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 inferring the methods that are applicable to these types. Such type derivation occurs, for example, as a result of defining algebraic views over object types. We refactor the type hierarchy and place the derived types in the type hierarchy in such a way that the state and behavior of existing types remain exactly as before. Our results have applicability to relational databases extended with object-oriented type systems and to object-oriented systems that support algebraic operations. © 1994.