- From: Jan Mendling <mendling@web.de>
- Date: Tue, 7 Jan 2003 02:24:34 +0100
- To: noah_mendelsohn@us.ibm.com, xmlschema-dev@w3.org
Hi Noah and the others, I do not think that W3C XML Schema needs something like tree grammar too much, although a relaxation of the Unique Particle Attribution Rule forbidding nondeterministic content models would be a plus. Currently I have a problem, which I do not know how to express with any sort of tree grammar. Consider the following: ... <Arc FromId="1" ToId="2"/> <Arc FromId="2" ToId="1"/> <Arc FromId="1" ToId="2"/> ... I want to detect whether (1) there are other Arc elements with the @FromId (Arc1) being equal to their @ToId (ArcX) and their @FromId (ArcX) being equal to the @ToId (Arc1). This can be expressed with Schematron's XPath Assertions. You could argue that I could model my content structure in a different way, so that grammars might capture these properties. But this is often counterproductive in terms of readability. Therefore, I think a flexible and user-friendly solution would be to have something like Schematron assertions in W3C XML Schema. And as XPath as a W3C standard is involved, I cannot imagine that there will be too much overhead in calculation. Or am I wrong? It would be nice to have some ideas here from a formal language point of view! Greets, Jan noah_mendelsohn@us.ibm.com schrieb am 07.01.03 00:24:27: > >> you are absolutely right that the expressiveness of XML > >> schema constraints should be improved > > I agree. > > >> and XPath seems to be a natural option. > > Yes, though certainly other options (Relax-like tree > automata, something else grammar-based, etc.) should at > least be considered before a decision is made. I agree > that XPath is a likely good choice. > > > About performance: I think performance matters should > > not guide the decision about wheter XPath-Constraints > > should be added to the schema specification or not. If > > performance is a matter then people can switch of > > validation (or use only simple constraints). > > Here I respectfully but strongly disagree. It's > essentially that my customers and those with whom they > do business get consistent results when they validate a > given document with a given schema. If they say "Well, > it was valid with XYZ-Corp.'s high performanc processor > but not ABC's" we've got a mess. The main reason to > use XML is universal consistency and interop. High > performance schema processing is very, very important > to IBM's customers, as is consistency of semantics. I > think we can get better co-occurrence constraints > without sacrificing performance. > > ------------------------------------------------------------------ > Noah Mendelsohn Voice: 1-617-693-4036 > IBM Corporation Fax: 1-617-693-8676 > One Rogers Street > Cambridge, MA 02142 > ------------------------------------------------------------------ > > -- ~~~~~~~~~~~~~ ~ Jan Mendling ~ Güterstr.53 ~ 54295 Trier ~ 0175-1636958 ~~~~~~~~~~~~~ ______________________________________________________________________________ Die vCard - Ihr neues Kennzeichen - bei WEB.DE FreeMail! http://freemail.web.de/features/?mc=021156
Received on Monday, 6 January 2003 20:25:07 UTC