Namespaces and schema references
The Namespaces standard (see Chapter 10) can rarely be ignored when using XML Schemas. Namespaces must be considered both when using certain techniques within the schema model (the impact of namespaces on references to data types has already been demonstrated), and also when validating documents that use namespaces.
Schema document namespaces
The productivity techniques described later rely upon the ability of a schema author to create new data types that can be shared across several element or attribute definitions. In order to avoid confusing custom data types with built-in types, it is necessary to use two namespaces. When the XML documents to be validated do not use namespaces, a namespace prefix must not ...