[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: W3C XML Schema moves forward
Robin Cover wrote: > > Questions have been raised episodically about the usability of W3C's > 'XML Schema' formalism (http://www.w3.org/TR/xmlschema-1/): does it > attempt too much?, is the spec hard to understand?, is the notation > excessively verbose?, etc. Despite these doubts, the WD specification > seems to make sense to a growing number of developers. I note > (anecdotically) that W3C XML Schema (.xsd) is used as the principal > meta-level specification in two important projects, announced > recently: > > "DIG35: Metadata Standard for Digital Images" > http://www.oasis-open.org/cover/dig35.html > > "Universal Description, Discovery, and Integration (UDDI)" > http://www.oasis-open.org/cover/uddi.html > > These are not lightweight or trivial XML applications. The other factor at play is that the W3C XML Schema WG has tried (through the last call draft procedure, e.g.) to listen to comments that the spec is too hard, that the notation is excessively verbose, and even that it attempts too much (in some pet area) or too much (in some other pet area). XML Schemas is an evolving, and IMHO improving, target. I think the upcoming version will be much better received than the previous drafts: it has benefited from the extensive comments in exactly the kinds of areas Robin mentions. I have been very impressed by recent improvements, watching from afar: the editors are doing great jobs. However, *before* a spec is finalized *is* the appropriate time to pick nits, be they large or small! If an issue is important for a user, it is fair game to comment about it and try to influence XML Schemas in an improved direction. Just as with the last round, I encourage XML-DEV-ers to look critically and thoroughly at the upcoming specs: do they meet your needs? are they incomplete in any significant way that might allow vendors to trap you to their products? Can you do simple things simply? Can you use the elements and attributes and values in the ways you think are natural (is it methodology-free enough)? When I extract some data from a schema-ed document, can I do enough with it? What features in particular are definitely "too much"? Are the datatypes complete (should money be a built-in datatype, for example)? In the Candidate Release phase, it is almost too late to make general "I like this" or "I don't need that" comments: instead, I think the focus is more on getting implementation feedback: "this part of the spec is ambiguious", "this is good enough for now", "this part of the spec was hard to implement", "I tried to convert my DTD to XML Schemas and had difficulty because of such-and-such a reason", "the relation to W3C technology XXX is unclear or troublesome", etc. Finally, I don't think it is surprising that the people who have financed XML Schema's development should be keen to use it (uddi.org seems to have many of the same key players as are in the W3C). I don't think anyone is claiming that the recent XML Schema drafts are useless. But that does not really speak about whether XML Schemas attempts "too much": that is an unresolvable question because XML has expanded to be more than just the simple data-interchange format. Now it is a Nutty Professor II -style family of technologies that are being used to model/process the databases as well as the reports. (I think that was a key issue, actually: should XML Schemas have limited itself to only small documents on single topics {i.e., reports) or must it provide enough metadata decorations of the infoset to provide XQuery with the basis it needs? Indeed, is XQuery really XML at all, if it is concerned with querying of large databases rather than data transfer? A document can be a database, but in moving to support databases, do we lose the plot and the focus on interchange? It is a pity that this issue has never really, to my knowledge, been discussed much publically--it has just sort-of happened to XML, and reactions like SML are hardly surprising.) Finally, I should point out that it is perfectly possible to derive your own restricted schema language based on XML Schemas, and adopt that in your organization, if full XML Schemas is too big. This is no different from adopting a particular profile of XML (as XML itself is a profile of SGML). You could, for example, decide that you will only make use of structural features that have direct equivalents in DTDs. Or not to derive your own datatypes. You could even make up your own tools for these--such tools would not be conforming XML Schema tools, but they might be useful. Just because XML Schemas provides a feature does not mean one has to use it! Rick Jelliffe
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