You can create custom user-defined data types using the <simpleType> definition:
<simpleType name="name of the simpleType"
final="#all or list or union or restriction">
To declare a <simpleType>, you must always base your declaration on an existing data type.
The existing data type may be a built-in XML Schema data type or a custom datatype.
<simpleType>definitions are often called derived types.
There are three primary derived types:
Restriction types
List types
Union types