This article has only touched on the most commonly used features of XML Schema. XML Schema is rich with other functionality that can be used in more complex cases. This functionality includes the following:
Annotations can be defined to provide documentation or application information for any schema component.
Type Derivation allows simple and complex types to be derived from other types.
Reusable Groups can be defined to name fragments of content models and/or groups of attributes that are used in many types.
Identity Constraints allow you to enforce uniqueness constraints and referential integrity in your XML documents.
Substitution Groups are a way to designate elements as substitutes for other elements in content models, making those content models more flexible and extensible.
Redefinition is a way to reuse schema documents while making modest changes to the components in them.
However, you are not required to use (or even understand!) all these features to create useful schemas. Choose only the subset you need in order to get the most benefit from W3C XML Schema.