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Versions: (draft-saintandre-urnbis-2141bis) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 RFC 8141

URNBIS                                               P. Saint-Andre, Ed.
Internet-Draft
Obsoletes: 2141 (if approved)                           January 23, 2014
Intended status: Standards Track
Expires: July 27, 2014


                   Uniform Resource Name (URN) Syntax
                  draft-ietf-urnbis-rfc2141bis-urn-07

Abstract

   A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI)
   that is intended to serve as a persistent, location-independent
   resource identifier.  This document defines the canonical syntax for
   URIs under the "urn" scheme, guidelines for URN namespaces,
   requirements for URN presentation and transmission, and methods for
   determining URN equivalence.  This document obsoletes RFC 2141.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on July 27, 2014.

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
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   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  URN Syntax  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Namespace Identifier Syntax . . . . . . . . . . . . . . .   4
     4.2.  Namespace Specific String Syntax  . . . . . . . . . . . .   4
     4.3.  Query Component and Fragment Identifier Component . . . .   4
   5.  URN Presentation and Transport  . . . . . . . . . . . . . . .   5
   6.  Equivalence of URNs . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Procedure . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.2.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Handling of URNs by URI Processors  . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Appendix A.  Changes from RFC 2141  . . . . . . . . . . . . . . .   8
   Appendix B.  Contributors . . . . . . . . . . . . . . . . . . . .   9
   Appendix C.  Acknowledgements . . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI)
   [RFC3986] that is intended to serve as a persistent, location-
   independent resource identifier.  This document defines the canonical
   syntax for URIs under the "urn" scheme, guidelines for URN
   namespaces, requirements for URN presentation and transmission, and
   methods for determining URN equivalence.




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   URNs were originally defined in [RFC2141].  The goal of this document
   is to specify URNs with the smallest reasonable set of changes from
   the original definition while ensuring consistency with the updated
   specification of URIs in [RFC3986].

   This document obsoletes RFC 2141.

2.  Terminology

   Several important terms used in this document are defined in the URI
   specification [RFC3986].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

3.  Requirements

   The requirements for URNs are specified in [RFC1737].  This document
   does not modify or update those requirements.

4.  URN Syntax

   The syntax for a URN is defined as follows using the Augmented
   Backus-Naur Form (ABNF) as specified in [RFC5234].

   namestring    = assigned-name [ "?" query ] [ "#" fragment ]
                 ;
                 ; query and fragment are defined in RFC 3986
                 ;
   assigned-name = "urn" ":" NID ":" NSS
                 ;
                 ; the URI scheme ("urn") is case-insensitive
                 ;
   NID           = (alphanum) 0*30(ldh) (alphanum)
                 ;
                 ; alphanum is defined in RFC 3986
                 ;
   ldh           = alphanum / "-"
   NSS           = 1*(pchar)
                 ;
                 ; pchar is defined in RFC 3986
                 ;


   The following sections describe provide additional information about
   these rules.



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4.1.  Namespace Identifier Syntax

   The syntax here is slightly more restrictive than what was defined in
   [RFC2141], since it forbids the character "-" at the end of a NID.

   NIDs are case insensitive (e.g., "ISBN" and "isbn" are equivalent).

4.2.  Namespace Specific String Syntax

   Depending on the rules governing a namespace, names that are valid in
   a namespace might contain characters that are not allowed in URNs
   according to the "pchar" rule (e.g., characters outside the ASCII
   range or characters that are reserved in URIs, such as "/", "?", and
   "#").  Such a string MUST be translated into a conformant NSS before
   using it as a protocol element or otherwise passing it on to other
   applications.  Translation is done by percent-encoding each
   disallowed character using the method defined in Section 2.1 of
   [RFC3986].  Note that the "%" character is allowed only for the
   purpose of percent-encoding.

   If a namespace designates one or more characters conforming to the
   "pchar" rule as having special meaning for that namespace (e.g., "@")
   and the namespace also uses that character in a literal sense, when
   used in a literal sense the character MUST be percent-encoded (e.g.,
   "%40").  For related considerations with regard to NID registration,
   see [I-D.ietf-urnbis-rfc3406bis-urn-ns-reg].

