Correctly typing objects through subtyping and type interference

In this paper we present a type system with strong typing and static type checking that is not yet well supported in most existing object-oriented database systems. Using a partial ordering defined on type structures and on methods associated to types, we define a subtyping rule for correctly structuring the inheritance hierarchy of the types. Based on the subtyping, a number of type inference rules are defined. They can be used by the type system to statically determine the types of the query results and whether a given application program is type correct.