Introduction to XML Schemas

From http://www.w3schools.com (Copyright Refsnes Data)

# Introduction to XML Schema

XML Schema is an XML-based alternative to DTD.

An XML schema describes the structure of an XML document.

The XML Schema language is also referred to as XML Schema Definition (XSD).

## What You Should Already Know

Before you continue you should have a basic understanding of the following:

- HTML / XHTML
- XML and XML Namespaces
- A basic understanding of DTD

If you want to study these subjects first, find the tutorials on our Home page.

## What is an XML Schema?

The purpose of an XML Schema is to define the legal building blocks of an XML document, just like a DTD.

An XML Schema:

- defines elements that can appear in a document
- defines attributes that can appear in a document
- defines which elements are child elements
- defines the order of child elements
- defines the number of child elements
- defines whether an element is empty or can include text
- defines data types for elements and attributes
- defines default and fixed values for elements and attributes

## XML Schemas are the Successors of DTDs

We think that very soon XML Schemas will be used in most Web applications as a replacement for DTDs. Here are some reasons:

- XML Schemas are extensible to future additions
- XML Schemas are richer and more powerful than DTDs
- XML Schemas are written in XML
- XML Schemas support data types
- XML Schemas support namespaces

## XML Schema is a W3C Recommendation

XML Schema became a W3C Recommendation 02. May 2001.

You can read more about the XML Schema standard in our W3C tutorial.

From http://www.w3schools.com (Copyright Refsnes Data)