Uniqueness and Document-Oriented Issues
- ID, IDREF, and IDREFS Like XML 1.0 DTDs, XML Schemas provide the ID type for identifiers that must be unique within a document, IDREF for values that must match one of those identifiers, and IDREFS for cases where more than one value might be referenced.
- Keys and keyrefs XML schemas add the concept of keys to the ID/IDREF mix, using XPath information to add requirements to documents. (In some ways this feels like schematron. These tools allow schema developers to add requirements to a document on a for-each key this corresponding keyref basis.
- Unique The
unique element allows schema designers to create selectors with a subset of XPath identifying a particular region in a document and then specify a particular field that must be unique within that region or the document as a whole.
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Copyright 2000 Simon St.Laurent