XSD Tutorials - Herong's Tutorial Examples - v5.23, by Herong Yang
What Are Identity-Constraints?
This section describes 3 types of identity constraints supported by XSD: 'unique', 'key' and 'keyref' identity constraints. They are very similar to concepts of UNIQUE, PRIMARY KEY and FOREIGN KEY constraints on multiple columns in a database table.
XSD offers 3 types of identity constraints:
1. "unique" Identity Constraint - A repeating set of attributes or elements are specified as a unique identity. Their values must be unique, if exist. "unique" identity constraint is very similar to the concept of UNIQUE constraint on multiple columns in a database table.
2. "key" Identity Constraint - A repeating set of attributes or elements are specified as a key identity. Their values must exist and be unique. "key" identity constraint is very similar to the concept of PRIMARY KEY constraint on multiple columns in a database table.
3. "keyref" Identity Constraint - A repeating set of attributes or elements are specified as a key reference identity. Their values must exist and refer to existing values another key identity. "keyref" identity constraint is very similar to the concept of FOREIGN KEY constraint on multiple columns in a database table.
A good example of a "unique" identity constraint is the "id" attribute used in XHTML documents. It should have unique values within the document, if used.
Table of Contents
XML Editor and Schema Processor - XMLPad
Java API for XML Processing - JAXP
JAXP - XML Schema (XSD) Validation
Xerces2 Java Parser - Java API of XML Parsers
Introduction of XSD Built-in Datatypes
"string" and Its Derived Datatypes
"decimal" and Its Derived Datatypes
"dateTime" and Its Related Datatypes
Miscellaneous Built-in Datatypes
Facets, Constraining Facets and Restriction Datatypes
"simpleType" - Defining Your Own Simple Datatypes
►Identity-Constraints: unique, key and keyref
►What Are Identity-Constraints?
What Is "unique" Identity-Constraint?
What Is "key" Identity-Constraint?
What Is "keyref" Identity-Constraint?
"keyref" Identity-Constraint XSD Example
Identity-Constraint with Multiple Fields
Assertion as Custom Validation Rules
XML Schema Location and Namespace in XML Documents
Overriding Element Types in XML Documents