MODELING COLLABORATIVE BEHAVIOR USING COOPERATION CONTRACTS

Several objects exhibit collaborative behavior if they act together in answering a message they have received jointly. Collaborative behavio r is defined by cooperation contracts which are established between se veral object classes and which declare a set of cooperative methods. A cooperative method is invoked by a cooperative message sent to a tupl e of instances, one for each object class in the cooperation contract. This extends the traditional message passing paradigm which requires the receiver of a message to be a single object only. Cooperation cont racts offer several benefits for behavior modeling in object-oriented database design. Behavior provided by several object classes in concer t needs not be dispersed and can be defined in a single place. Therefo re, behavior designs become symmetric, more maintainable and better ex tensible. Cooperation contracts can easily be made available as benefi cial modeling constructs in existing object-oriented database manageme nt systems by adding a few classes. This paper presents such an extens ion based on the commercial object-oriented database management system GemStone.