XML - XML Validator

 What is XML?

XML (eXtensible Markup Language) is a language used to store and transport data. It is readable by both humans and machines.

 Example of a simple XML file:

<student>
  <name>John</name>
  <age>20</age>
  <course>Computer Science</course>
</student>

 

What is an XML Validator?

An XML Validator is a tool or program that checks if your XML file is correct and follows the rules.

There are two types of validation:

 

 1. Well-Formed XML

This means your XML follows basic syntax rules.

✔️ Rules for well-formed XML:

  • Must have one root element

  • All tags must be properly opened and closed

  • Tags must be nested correctly

  • Attribute values must be in quotes

 Example of not well-formed XML:

<student>
  <name>John</name>
  <age>20<age> <!-- Closing tag is wrong -->
</student>

A well-formed XML can still be invalid if it doesn’t follow a defined structure (like a grammar).

 

 2. Valid XML

This means your XML is well-formed AND follows the structure rules defined in:

  • DTD (Document Type Definition)

  • XSD (XML Schema Definition)

These define:

  • What tags are allowed

  • The order of tags

  • What data types the values should have (for example: age must be a number)

 

DTD (Document Type Definition)

Defines the structure of your XML using a simpler syntax.