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Network Working Group                                         D. Orchard
Internet-Draft                                         Ayogo Games, Inc.
Expires: June 18, 2010                                           R. Salz
                                                                     IBM
                                                         J. Reschke, Ed.
                                                              greenbytes
                                                       December 15, 2009


                        The QName URN Namespace
                        draft-rsalz-qname-urn-01

Abstract

   This specification defines a Uniform Resource Name namespace for XML
   namespace-qualified names, QNames.  As long as the URN is encoded in
   the same character set as the document containing the original QName,
   the Qname URN provides enough information to maintain the semantics,
   and optionally the exact syntax, of the original name.

Editorial Note (To be removed by RFC Editor before publication)

   Please send comments to the xml-dev mailing list
   (<http://www.xml.org/xml-dev/>).

   XML versions, latest edits and the issues list for this document are
   available from
   <http://greenbytes.de/tech/webdav/#draft-rsalz-qname-urn>.

Status of this Memo

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

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Table of Contents

   1.  Introduction and Motivation  . . . . . . . . . . . . . . . . .  4
   2.  Namespace Registration Template  . . . . . . . . . . . . . . .  4
   3.  XML and Namespaces 1.1 . . . . . . . . . . . . . . . . . . . .  7
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   5.  Normative References . . . . . . . . . . . . . . . . . . . . .  7
   Appendix A.  Change Log (to be removed by RFC Editor before
                publication)  . . . . . . . . . . . . . . . . . . . .  8
     A.1.  Since draft-rsalz-qname-urn-00 . . . . . . . . . . . . . .  8
   Appendix B.  Open issues (to be removed by RFC Editor prior to
                publication)  . . . . . . . . . . . . . . . . . . . .  8
     B.1.  contacts . . . . . . . . . . . . . . . . . . . . . . . . .  8
     B.2.  mailing-list . . . . . . . . . . . . . . . . . . . . . . .  8
     B.3.  curie  . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     B.4.  qname-vs-expname . . . . . . . . . . . . . . . . . . . . .  9
     B.5.  i18n . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     B.6.  reg-info . . . . . . . . . . . . . . . . . . . . . . . . .  9
     B.7.  registrant . . . . . . . . . . . . . . . . . . . . . . . .  9
     B.8.  any-uri  . . . . . . . . . . . . . . . . . . . . . . . . .  9
     B.9.  examples . . . . . . . . . . . . . . . . . . . . . . . . . 10
     B.10. xml11  . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10




























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1.  Introduction and Motivation

   This specification defines a Uniform Resource Name namespace for XML
   namespace-qualified names, QNames.  As long as the URN is encoded in
   the same character set as the document containing the original QName,
   the Qname URN provides enough information to maintain the semantics,
   and optionally the exact syntax, of the original name.

   There are a variety of situations when a QName may need to be mapped
   to a URI.  For example, when exchanging (or referencing) an
   identifier for an XML element contained within a document, and the
   medium of exchange prefers URIs to QNames, such as an XML Schema
   anyURI data type.  Another scenario is for comparing the identifiers,
   which can be simpler by comparing just a string without having to
   also compare the context setting XML namespace attribute that may be
   declared arbitrarily earlier in the document.

   The XML Namespaces specification [XMLNS] does not provide a canonical
   mapping between QNames and URIs.  Any XML specification that wants to
   enable identifier exchanges must define a language specific QName to
   URI mapping.  There have emerged a variety of different algorithms
   and solutions for the mapping.  To date, there have been no
   standardized algorithms available that they can re-use, which has
   increased their efforts.  A standardized mapping, such as this,
   should provide increased productivity.

   Almost all of the algorithms for Qname to URI mappings are based upon
   concatenation of the URI and the name with variations based upon
   prefix inclusion, namespace name and name separator, etc.  These are
   typically problematic because it is difficult to recover the QName
   from the URI as the namespace name and name separator may have
   already been used in the namespace name.  Having the namespace name
   at the end of the identifier string avoids these and other problems.


2.  Namespace Registration Template

   The following paragraphs contain the URN namespace registration data,
   as defined in [RFC3406].

