An XML Schema describes the structure of an XML document. The XML Schema language is also referred to as XML Schema Definition (XSD).

XML documents can have a reference to a DTD or to an XML Schema.

The element is the root element of every XML Schema.

XML Schemas define the elements of your XML files. A simple element is an XML element that contains only text. It cannot contain any other elements or attributes.

All attributes are declared as simple types.

Restrictions are used to define acceptable values for XML elements or attributes. Restrictions on XML elements are called facets.

A complex element contains other elements and/or attributes.

An empty complex element cannot have contents, only attributes.

An "elements-only" complex type contains an element that contains only other elements.

A complex text-only element can contain text and attributes.

A mixed complex type element can contain attributes, elements, and text.

We can control HOW elements are to be used in documents with indicators.

The element enables us to extend the XML document with elements not specified by the schema!

The element enables us to extend the XML document with attributes not specified by the schema!

With XML Schemas, one element can substitute another element.