- From: <noah_mendelsohn@us.ibm.com>
- Date: Tue, 16 Oct 2007 22:15:04 -0400
- To: Philippe Poulard <philippe.poulard@sophia.inria.fr>
- Cc: "'George Cristian Bina'" <george@oxygenxml.com>, Michael Kay <mike@saxonica.com>, "'wayne liu'" <waynix@gmail.com>, xmlschema-dev@w3.org
Perhaps the confusion here is about terminology. More or less in keeping with the precedent of XML 1.0 and DTDs, XML Schema uses the term "content model" in a very specific way, which is to refer to the combinations of sequences, choices and all groups provided by the language. From that point of view, the new assertion facility is completely separate. In other respects the two are quite symmetric in their affect on validation: to be valid per a type, the content must satisfy both the "content model" in the sense given above, and the assertions. The only asymmetry I'm aware of is that the XPath 2.0 expressions used in the assertions can depend in some cases on the types (such as integer) of the elements and attributes tested, and those types are typically assigned and tested as a byproduct of content model validation. If your XPath doesn't rely on such type assignment, then content models and assertions contribute pretty much symmetrically. As to helping out an editor, it's usually the case that it is easier to infer information from simpler languages, and the regular expressions that underly schema content models are in that sense quite simple. If I say choice(a,b,c) it's indeed easy for an editor to know to prompt for an a, b, or c. Then again, nothing prohibits an editor from recognizing certain simple XPath expressions you might use in an assertion check and doing very similar prompting. Indeed, I'd expect many assertions to be quite simple, such as @a > @b, and I wouldn't be surprised that it would be quite easy for a schema-directed editor to help you enter an a that's greater than b. Finally, Michael Kay is right in my opinion: XPath is a declarative language. It is neither imperative nor Turing-complete. If these subject's are of concern, you might also be interested in reading the TAG's finding called the Rule of Least Power [1], which was written by Tim Berners-Lee with a little editorial help from me. Noah [1] http://www.w3.org/2001/tag/doc/leastPower.html -------------------------------------- Noah Mendelsohn IBM Corporation One Rogers Street Cambridge, MA 02142 1-617-693-4036 --------------------------------------
Received on Wednesday, 17 October 2007 02:14:03 UTC