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   Re: [xml-dev] multiple schemas, annotations

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Simon St.Laurent wrote:

> 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.

New jargon opportunity - content firewall.

> 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.

A similar effect can be achieved with a pipeline of XPath filters. 
Consider that an XPath assertion a good unit testing technique for 
XML generation, if you didn't have a schema to hand.

Another plus is that you can mix amd match schemas from different 
languages and adminstrations. Nicely organic, given that One True 
Domain Models don't always work out in practice.

> 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.

What's useful about this approach is that you can pepper a document 
with attributes without mucking about with document structure or 
leaving <any/> slots all over the place. Attributes are easy to ignore.

> 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.

I've always liked the XLink idiom for RDF.

Bill de hÓra

Technical Architect


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