GOM: A Strongly Typed Persistent Object Model With Polymorphism

Alfons Kemper, Guido Moerkotte, Hans-Dirk Walter, Andreas Zachmann

Abstract: In this paper the persistent object model GOM is described. GOM is an object-oriented data model that provides the most essential object features in a “lean” and coherent syntactical framework. These features include: object identity, object instantiation, subtyping and inheritance, operation refinement, dynamic (late) binding. One of the main goals in the design of GOM was type safety. In order to achieve this we developed a strongly typed language that enables the verification of type safety at compile time. It is shown in this paper how commonly encountered “traps” for strong typing are avoided in GOM by specifying a very clean subtyping semantics on the basis of substitutability and type signatures.