XSD Validation

Estimated study time: 12 minutes.

Validation is the process of checking whether an XML document conforms to the rules defined in its XSD schema — correct elements, correct types, correct order, and correct constraints.

How Validation Works

A parser reads both the XML document and its referenced XSD, then checks the document against the schema's rules. If anything doesn't match — a missing required element, wrong data type, invalid attribute value — validation fails with a specific error.

Adding Constraints with Facets

<xs:simpleType name="seatCount">
  <xs:restriction base="xs:integer">
    <xs:minInclusive value="1"/>
    <xs:maxInclusive value="60"/>
  </xs:restriction>
</xs:simpleType>

This restricts a numeric value to a specific range. Other common facets include pattern (regular expression matching), minLength/maxLength, and enumeration.

Pattern Example

<xs:simpleType name="courseId">
  <xs:restriction base="xs:string">
    <xs:pattern value="[A-Z]{2}-[0-9]{3}"/>
  </xs:restriction>
</xs:simpleType>

This forces values like DA-101 to match the pattern, rejecting anything that doesn't fit.

Why Validation Matters

• Catches bad data before it reaches downstream systems or databases.
• Provides a clear, shared contract between systems exchanging XML.
• Reduces the need for manual data-checking code in your application.