#5 Simple Schema Implementation

[Kal Ahmed]

Implement some simple form of topic map schema. Perhaps
based on the Ontopia topic map schema language ?
Whatever schema language is chosen, it should be
expressed in a topic map. The implementation should allow:

1) Runtime validation - programmer can call
validate(tm, schemaTM) and get a list of schema
violations in tm.

2) Runtime change veto - programmer can attach a
vetoable change listener to the topic map which will
ensure that all changes which violate the schema raise
a PropertyVetoException.