RE: [xml-dev] Non-schema approach to web service design: comments?

["Mark Seaborne" <MSeaborne@origoservices.com>]

> I see how this would be vastly easier in Schematron, or 
> another schema language that allows co-occurrence 
> constraints?  I should have instantly thought of that as the 
> most commonly discussed reason why real-world format 
> constraints can't be expressed in XSD.
> 
> Strictly speaking, Schematron is independent of / 
> complementary to XSD, however.  It seems like it would be 
> easier to figure out how to get them to work usefully 
> together than start the schema wars over again.

This is an approach that we have been investigating recently. I work for a vertical industry standards body that develops WXS schemas for the UK life and pensions industry (http://www.origostandards.com). We have long recognised the limits of WXS expressive power, so we have begun experimenting with the combination of Schematron and WXS. 

In the end we decided to expose our first Schematron schema via XForms. XForms allows the definition of XPath based constraints like Schematron (so we can replicate the assertions we define), and most usefully, it defines how these be combined with WXS schema types. Obviously XForms also allows you to define a UI if you want one, so we have started development of a form that presents an instance validity report to a user (see http://www.origostandards.com/XForms/InstanceValidator/). 

It is at a very early stage of development, so the form is rather primitive and I think our Schematron schema is a bit dodgy, but there is enough to demonstrate the power of combining WXS/Schematron/XForms. Unfortunately, due to time constraints, we have only been able to test the form with the Novell XForms processor (link from above site), but it should work with others once the CSS has been tweaked.

All the best

Mark Seaborne
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