Using XML with Legacy Business Applications

Extending and Restricting Simple Types

Simple types can be either extended or restricted. Again, we don't change the content model of a simple type since simple types always have a simple content model, that is, no child Elements may be defined. We extend the simple type into a complex type by adding one or more Attributes. We restrict a simple type by using one of its constraining facets that reduces the range of allowable values. Extension of a simple type is done by using the schema language xs:extension Element. We'll see it used in the Attribute Declarations subsection below. Restriction is done by using the schema language xs:restriction Element. We'll see examples of this next. Both extension and restriction must specify a “base,” that ...