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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] fixing (just) namespaces and validation
 I brought this up earlier on a list of things that could be done to improve XML, and it keeps ringing in my ears. Namespaces and validation are incompatible in cases where the namespace prefix changes for whatever reason, because XML 1.0 will validate based only on the prefix. The Namespaces in XML Recommendation doesn't even provide a mechanism for telling DTDs what URI might be associated with a given prefix. James Clark provides an explanation of this at http://www.jclark.com/xml/xmlns.htm: >It would of course be very useful to have namespace-aware validation: >to be able to associate each URI used in a universal name with some >sort of schema (similar to a DTD) and be able to validate a document >using multiple such URIs with respect to the schemas for all of the URIs. >The XML Namespaces Recommendation does not provide this. The reason is >is that DTDs have many other problems and missing features in addition >to lack of namespace-awareness. So the plan is to come up with a new >schema mechanism that fixes the problems with DTDs and, as part of this, >provides namespace-awareness. This work is being done by the XML Schema WG. At the same time, Namespaces REC says: (end of Section 6, conformance) >Thus, unless the use of a validating processor has been specified, >there can be no assurance that the contents of attribute values >have been checked for conformance to this specification. Most people seem to have disregarded this notice, and use non-validating processors when they use namespaces, if indeed they do use namespaces. Those who validate simply pray that in these early days of XML processing no one will have gotten around to changing a prefix for whatever reason. It seems like DTDs will be here for a while, and it doesn't seem like fixing this problem is difficult. The PI from the 5/18 draft, which was meant for documents, would serve just as well in DTDs. It could provide a simple mapping for prefixes as used in the DTD to the namespace URI, allowing processors to validate against both the namespace URI and the local part, rather than simply the element or attribute name. For example: (Yes, I changed the colon to a dash.) <?xml-namespace ns="http://www.simonstl.com/ns/1999/xpdl" prefix="xpdl"?> When it appeared in the DTD, this would tell a validating processor that the prefix xpdl maps to http://www.simonstl.com/ns/1999/xpdl. If the processor then encountered elements with a namespace URI of http://www.simonstl.com/ns/1999/xpdl, it could validate them on the basis of that URI and the local part even if the xpdl prefix had disappeared. It seems very simple, even potentially worthwhile. I don't think that it would give parser builders enormous headaches, and it would take away a lot of the technical ammunition of the anti-namespaces crowd. Then we could discuss the more painful issues of 'what does it mean?' without extra noise about how weakly it's been implemented, and we wouldn't have to wait as impatiently for the Schema WG to finish their labors. Simon St.Laurent XML: A Primer (2nd Ed - September) Building XML Applications Inside XML DTDs: Scientific and Technical Sharing Bandwidth / Cookies http://www.simonstl.com xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1 To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...) 
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