Sunday, May 17, 2009

Xerces-J XSD 1.1 assertions and PsychoPath XPath 2.0 processor update

I recently contributed few patches to the Eclipse PsychoPath XPath 2.0 engine, to support Schema aware XPath (2.0) expressions. These patches would enhance Schema aware support in PsychoPath XPath2 engine, for element and attribute nodes, for the XML Schema primitive types.

These enhancements in PsychoPath engine would make XPath expressions like following possible, to be evaluated by PsychoPath engine:

person/@dob eq xs:date('2006-12-10') // if dob is an attribute, and of schema type xs:date

person/dob eq xs:date('2006-12-10') // if dob is an element, and of schema type xs:date

@max ge @min // this would work if 'max' and 'min' have say schema types, xs:int

The patch in my local environment already exhibits these improvements. As promised by Dave Carver (the PsychoPath engine project lead), users would likely get these improvements in Eclipse WTP (Web Tools Project) 3.2.
2009-05-24: These changes are now committed to the Eclipse CVS server, and the improvements are flagged to be delivered in Eclipse WTP 3.2 M1, which should be quite sooner. Thanks to Dave Carver for testing all my patches, and committing them to the server.

PsychoPath engine already has a framework (thanks to Andrea Bittau and his team) for supporting Schema awareness (based on the Xerces-J XSD schema model). I just added in small pieces of code in attribute and element node implementations (particularly, improving the "typed value" of attribute and element nodes for built in XSD schema types), to enhance schema aware support.

I think, we are gradually moving to a more mature schema aware support in PsychoPath.

I'm also using these new PsychoPath processor capabilities, to implement schema aware XPath 2.0 evaluations in Xerces-J XSD assertions support.

I'm currently working on to construct a typed XPath data model instance, for XSD 1.1 assertions evaluations. Having this capability, would allow users to write XPath expressions like, following:

@max ge @min


person/@dob eq xs:date('2006-12-10')

In the absence of this (i.e, typed XDM nodes), currently users have to make explicit cast operations, like following:

xs:int(@max) ge xs:int(@min)


xs:date(person/@dob) eq xs:date('2006-12-10')

The XML Schema 1.1 assertions spec recommends a typed XDM instance.

We hope to provide this capability within Xerces-J, inline with the XML Schema 1.1 assertions specification.

2009-05-23: These improvements are now implemented, and I've submitted the code improvements to the Apache Xerces-J JIRA server. I'm hoping, we'll have these improvements committed on the Xerces-J SVN server some time soon.

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