Validation of complex content

[Edwin Dankert <edankert@gmail.com>]

Hello,

I hope you can guide me in the best way to proceed with this validation issue.

I have a XML structure with most of the nodes representing simple
data, like names, references and numeric values.

<person>
  <name>John<name>
  <salary>1000<salary>
</person>

However some of the numeric nodes can not only represent the data as
simple numeric values, they can also be specified as an expression and
point to other items in the document.

<person xmlns="x">
  <name>John<name>
  <salary>100000/$no-of-employees}<salary>
</person>

The expression language is quite complex and cannot be represented by
a regular-expression. The syntax is however specified using EBNF and
only the syntax needs to be validated.

A XML Schema for this exists:

<schema>
  <element name="person">
    <sequence>
      <element name="name" type="Name">
      <element name="salary" type="string">
    </sequence>
  </element>
<schema>

The goal is to have a standalone tool which can validate using the
more simple constraints specified by the schema and also validate the
values which contain the expression language.

My preferred solution would involve validating the expression value
syntax directly from the EBNF using standard XML technologies but
don't believe this is currently an option.

My questions now is: what would be the best way to validate these
values in your opinion or how was this solved in any of your previous
projects? (Note: The validator tool-set already includes Java, NVDL,
XSLT 2.0, XML Schema 1.0.)

Any suggestions are very welcome.

Thanks in advance,
Edwin