Use in Schema Languages
XPath is increasingly used to express constraints in schema languages for XML.
- The (now ISO standard) schema language Schematron pioneered the approach.
- A streaming subset of XPath is used in W3C XML Schema 1.0 for expressing uniqueness and key constraints. In XSD 1.1, the use of XPath is extended to support conditional type assignment based on attribute values, and to allow arbitrary boolean assertions to be evaluated against the content of elements.
- XForms uses XPath to bind types to values.
- The approach has even found use in non-XML applications, such as the constraint language for Java called PMD: the Java is converted to a DOM-like parse tree, then XPaths rules are defined over the tree.
Read more about this topic: XPath
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