[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: Namespace URI address resources
Rick Jelliffe wrote: > A schema is "processing" not "data": it is tied to whatever > applications > understand the schema format. Editing, creating and > validating against a > schema are all applications. I can't understand how the idea that schemas operate at the same level as Java classes and stylesheets has been introduced into this discussion. As far as I can see, one point of the schema proposal is to be functionally equivalent to a DTD with a few obvious advantages, one of these being that if we get the definition right, each node can specify its own schema. This makes the dynamic creation of documents that are made up of other documents a much more straightforward task (for example, as occurs in fragment interchange and transclusion), and, IMO, impossible without it. However, the fact that the schema can at its simplest play the role of the DTD means that it is used by the parser, not just the application. I use the terms here in the logical sense implied by XML 1.0; the parser will check the document for well-formedness and possibly validate it, the application will then make use of the document. So "editing, creating and validating against a schema" are NOT all applications - validating happens at a lower level. To look at it a different way, DTDs can also be used to write tools that edit and create documents but that does not detract from their fundamental role in the validation of documents. In other words, they are most definitely NOT on the same level as stylesheets, Java classes, or whatever. I think the problem we have is that validation is a special case of the use of namespaces. In normal circumstances you would validate the document and then pass it on for processing, and the processing application would make use of any namespaces present, as it wants. In other words there is a clear separation as to exactly where namespaces play a role. However, to allow documents to have a mixture of schemas (in the sense of DTD substitutes) we need to use namespaces to indicate which schema should be used. In other words, there needs to be some way of saying which namespace corresponds to which schema. Namespaces are therefore already playing a role at the level of parsing. This is incidentally why I don't PIs could be used for this, as some have suggested, since according to XML 1.0, PIs are passed through the parser to applications. But by then it's too late - we need the schema for validation. [IMHO I would even suggest it is more 'intuitive' anyway, to use the namespace attribute. Remember the original namespace debate that raged on this list? Everyone thought that namespaces WERE validation! It just seemed so ... well ... intuitive.] Regards, Mark Birbeck Mark.Birbeck@i... http://www.iedigital.net/ 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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