Object-oriented database servers are beginning to appear on the commercial market in response to a demand by application developers for increased modeling power in database systems. Before these new servers can enhance the productivity of application designers, systems designers must provide simple interfaces to them from both procedural and object-oriented languages. This paper first describes a successful interface between an object server and two procedural languages (C and Pascal). Because C and Pascal do not support the object-oriented paradigm application, designers using these languages must deal with database objects in less than natural ways. Fortunately, workstations supporting object-oriented languages have the potential for interacting with database objects in a much more integrated manner. To integrate these object-oriented workstations with an object server, we provide a design framework based on the notion of workstation agent objects representing principal objects in the database. We distinguish two types of agents: proxies , which forward most messages to the principal objects, and deputies , which can cache state for their principal and act with more autonomy. The interaction of cache, transaction, and message management strategies makes the implementation of deputies a nontrivial problem. The agent metaphor is being used currently to integrate an object server with a Smalltalk-8O™ workstation.

We describe the results of developing the GemStone object-oriented database server, which supports a model of objects similar to that of Smalltalk-80. We begin with a summary of the goals and requirements for the system: an extensible data model that captures behavioral semantics, no artificial bounds on the number or size of database objects, database amenities (concurrency, transactions, recovery, associative access, authorization) and an interactive development environment. Object-oriented languages, Smalltalk in particular, answer some of these requirements. We discuss satisfying the remaining requirements in an object oriented context, and report briefly on the status of the development efforts. This paper is directed at an audience familiar with object-oriented languages and their implementation, but perhaps unacquainted with the difficulties and techniques of database system development. It updates the original report on the project [CM], and expands upon a more recent article [MDP].