Network Working Group D. Orchard
Internet-Draft BEA Systems, Inc.
Expires: June 9, 2005 R. Salz
DataPower Technology, Inc.
December 9, 2004
The QName URN Namespace
draft-rsalz-qname-urn-00.txt
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Copyright (C) The Internet Society (2004).
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.
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Table of Contents
1. Introduction and Motivation . . . . . . . . . . . . . . . . . 3
2. Namespace Registration Template . . . . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . 5
4. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . 7
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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 [2] 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 [3].
Namespace ID:
qname
Registration Information:
Version number: 1
Registration date: 2004-11-30
Declared registrant of the namespace:
The W3C Technical
Architecture Group (TAG) [5],
reachable at tag@w3.org [6].
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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.
A QName URN is defined by the following ABNF [4]:
qnameURN = "qname" ":" prefix ":" localname ":" uri
prefix = ncname / "" / "*"
localname = ncname
uri = <any valid URI>
ncname = <see production 4 of [2]>
Here are three examples of a QName URN:
urn:qname:xkms:Reject:http://w3.org/2002/xkms#
urn:qname:Reject:http://w3.org/2002/xkms#
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:xkms="http://ww.w3.org/2002/xkms#">xkms:Reject</foo>
<foo xmlns="http://ww.w3.org/2002/xkms#">Reject</foo>
The third QName URN example would match at least both of the XML
QNames, as well as an inifinite number of others, since the
namespace prefix is explicitly marked as "don't-care."
Relevant ancillary documentation:
[1][2]
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 not 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
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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.
Scope:
Inherited from the original QName.
3. 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.
4 Normative References
[1] Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E. and F.
Yergeau, "Extensible Markup Language (XML) 1.0 (Third Edition)",
W3C Recommendation, February 2004,
<http://www.w3.org/TR/2004/REC-xml-20040204>.
[2] Bray, T., Hollander, D. and A. Layman, "Namespaces in XML", W3C
Recommendation, January 1990,
<http://www.w3.org/TR/1999/REC-xml-names-19990114>.
[3] Daigle, L., van Gulik, D., Iannella, R. and P. Faltstrom, "URN
Namespace Definition Mechanisms", BCP 33, RFC 2611, June 1999.
[4] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[5] <http://w3.org/2001/tag/>
[6] <mailto:tag@w3.org>
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Authors' Addresses
David Orchard
BEA Systems, Inc.
625 W 22nd Ave
Vancouver, BC V5Z 1Z5
Canada
Phone: +1 778-772-8425
EMail: dorchard@bea.com
URI: http://www.bea.com
Rich Salz
DataPower Technology, Inc.
1 Alewife Center
Cambridge, MA 02142
US
Phone: +1 617-864-0455
EMail: rsalz@datapower.com
URI: http://www.datapower.com
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