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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: Namespaces and XML validation
 John Cowan wrote: > This is quite separate from locality *as such*; locality of prefixes > just means that a given prefix isn't legal outside the scope of > its declaration. However, following the Algol precedents, you have > allowed declarations to supersede conflicting outer declarations > and to coexist with conflicting non-overlapping declarations. > There is some, if not overwhelming, software engineering experience > to indicate that this is a Bad Idea. > I find an assertion that "software engineering experience" has shown that Algol style lexical scoping is a bad idea quite surprising. Which school of software engineering believes this? Certainly not the one I went to. John -- I think you and some others on this list are being insufficiently imaginative in tackling the problem of figuring out how to validate documents that use the namespace spec. I believe it is possible to do fragment validation against DTDs, if that is so desired. However this certainly cannot be accomplished without some modification of the mechanics of DTD validation, as Tim outlined. I.e. pre-processing the DTD and the instance to convert all names to URI, name pairs, and what some have called fragment validation using as the root of each fragment any element that introduces a tag from a new namespace. A new namespace for this purpose is defined as one from a different namespace than its parent. I do not believe the new namespace proposal with local scoping makes it any harder to do than the old PI based namespace proposal. It may make it harder to think about it. The fact that the namespace prefix may actually be declared physically in the document after the DOCTYPE doesn't matter. At the time when the instance is to be compared to see if it matches the declaration in the DTD, the prefix to URI mapping is available. Can you do this without modifying your validation code? Certainly not. However, the approach I've outlined above still has a severe problem, which I don't think is so easily solved. In order to do this form of validaton, what gets put in the DTD is the prefix, and not the URI. That is a fatal flaw, because it makes it impossible to re-use a DTD for more than one document unless all documents that use that DTD use the same prefix for the same URI. That elevates the prefix to the same status as the URI -- something one must take care to keep globally unique. The prefix is not syntactically suited to this task. For that reason, and because of other well known deficiencies in DTDs, I think the issue of validation and namespaces is better dealt with in the context of a whole new schema language. The XML-Data submission clearly showed how this could work. The new namespace proposal does no violence to XML-Data's use of namespaces. I would therefore rather spend my time working on the new schema language, as the XML WG will shortly be doing, than patching DTDs. (The XSchema work that's been going on in XML-Dev is hopefully equally adaptable -- the volume of mail is simply too high so I have not been following it closely. The key is the use of XML syntax, which enables one to use namespace declarations in the schema in a manner that mimics the instance.) 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/ 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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