[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Schemas, transformations and algebras
One way of thinking about a schema (using "schema" in its generic sense rather than to refer to WXS, RNG, DTDs etc.) is as defining a possibly infinite set of document instances. And one way of thinking about a transformation (again, in its generic sense rather than to refer specifically to XSLT) is as defining a function from one set of documents/schema (the domain of the transformation) to another set/schema (the codomain). Thinking this way we can use functional notation for transforms, eg., t: S1 -> S2 saying that transformation t takes members/instances of S1 onto members/instances of S2. Now, suppose we want to compose two transforms, t1: S1 -> S2 t2: S3 -> S4 to get, t3: S1 -> S4 In general we can only do this if S2 is a subset of S3. However, if the intersection of S2 and S3 is at least non-empty we can compose a restriction of t1 with t2, ie., where S1' is a subset of S1 and S2' is the image of S1' under t1 and S2' is a subset of S3 we can compose, t1/S1': S1' -> S2' t2: S3 -> S4 to get, t3/S1': S1' -> S4 So far so good. But my question is, how, using the various XML schema languages, can I specify the restricted schema S1'? I'm fairly sure that this is straightforward to do in WXS using derivation by restriction. And I'm sure it can't be done with DTDs (you'd have to construct a completely new DTD to get the same effect). What I'm not sure about is whether or not there's any mechanism for this in RNG. Is there? If not, should there be? Am I right wrt WXS? Cheers, Miles
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