XML Schema: Four requirements
 
  - Reconstruct DTD functionality using XML:
   
  
- Integrate Namespaces:
   
    - Modular schemas for modular document types.
 
- Provide a usable inventory of basic datatypes.
   
    - For elements as well as attributes.
 
- Support object-oriented design:
   
    - Kind-of as well as part-of.