   Namespace ID:

      qname

   Registration Information:

      Version number: 1




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      Registration date: 2004-11-30

   Declared registrant of the namespace:

      The W3C Technical Architecture Group (TAG) [1], reachable at
      tag@w3.org [2].

   Declaration of syntactic structure:

      The QName URN is structured as four colon-separated fields.  Note
      that colons within the fourth field, the URI part, are not
      significant; the entire fourth field is treated as a single opaque
      entity by this URN scheme.

      The first field identifies the naming scheme.  The second contains
      the QName prefix, or an empty string if the QName comes from the
      default namespace, or an asterisk if the prefix is not
      significant.

      A QName URN is defined by the following ABNF [RFC5234]:

         qnameURN     = "qname" ":" prefix ":" localname ":" uri
         prefix       = ncname / "" / "*"
         localname    = ncname
         uri          = <any valid URI>
         ncname       = <see Production 4 of [XMLNS], Section 3>

      Here are three examples of a QName URN:

         urn:qname:foo:OK:http://example.com/ws/foo.xsd
         urn:qname::OK:http://example.com/ws/foo.xsd
         urn:qname:*:Reject:http://w3.org/2002/xkms#

      The first correspond to the following element content QNames (the
      element name is not significant):

         <foo xmlns:foo="http://example.com/ws/foo.xsd">foo:OK</foo>
         <foo xmlns="http://example.com/ws/foo.xsd">foo:OK</foo>

      The third example would match both of the others, as well as an
      inifinite number of QNames, since the namespace prefix is
      explicitly marked as "don't-care."

   Relevant ancillary documentation:

      [XML] [XMLNS]





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   Identifier uniqueness considerations:

      An XML QName is semantically defined as a (namespace-uri,
      localname) pair; the namespace prefix is not significant.  For
      some applications, such as signature functions, the prefix is
      important and must be preserved.

      The QName URN provides both a one-to-one mapping, that preserves
      the uniquess of the underlying QName, and an explicit many-to-one
      mapping, that does not preserve the uniquess when it is not
      important to do so.

   Identifier persistence considerations:

      QName URN's have the same persistance as the underlying XML QName
      from which they are derived.

   Process of identifier assignment:

      Assignment of identifiers depends on the original XML QName,
      typically deferring to the namespace URI.  Anyone with access to
      an XML QName can create an equivalent QName URN; no registration
      is required.

   Process for identifier resolution:

      Inherited from the QName resolution rules (typically the namespace
      URI) from which the QName URN is created.

   Rules for Lexical Equivalence:

      If necessary, convert each QName URN to the same encoding.  The
      encoding of a QName URN is determined by context, and depends on
      the encoding of the document in which it appears.

      To be lexically equivalent the resultant QName URN's must be
      identical when compared byte-for-byte.  To be semantically
      equivalent, ignore the prefix field when comparing bytes.

   Conformance with URN Syntax:

      Fully conformant.

   Validation mechanism:

      Inherited from the namespace URI of the original QName.





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   Scope:

      Inherited from the original QName.


3.  XML and Namespaces 1.1

   This scheme can also support the XML 1.1 [XML11] and XML namespaces
   1.1 [XMLNS11] standards.

   In the 1.1 Namespace specification, namespace URI's (universal
   resource identifiers; see ...xref...) become IRI's (internationalized
   resource identifiers, see ...xref...).  Although currently an
   Internet-Draft, and therefore not feasible to use as a normative
   reference here, it is expected that the final RFC will continue to
   define a way to map IRI's to URI's.  To apply this specification to
   IRI's, then, first apply that mapping before using the syntax here.


4.  Security Considerations

   QName URN's provide a way to transcribe XML QName's into and out of
   URN syntax.  Any security considerations are inherited from the
   original QName.


5.  Normative References

   [XML]      Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and
              F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
              Edition)", W3C REC-xml-20081126, November 2008,
              <http://www.w3.org/TR/2008/REC-xml-20081126/>.

   [XML11]    Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E.,
              Yergeau, F., and J. Cowan, "Extensible Markup Language
              (XML) 1.1 (Second Edition)", W3C REC-xml11-20060816,
              August 2006,
              <http://www.w3.org/TR/2006/REC-xml11-20060816/>.

