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Versions: (RFC 2141) 00 draft-saintandre-urnbis-2141bis

URNBIS                                               P. Saint-Andre, Ed.
Internet-Draft                                       Cisco Systems, Inc.
Obsoletes: 2141 (if approved)                                   R. Moats
Intended status: Standards Track                        October 13, 2012
Expires: April 16, 2013


                   Uniform Resource Name (URN) Syntax
                      draft-saintandre-2141bis-00

Abstract

   A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI)
   that is intended to serve as a persistent, location-independent
   resource identifier.  The general class of URNs is differentiated
   from all other URIs through the use of the 'urn' URI scheme.  This
   document defines the canonical syntax for URNs, 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.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 16, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  URN Syntax  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
     4.1.  Namespace Identifier Syntax . . . . . . . . . . . . . . . . 4
     4.2.  Namespace Specific String Syntax  . . . . . . . . . . . . . 4
   5.  URN Presentation and Transport  . . . . . . . . . . . . . . . . 5
   6.  Lexical Equivalence in URNs . . . . . . . . . . . . . . . . . . 5
     6.1.  Procedure . . . . . . . . . . . . . . . . . . . . . . . . . 5
     6.2.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . 5
   7.  Functional Equivalence in URNs  . . . . . . . . . . . . . . . . 6
   8.  Handling of URNs by URI Processors  . . . . . . . . . . . . . . 6
   9.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     11.1. Normative References  . . . . . . . . . . . . . . . . . . . 7
     11.2. Informative References  . . . . . . . . . . . . . . . . . . 7
   Appendix A.  Changes from RFC 2141  . . . . . . . . . . . . . . . . 8
   Appendix B.  Acknowledgements . . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8























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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.  The general class of URNs is
   differentiated from all other URIs through the use of the 'urn' URI
   scheme.  This document defines the canonical syntax for URNs,
   guidelines for URN namespaces, requirements for URN presentation and
   transmission, and methods for determining URN equivalence.

   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].  If approved, this document will
   obsolete RFC 2141.

   The discussion venue for this specification is the mailing list of
   the URNBIS Working Group; further information can be found at
   <https://www.ietf.org/mailman/listinfo/urn>.


2.  Terminology

   Many 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].









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      URN       = "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.

4.1.  Namespace Identifier Syntax

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

   NIDs are case insensitive (e.g., "ISBN" and "isbn" identify the same
   namespace).

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 urnchar 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 [RFC3986].

   The "%" character is allowed only for the purpose of percent-
   encoding.

   If a namespace designates one or more characters conforming to the
   urnchar 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 [RFC3406].





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5.  URN Presentation and Transport

   The URN syntax defines the canonical format for URNs.  All URN
   transport and interchanges MUST take place 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 RFC (i.e., when displaying URNs to humans,
   such applications might replace percent-encoded strings with
   characters in an extended character set such as Unicode).


6.  Lexical Equivalence in 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
   "lexical equivalence".

   Two URNs are lexically equivalent if they are octet-by-octet equal
   after the following preprocessing rules:

   1.  normalize the case of the URI scheme "urn"
   2.  normalize the case of the NID
   3.  normalize the case of any percent-encoding

   Note: Percent-encoded characters MUST NOT be decoded.

   URN namespaces MAY define additional rules for lexical 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 [RFC3406].

6.2.  Examples

   The following URN comparisons highlight the lexical equivalence
   rules:

   1.  URN:foo:a123,456
   2.  urn:foo:a123,456





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   3.  urn:FOO:a123,456
   4.  urn:foo:A123,456
   5.  urn:foo:a123%2C456
   6.  URN:FOO:a123%2c456

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


7.  Functional Equivalence in URNs

   Functional equivalence is determined within a given namespace and
   managed by resolvers for that namespace, and thus is beyond the scope
   of this document.  For related considerations with regard to NID
   registration, see [RFC3406].


8.  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.

   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 URL scheme identifiers.


9.  Security Considerations

   This document specifies the syntax for URNs.  While some namespaces
   resolvers may assign special meaning to certain of the characters of
   the Namespace Specific String, any security consideration resulting
   from such assignment are outside the scope of this document.  For
   related considerations with regard to NID registration, see
   [RFC3406].


10.  IANA Considerations

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



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

   URI Scheme Name:  urn
   Status:  permanent
   URI Scheme Syntax:  See Section 4 of RFCXXXX.
   URI Scheme Semantics:  The 'urn' scheme identifies Uniform Resource
      Names, which are persistent, location-independent resource
      identifiers.
   Encoding Considerations:  See Section 4.2 of RFCXXXX.
   Applications/Protocols That Use This URI Scheme Name:  Uniform
      Resource Names are used in a wide variety of applications,
      including bibliographical 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 RFCXXXX.
   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.


11.  References

11.1.  Normative References

   [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.

11.2.  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.

   [RFC3406]  Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
              "Uniform Resource Names (URN) Namespace Definition
              Mechanisms", BCP 66, RFC 3406, October 2002.




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Appendix A.  Changes from RFC 2141

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

   o  Disallowed "-" at the end of a NID.
   o  Allowed the "~" and "&" characters in an NSS.
   o  Formally registered 'urn' as a URI scheme.


Appendix B.  Acknowledgements

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

   Thanks to Julian Reschke for his corrections to the ABNF.


Authors' Addresses

   Peter Saint-Andre (editor)
   Cisco Systems, Inc.
   1899 Wynkoop Street, Suite 600
   Denver, CO  80202
   USA

   Phone: +1-303-308-3282
   Email: psaintan@cisco.com


   Ryan Moats





















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