XML Schema (XSD)
XSD (XML Schema Definition) defines the types, elements, attributes, and constraints of XML documents in XML syntax; it is the modern replacement for DTD.
Purpose
To provide rich type-system and structural validation for XML documents, supporting namespaces and type inheritance.
Mechanism
<xs:element>, <xs:complexType>, and <xs:simpleType> define elements and types. <xs:restriction> constrains value ranges, and <xs:sequence>/<xs:choice> define content models. Namespaces and type derivation are supported.
Use cases
- XML web service contracts
- SOAP message validation
- Data exchange standards