XML: Visual QuickStart Guide, Second Edition

Chapter 9. XML Schema Basics

The specifications for XML include the syntax for a schema language: A way to define what a valid XML document could contain. This language, known as a DTD (Document Type Definition), enables users to define elements, attributes, and their relationships for any application of XML needed (see Part 3).

In 2001, the W3C developed a new schema language to address many of the shortcomings of DTD (see page 110). This schema language was named XML Schema, which is admittedly confusing because DTDs are a type of XML schema (lower case “s”). Even still, it’s most often called XML Schema, though it is occasionally called XML Schema Definition (XSD). And now, with version 1.1 of the language, it is known as XML Schema Definition ...