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Michael Kay wrote: > Or you could do it all with assertions - but the danger with complex > assertions is that the diagnostics when they are not satisfied can get > rather obscure. > Hence the criticality of natural language formulations of the intent of the assertion test. Which was the departure point for Schematron in 1999. The initial problem that computer scientists try to solve is how to represent something in a way that computers can understand. Then, as soon as that is answered, they realize that they have asked the wrong question, and they need to ask how to represent something in ways that both humans and computers can understand. I do think XSD is stuck asking that first question, and never getting to the second (or deferring it to implementations, as if good human text about the intentions and rationale of some constraint can be auto-generated from machine descriptions.) This relates to the patterns versus types point I tried to make the other day. Considering a document as a graph of nodes and arcs, XSD allows you to document nodes but not arcs. So there is nowhere to document why it is that two elements in a sequence should follow each other, for example. That becomes a comment of the type or parent, but even there it is odd. I think Schematron is equally strong (and equally weak) on documentation and constraints on arcs as well as nodes. Cheers Rick
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