Question

For example,

Xml document:

<some_document>
 <elements>
  <element>1</element>
  <element>2</element>
  <element>3</element>
 </elements>
 <sum>6</sum>
<some_document>

Rules(in some form, probably in xml), according to schema of given document:

Sum of all <element> fields must match the value in <sum> field

Result:
Is document valid, according to rules specified or not?(in xml form too, probably)

So, I need a library that implements given functionality or at least points to dig in for writing one by myself. Language does not matter.

Answer 1

Schematron would probably be a good solution.

Schematron is an ISO standard and provides a way of encoding business rules, restrictions and validation that is not possible in XML Schema. The rules are comiled into XSLT and can run in any environment that can invoke XSLT transformations.

The Schematron differs in basic
concept from other schema languages in
that it not based on grammars but on
finding tree patterns in the parsed
document. This approach allows many
kinds of structures to be represented
which are inconvenient and difficult
in grammar-based schema languages. If
you know XPath or the XSLT expression
language, you can start to use The
Schematron immediately.