Re: Proliferation of validation options
Francis Norton wrote: > Have these use cases been published? No as such. Some, like the ones in the Primer, and the schema for schemas, and XHTML are all very prominant examples, though. > For me the key element of > difficulty reading the part 1 spec is that it appears to be a complex > solution that has been abstracted out from the a lot of the problems it > is designed to solve. Technical specs are like novels, understanding > motivations casts light on everything. Yes. But the fat lady is still doing her voice warmups! Two problems which can be pretty clearly traced from feature back to use case are nullability and uniqueness/key constraints. These are obviously both database-related features first and foremost. I think the uniqueness/key mechanism owes a lot to keys in XSLT as far as its approach: people seem pretty happy with that. (Schematron has limited key support too, to a different end. RELAX only has IDs AFAIK.) But the current nullability mechanism (only element contents can be nulls?) looks a little arbitrarily limited to me: on the other hand, if we expanded into a full-blown exception-handling mechanism (so that the WF data could have exceptions and errors built in, and the receiving system could handle the data properly would help robustify distributed processing, but it would make the language more complicated and further away from people's expectations. (Schematron and RELAX have no nulls AFAIK.) It would be nice to see some discussion about whether a schema language for integration with SQL and Query languages needs nulls, and how to do it. Rick Jelliffe
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