You can derive new simple types from existing types.
An xsd:simpleType element defines the subtype
The name attribute
of xsd:simpleType assigns a name to the new type,
by which it can be referred to in xsd:element
type attributes.
An xsd:restriction child element derives by restricting
the legal values of the base type
An xsd:list child element derives a type as a
white space separated list of base type instances
An xsd:union child element derives by
combining legal values from multiple base types