XML — Validation

Well-Formed vs Valid

Well-formed: Follows XML syntax rules
Valid: Conforms to a DTD or Schema

DTD (Document Type Definition)

<?xml version="1.0"?>
<!DOCTYPE note [
    <!ELEMENT note (to, from, heading, body)>
    <!ELEMENT to (#PCDATA)>
    <!ELEMENT from (#PCDATA)>
    <!ELEMENT heading (#PCDATA)>
    <!ELEMENT body (#PCDATA)>
]>
<note>
    <to>Tove</to>
    <from>Jani</from>
    <heading>Reminder</heading>
    <body>Don't forget me!</body>
</note>

XML Schema (XSD)

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="note">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="to" type="xs:string"/>
                <xs:element name="from" type="xs:string"/>
                <xs:element name="heading" type="xs:string"/>
                <xs:element name="body" type="xs:string"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>

DTD vs Schema

Feature	DTD	XSD
Syntax	Non-XML	XML
Data types	Limited	Full support
Namespace	No	Yes
Complexity	Simple	More complex

Referencing a Schema

<?xml version="1.0"?>
<note xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="note.xsd">
    <to>Tove</to>
</note>

Mini Practice

Create a DTD for a simple document
Create an XML Schema
Validate XML against both
Add constraints with Schema types

Up Next

Continue with Tree — understanding XML tree structure.

Frequently Asked Questions about Validation

What is Validation in XML?

Validation is a fundamental concept in XML. This lesson explains it step by step with clear examples, making it easy for beginners to understand.

How do I learn Validation?

Start by reading the explanation above, then try the code examples. Practice by modifying the examples and experimenting with different values. Hands-on practice is the best way to learn Validation.

Why is Validation important in XML?

Validation is essential for XML development. Understanding this concept will help you write better code and solve real-world problems more effectively.