1 Object-oriented databases: systems and standards

Since the mid-eighties when Gemstone was introduced as the first object-oriented database management system (ODBMS), a dozen other commercial ODBMSs have joined the fierce competition in the market. Although we call them all ODBMSs, they differ in their system concepts and data management standards. Below, I discuss the past evolution and future prospects of those ODBMSs. Evolution of systems There have been three approaches to building an ODBMS: extending an object-oriented programming language (OOPL), extending a relational DBMS, and starting from the ground up. The first approach realizes an ODBMS by adding to an OOPL persistent storage for multiple concurrent accesses with transaction support. This extension has the advantage of reusing the type system of a programming language as a data model and thus achieves a seamless integration between programming language and database manipulation language. This approach has become the most popular in the commercial world so far and is represented by commercial ODBMSs such as ObjectStore, Versant, Objectivity, and O2. In the second, extended relational approach, an ODBMS is built by enhancing an existin