66, RFC 3406, October 2002.

   [10]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
         Procedures for Message Header Fields", BCP 90, RFC 3864,
         September 2004.

   [11]  W3C Technical Architecture Group, "Architecture of the World
         Wide Web, Volume One", December 2004,
         <http://www.w3.org/TR/webarch/>.










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Authors' Addresses

   Tony Hansen
   AT&T Laboratories
   200 Laurel Ave.
   Middletown, NJ  07748
   USA

   EMail: tony+urireg@maillennium.att.com


   Ted Hardie
   Qualcomm, Inc.
   675 Campbell Technology Parkway
   Campbell, CA
   USA

   EMail: hardie@qualcomm.com


   Larry Masinter
   Adobe Systems
   345 Park Ave
   San Jose, CA  95110
   US

   Phone: +1 408 536 3024
   EMail: LMM@acm.org
   URI:   http://larry.masinter.net






















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Full Copyright Statement

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   ietf-ipr@ietf.org.

Acknowledgement

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).







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