4.3.  Query Component and Fragment Identifier Component

   The URI specification [RFC3986] allows a query component, a fragment
   identifier component, or both after the path component of a URI,
   where the character '?' is used as a separator to denote the
   beginning of the query component and the character '#' is used as a
   separator to denote the beginning of the fragment identifier
   component.  The original URN syntax specification [RFC2141] reserved
   the '?' and '#' characters for future developments.  This
   specification aligns URN syntax with URI syntax by allowing the query
   component and fragment identifier component after (not within) the
   Namespace Specific String (NSS).

   This specification does not define the applicability and semantics of
   the query component or the fragment identifier component in URNs.
   Additional specifications might establish these matters for URN-
   related services (such as resolution) or for individual URN
   namespaces.  For example, it is possible that the query component
   might be used in requests to URN resolution services, or that the
   fragment identifier component might be used to distinguish the
   integral parts of resources named by URNs.  However, defining such



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   usage is left to specifications for URN resolution services,
   namespace registration requests and specifications for individual
   namespaces (which might use some namespace-specific syntax instead of
   the URI fragment identifier component), and other appropriate
   documentation (such as policy documents governing the management of a
   given URN namespace).

   Although URN assignment is a managed process (see
   [I-D.ietf-urnbis-rfc3406bis-urn-ns-reg]), the query component or
   fragment identifier component can be appended after the NSS once a
   URN has been assigned in accordance with the rules for a given
   namespace.

5.  URN Presentation and Transport

   The URN syntax defines the canonical format for URNs.  When URNs are
   transported and exchanged, they MUST be represented in this format.
   Further, all URN-aware applications MUST offer the option of
   displaying URNs in this canonical form to allow for direct
   transcription (for example by cut and paste techniques).  Such
   applications might support display of URNs in a more human-friendly
   form and might use a character set that includes characters that are
   not permitted in URN syntax as defined in this specification (e.g.,
   when displaying URNs to humans, such applications might replace
   percent-encoded strings with characters in an extended character set
   such as [UNICODE]).

6.  Equivalence of URNs

6.1.  Procedure

   For various purposes such as caching, often it is desirable to
   determine if two URNs are "the same".  This is done by testing for
   equivalence (see Section 6.1 of [RFC3986]).

   Two URNs are equivalent if they are octet-by-octet equal after
   applying case normalization (as specified in Section 6.2.2.1 of
   [RFC3986]) to the following constructs:

   1.  the URI scheme "urn"

   2.  the NID

   3.  any percent-encoded characters (see Section 2.1 of [RFC3986]) in
       the NSS






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   Percent-encoded characters MUST NOT be decoded, i.e., percent-
   encoding normalization (as specified in Section 6.2.2.2 of [RFC3986])
   MUST NOT be applied.

   If a query component, fragment identifier component, or both have
   been appended to the assigned URN, they MUST be ignored for purposes
   of determining equivalence.

   URN namespaces MAY define additional rules for equivalence, such as
   case-insensitivity of the NSS (or parts thereof).  Such rules MUST
   always have the effect of eliminating some of the false negatives
   obtained by the procedure above and MUST NOT result in treating two
   URNs as not equivalent if the procedure here says they are
   equivalent.  For related considerations with regard to NID
   registration, see [I-D.ietf-urnbis-rfc3406bis-urn-ns-reg].

6.2.  Examples

   The following URN comparisons (which use the "example" NID defined in
   [RFC6963]) highlight the equivalence rules:

   1.  URN:example:a123,456

   2.  urn:example:a123,456

   3.  urn:EXAMPLE:a123,456

   4.  urn:example:A123,456

   5.  urn:example:a123%2C456

   6.  URN:EXAMPLE:a123%2c456

   URNs 1, 2, and 3 are equivalent.  URN 4 is not equivalent to any of
   the other URNs in the above set.  URNs 5 and 6 are equivalent only to
   each other.

7.  Handling of URNs by URI Processors

   The URN syntax has been defined so that URNs can be used in places
   where URIs are expected.  A resolver that conforms to the URI
   specification [RFC3986] will extract a scheme of "urn" rather than a
   scheme value of "urn:<nid>".

