XML Schema Complete Reference, The

Chapter 13. Identity Constraints

IN THIS CHAPTER

13.1 Identity Constraint Example

13.2 Concepts and Observations

13.3 The unique Element

13.4 The key Element

13.5 The keyref Element

13.6 The selector Element

13.7 The field Element

Chapter 1 defines an XML validator as an XML parser layer that validates an XML instance against an XML schema. An XML validator is effectively the front end of a compiler. Specifically, a “vanilla” XML parser understands XML lexical tokens and parses against a simple XML grammar. Most of the features of a DTD place further constraints on the grammar. The newer XML Schema provides an even more complete grammar definition.

When a compiler has finished parsing, the next step is typically semantic validation. Semantic ...