- From: <noah_mendelsohn@us.ibm.com>
- Date: Tue, 18 Jun 2002 16:46:16 -0400
- To: www-tag@w3.org
Rick Jeliffe wrote: >> I agree with Tim Bray (and perhaps Noah Mendelsohn, >> in part) that the PSVI should be renamed. >> >> * First because it may not be PSV, as he says. >> >> * Second because it does not have a >> relationship-preserving re-serialization to XML >> (except of course by stripping out the augmentations >> and requiring validation again) and therefore is >> non-XML. PSVI does not draw out this discontinuity >> enough. >> >> * Third because "Schema" is a codeword for W3C XML >> Schemas, but other schema languages could be used. I am actually proposing an additional intermediate layer of Infoset. Today we have XML Infoset, which is a proper subset of the PSVI resulting from W3C Schema validation. What I am speculating is that a stack along the following lines would make sense: * XML Infoset (as we know it today) * Type-name-aware infoset: (details TBD) This would add type name information that could come the instance (e.g xsi:type) and/or validation with any schema language that used a consistent naming convention for types (presumably QNames). We'd have to think about whether type names should be specifieable for attributes or only for elements. xsi:type might have to be moved out of the Schema rec and into its own little rec, feeding the TAI without requiring validatin. * W3C XML Schema PSVI: As it exists in the Schema recommendation. This is what you use when your application really does want to know about defaults, reflected type definitions, what validated, and other data that is by its nature determined during validation. As I said, the whole point of validation is to learn information about the combination of a document and a schema. Formalizing that is a good thing (depending on that information when you shouldn't is what's potentially bad.) So, the TAI would take one or a few of the properties that are now only available in the PSVI, and make clear that their values can also sometimes be determined without doing W3C XML schema validation. Some care would be needed to avoid inconsistencies when validation is in fact done using a TAI as input. I suspect that's tractable, perhaps in a Schema 1.1 Rec. Tim Bray wrote: >> ... and if such a thing existed, presumably it's what >> XQuery/XPath ought to use, as opposed to its current >> contra-factual assertions that the only way to get >> types to use in queries is to apply a particular flavor >> of schema processor. Regardless of the layering, I think Query and XPath should give as much value as possible when used with well-formed documents. That means having a good story based only on the XML Infoset, or maybe on the TAI if that proves to be a good idea. Both can be determined only be inspecting the instance in isolation (well, in isolation of XML schemas -- you may still need external DTD, Entities, etc. if standalone=no). Given that starting point, I think the query group should ask: is there an even more valuable service we should provide in the case where validation is indeed to be performed? I'm neutral on that. If everything applications need can be done just knowing the names of types, then Query should depend only on TAI. If there is a more valueable service that can be performed using the additional information that's only available after validation, then that should be considered on the merits. There still should be the option to use query with just infoset/TAI, I.e. without doing validation. BTW: these are just my thoughts, don't represent IBM's corporate position, and haven't been coordinated with our XML Query team. On query matters, they can give you official positions. ------------------------------------------------------------------ Noah Mendelsohn Voice: 1-617-693-4036 IBM Corporation Fax: 1-617-693-8676 One Rogers Street Cambridge, MA 02142 ------------------------------------------------------------------
Received on Tuesday, 18 June 2002 17:04:28 UTC