XSD

XSD (XML Schema Definition) is the W3C-standard language for defining XML document structure, describing elements, attributes, and type constraints in XML syntax.

Purpose

To provide strict validation of XML documents, defining element hierarchy, types, and constraints.

Mechanism

It declares in XML syntax: element defines elements, complexType defines structures, and simpleType defines constraints (e.g., enumeration, regex). It supports namespaces, type inheritance, and substitution groups. Validators (e.g., xmllint) check XML documents against it.

Use cases

SOAP WSDL type definitions
Enterprise data exchange schemas
Government/financial XML standards
Document validation

Examples

Input

<xs:element name="age" type="xs:int"/>

Output

The age element must be an integer

A type constraint

Common errors

An overly complex schema becomes hard to maintain: Generate it with tools or consider JSON Schema

Related terms

XML (Extensible Markup Language) is the W3C-standard markup language describing data with a tag tree, supporting namespaces, schema validation, and style transformation.

A DTD (Document Type Definition) is the structure-definition mechanism of XML 1.0; it is simpler than XSD but limited, and is written in a special (non-XML) syntax.

JSON Schema is a vocabulary for describing the structure of JSON documents, defining types, constraints, and validation rules; it is the schema standard for JSON.

References