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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] multiple schemas, annotations
 Tim Ewald gave an excellent presentation at the Applied XML conference last month on his use of W3C XML Schema in MSDN publishing processes. There were a lot of interesting facets, but one that's particularly stuck with me is his discussion of multiple levels of schema validation, each with different schemas. His system uses schemas in a number of ways - mostly as gateways - but some of those gates are wider than others. Documents have to pass only very basic validation on initial submission but the requirements get stricter as documents are sorted and get closer to their final destination. If I remember his system right, some of that reflects document evolution while in the system while some of it reflects a growing awareness of what the document should look like over the course of categorization. In general, though, this multi-schema approach seems like an opportunity to create more flexible piplelines than what I'll call the schema-as-contract model, in which all documents going through a process are expected to conform to a single schema. It reflects local processing needs and provides support for documents to evolve over time rather than arrive full-grown. It may not be for everyone, but it's something I expect to see happening more often, even in more data-oriented situations. This approach also raises interesting questions about schema languages which annotate documents with additional information, typically attributes - notably DTDs and WXS. While I have doubts about the practice generally, this kind of annotation can be very useful for some kinds of transformative interpretation, notably architectural forms. Having multiple schemas with different attribute annotations can make it a lot easier, for instance, to convert a single data format using a particular set of identifiers into a range of other formats using a relatively generic transformation. Annotative approaches, freed from "there can be only one schema", seem to be powerful tools for reducing the cost of making multiple vocabularies interoperate. There is still, of course, a cost, but creating annotations seems generally an easier thing for many people to do than creating transformations. It also suggests to me that it might be wise to create an annotation engine separate from schema validation. RELAX NG's core lacks annotation facilities by design, and all of the schema annotation approaches come with their own baggage. Perhaps the DSDL folks are already discussing this. -- Simon St.Laurent Ring around the content, a pocket full of brackets Errors, errors, all fall down! http://simonstl.com -- http://monasticxml.org 
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