abstract types

I'm creating a number of base data types. I had originally planned on  
just using simpleType as shown below. Looking at the various docs, it  
looks as though I can't make a simpleType 'abstract'. I want to mark  
the base types as abstract in order to indicate that derived types  
must be created for use.

Am I correct that I'll need to convert the below to a complexType?



     <!--BOOLEAN type -->
     <xs:simpleType name="booleantype">
         <xs:restriction base="xs:boolean"/>
     </xs:simpleType>

Just wanted to verify this before I start reworking all of my base  
types.


-David