   [XMLNS]    Bray, T., Hollander, D., Layman, A., Tobin, R., and H.
              Henry, "Namespaces in XML 1.0 (Third Edition)", W3C REC-
              xml-names-20091208, December 2009,
              <http://www.w3.org/TR/2009/REC-xml-names-20091208/>.

   [XMLNS11]  Bray, T., Hollander, D., Layman, A., and R. Tobin,
              "Namespaces in XML (Second Edition)", W3C REC-xml-names11-
              20060816, August 2006,
              <http://www.w3.org/TR/2006/REC-xml-names11-20060816/>.



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   [RFC3406]  Daigle, L., van Gulik, D., Iannella, R., and P. Faltstrom,
              "Uniform Resource Names (URN) Namespace Definition
              Mechanisms", BCP 33, RFC 3406, October 2002.

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

   [1]  <http://w3.org/2001/tag/>

   [2]  <mailto:tag@w3.org>


Appendix A.  Change Log (to be removed by RFC Editor before publication)

A.1.  Since draft-rsalz-qname-urn-00

   Updated references and fix reference to XMLNS which was meant to
   reference XMLNS11.  Add a set of issues: "any-uri", "contacts",
   "curie", "examples", "i18n", "mailing-list", "qname-vs-expname",
   "reg-info", "registrant", "xml11".


Appendix B.  Open issues (to be removed by RFC Editor prior to
             publication)

B.1.  contacts

   Type: edit

   julian.reschke@greenbytes.de (2009-12-11): Update author information.

B.2.  mailing-list

   Type: edit

   julian.reschke@greenbytes.de (2009-12-12): In the boilerplate, state
   where this Internet Draft should be discussed.  Proposal: xml-dev.

B.3.  curie

   Type: edit

   julian.reschke@greenbytes.de (2009-12-12): Maybe we should clarify
   the relation with CURIEs (which can be confused with QNames)?







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B.4.  qname-vs-expname

   Type: edit

   julian.reschke@greenbytes.de (2009-12-12): There's a risk that we
   confuse people by claiming this is about QNames.  What we map to URNs
   is the triple (namespace-name, local-name, prefix), where the prefix
   is optional.  The tuple (namespace-name, local-name) is the *expanded
   name*, not the QName.  Options: (1) just clarify the prose, (2)
   rename the URN scheme (is it in use already?) to something like
   "xmlname".

B.5.  i18n

   Type: change

   julian.reschke@greenbytes.de (2009-12-11): Need to state how non-
   ASCII characters are mapped to the URN.

B.6.  reg-info

   In Section 2:

   Type: edit

   julian.reschke@greenbytes.de (2009-12-11): Update registration info.

B.7.  registrant

   In Section 2:

   Type: edit

   julian.reschke@greenbytes.de (2009-12-11): Update registrant info.

B.8.  any-uri

   In Section 2:

   Type: change

   julian.reschke@greenbytes.de (2009-12-12): Need a grammar for "any
   valid URI".  Do we follow stricly XMLNS, which would make it a "URI
   reference" as per RFC 3986, or do we tolerate junk and/or IRIs (no
   offense).  Also, we need to state that this part of the URN will be
   empty for elements that are in no namespace (right?).





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B.9.  examples

   In Section 2:

   Type: change

   julian.reschke@greenbytes.de (2009-12-11): Having just examples of
   QNames in element content might be confusing to people not familiar
   with that use case; we also should have at least one example for an
   XML element name, and for a QName in content. (potentially also move
   the examples out of the registration template?)

B.10.  xml11

   Type: change

   julian.reschke@greenbytes.de (2009-12-11): Consider removing any
   material related to XML 1.1.


Authors' Addresses

   David Orchard
   Ayogo Games, Inc.

   Email: orchard@pacificspirit.com


   Rich Salz
   IBM

   Email: rsalz@us.ibm.com


   Julian F. Reschke (editor)
   greenbytes GmbH
   Hafenweg 16
   Muenster, NW  48155
   Germany

   Email: julian.reschke@greenbytes.de
   URI:   http://greenbytes.de/tech/webdav/









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