Editing XML schema (section)

=== Schematron ===
{{main|Schematron}}

Schematron is a fairly unusual schema language. Unlike the main three, it defines an XML file's syntax as a list of [[XPath]]-based rules. If the document passes these rules, then it is valid.

==== Advantages ====

Because of its rule-based nature, Schematron's specificity is very strong. It can require that the content of an element be controlled by one of its siblings. It can also request or require that the root element, regardless of what element that happens to be, have specific attributes. It can even specify required relationships between multiple XML files.

==== Disadvantages ====

While Schematron is good at relational constructs, its ability to specify the basic structure of a document, that is, which elements can go where, results in a very verbose schema.

The typical way to solve this is to combine Schematron with RELAX NG or W3C XML Schema. There are several schema processors available for both languages that support this combined form. This allows Schematron rules to specify additional constraints to the structure defined by W3C XML Schema or RELAX NG.

==== Tool Support ====

Schematron's reference implementation is actually an [[XSLT]] transformation that transforms the Schematron document into an XSLT that validates the XML file. As such, Schematron's potential toolset is any XSLT processor, though [[libxml2]] provides an implementation that does not require XSLT. [[Sun Microsystems]]'s Multiple Schema Validator for [[Java (programming language)|Java]] has an add-on that allows it to validate RELAX NG schemas that have embedded Schematron rules.