TYPE DERIVATION USING THE PROJECTION OPERATION

We present techniques for deriving types from existing object-oriented types using the relational algebraic projection operation and for inf erring the methods that are applicable to these types. Such type deriv ation occurs, for example, as a result of defining algebraic views ove r object types. We refactor the type hierarchy and place the derived t ypes in the type hierarchy in such a way that the state and behavior o f existing types remain exactly as before. Our results have applicabil ity to relational databases extended with object-oriented type systems and to object-oriented systems that support algebraic operations.