MDM: An Object-Oriented Data Model

This paper describes MDM, an object-oriented data model that supports instance-level evolution and associative queries. The MDM type system, based on abstract types and conformity, allows flexibility in defining applications and interacts well with the query facility. The query algebra consists of a small set of simple operators; many other useful operators can be defined through composition. MDM defines only a primitive notion of object equivalence, although the algebra includes an operator that allows user-defined equivalence relations to direct the grouping of objects in a multiset.