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Re: internal schema?
Date: 12/14/2005 12:30:00 AM
On Fri, 2005-12-09 at 04:03, Nagarajan K wrote: > In dtd we can have internal or external > type. What about schema. But schema is xml > document . can we have internal schema In principle, yes. The XML Schema 1.0 spec does not constrain the set of locations where a processor can look for schema documents, and carrying both a payload to be validated and a set of schema documents which describe it in the same XML envelope is certainly legal. In practice, there are a few complications: 1 Since the spec does not constrain how processors look for schema documents, no processor is required to understand any particular URI scheme or way of referring to schema documents. 2 To point at inline schemas, you'll probably want to use URIs which use fragment identifiers. The official definition of frgragment identifiers for XML documents lags behind current practice by several years; although many XML processors understand bare-name fragment identifiers to refer to IDs, I am not sure whether the relevant IETF documents actually require this. And of course ID attributes can only be declared in a DTD, and the designers of SOAP have decided that DTDs must not be used in SOAP messages, so if you are planning to use SOAP, you are in a bind. 3 Normally, one would want to use inline schemas on just the payload, not on the entire XML document. From the point of the view of the XML Schema 1.0 spec, this is not a problem. In practice, though, some schema processors will only start schema validation at the root of the XML document, and there is in any case no standard way of telling them to start anywhere else. 4 Different processors which do support inline schemas have different ways of finding them and allowing the user to specify at invocation time that they should be used. It's been a long time since I looked into this, but my recollection is that some processors required points of one form, others required a different (incompatible) form, and one processor simply assumed that any schema document (i.e. xsd:schema element) in the XML document should be used. There was an attempt a couple of years ago to persuade the XML Schema Working Group to form a task force to investigate what current processors do and write a short Note describing current practice (and possibly recommending some common practice, if the WG could agree on what to recommend), but some WG members opposed any such Note and the idea went nowhere. I hope this helps. -C. M. Sperberg-McQueen From noah_mendelsohn@u... Wed Dec 14 15:38:01 2005 Received: from aji.w3.org ([188.8.131.52]