Valid XML Documents
An XML document can be valid. This means that there exists a set of rules describing what type of content is allowed within a document. XML defines two very different mechanisms for defining such a set of rules:
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Document Type Declaration (DTD) : a text file (or set of commands embedded within an XML document) that specify the rules for an XML document.
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XML Schema: a document that describes the rules for an XML document. Schemas are themselves written in XML.
Caché provides support for validating documents using either DTDs or XML Schemas.