   A URN MUST be considered an opaque URI by URI resolvers and passed
   (with the "urn" scheme) to a URN resolver for resolution.  The URN
   resolver can either be an external resolver that the URI resolver
   knows of, or it can be functionality built-in to the URI resolver.



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   To minimize user confusion, a URI browser SHOULD display the complete
   URN (including the "urn" scheme) to ensure that there is no confusion
   between URN namespace identifiers and URI scheme identifiers (e.g., a
   URI beginning with "urn:xmpp:" [RFC4854] is very different from a URI
   beginning with "xmpp:" [RFC5122]).

8.  IANA Considerations

   This section formally registers a URI scheme of 'urn'.

   [Note to RFC Editor: please replace "XXXX" with the number assigned
   to this document upon publication.]

   URI Scheme Name:  urn

   Status:  permanent

   URI Scheme Syntax:  See Section 4 of RFC XXXX.

   URI Scheme Semantics:  The 'urn' scheme identifies Uniform Resource
      Names, which are persistent, location-independent resource
      identifiers.

   Encoding Considerations:  See Section 4.2 of RFC XXXX.

   Applications/Protocols That Use This URI Scheme Name:  Uniform
      Resource Names are used in a wide variety of applications,
      including bibliographic reference systems and as names for
      Extensible Markup Language (XML) namespaces.

   Interoperability Considerations:  There are no known interoperability
      concerns related to use of the 'urn' URI scheme.

   Security Considerations:  See Section 9 of RFC XXXX.

   Contact:  URNBIS WG [mailto:urn@ietf.org]

   Author/Change Controller:  This scheme is registered under the IETF
      tree.  As such, the IETF maintains change control.

   References  None.

9.  Security Considerations

   This document specifies the syntax for URNs.  While some namespace
   resolvers might assign special meaning to certain of the characters
   of the Namespace Specific String, any security considerations
   resulting from such assignment are outside the scope of this



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   document.  For related considerations with regard to NID
   registration, see [I-D.ietf-urnbis-rfc3406bis-urn-ns-reg].

10.  References

10.1.  Normative References

   [I-D.ietf-urnbis-rfc3406bis-urn-ns-reg]
              Saint-Andre, P., "Uniform Resource Name (URN) Namespace
              Definition Mechanisms", draft-ietf-urnbis-rfc3406bis-urn-
              ns-reg-07 (work in progress), November 2013.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

10.2.  Informative References

   [RFC1737]  Sollins, K. and L. Masinter, "Functional Requirements for
              Uniform Resource Names", RFC 1737, December 1994.

   [RFC2141]  Moats, R., "URN Syntax", RFC 2141, May 1997.

   [RFC4854]  Saint-Andre, P., "A Uniform Resource Name (URN) Namespace
              for Extensions to the Extensible Messaging and Presence
              Protocol (XMPP)", RFC 4854, April 2007.

   [RFC5122]  Saint-Andre, P., "Internationalized Resource Identifiers
              (IRIs) and Uniform Resource Identifiers (URIs) for the
              Extensible Messaging and Presence Protocol (XMPP)", RFC
              5122, February 2008.

   [RFC6963]  Saint-Andre, P., "A Uniform Resource Name (URN) Namespace
              for Examples", BCP 183, RFC 6963, May 2013.

   [UNICODE]  The Unicode Consortium, "The Unicode Standard, Version
              6.3", 2013,
              <http://www.unicode.org/versions/Unicode6.3.0/>.

Appendix A.  Changes from RFC 2141

   This document makes the following substantive changes from [RFC2141]:



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   o  Allows the URI query component after the URN as assigned.

   o  Allows the URI fragment identifier component after the URN as
      assigned.

   o  Disallows "-" at the end of a NID.

   o  Allows the "~" and "&" characters in an NSS.

   o  Formally registers 'urn' as a URI scheme.

Appendix B.  Contributors

   Ryan Moats authored RFC 2141, which provided the basis for this
   document.

Appendix C.  Acknowledgements

   Many thanks to Leslie Daigle, Martin Duerst, Juha Hakala, Ted Hardie,
   Alfred Hoenes, John Klensin, Keith Moore, Julian Reschke, Lars
   Svensson, and other participants in the URNBIS WG for their input.

Author's Address

   Peter Saint-Andre (editor)

   Email: ietf@stpeter.im
























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