Important design points

Not just datatypes but a type system
- Type derivation by restriction, extension
- Type substitution rules
Framed in terms of infoset not the character stream: input and results
All schema components first class (web) objects
Extensible annotations on all schema components
Layered interoperability architecture:
1. Conceptual level
2. Transfer syntax level
3. Web interoperability level
Validity is not a binary choice