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XML Hacks by Michael Fitzgerald

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Check the Integrity of a W3C Schema

Use the xni.XMLGrammarBuilder class from Xerces to do some extra checking on your schemas.

Whether you create a W3C XSD Schema with the same tools you use to create other XML documents or use a specialized schema-generation tool to create one, parsing it against the schema in the Schema for Schemas appendix of the W3C Schema recommendation (http://www.w3.org/TR/xmlschema-1/#normative-schemaSchema) may alert you to some problems, such as whether you mistyped the name of a schema definition element or put one schema definition element inside of another where it doesn’t belong. There are other potential errors that this won’t catch, though; for example, what if your maxOccurs value for one element is less than the minOccurs value for the same element?

The xni.XMLGrammarBuilder class manages this multidocument validation by creating a compiled version of that schema in memory and then re-using that compiled version for each instance document passed to it. Like any compiler, it makes various integrity checks as it compiles. If you’re developing an XSD schema, this round of checks can help you before you’ve created your first document that conforms to that schema.

Imagine that you just drafted a schema, badschema.xsd, which has the following problems:

  • In the content model for the order element, the itemNum element has a maxOccurs value of 1 and a minOccurs value of 4. If the value must be greater than or equal to 4 or and less than or equal to 1, that ...

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