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Modeling Collaborative Behavior Using Cooperation Contracts

Authors: M. Schrefl, G. Kappel, P. Lang
Technical Report: TR9602 (October, 1996)
Report number: 96.02
Resources: Copy  (In order to obtain the copy please send an email with subject  TR9602  to


Several objects exhibit collaborative behavior if they act together in answering a message they have received jointly. Collaborative behavior is defined by cooperation contracts which are established between several object classes and which declare a set of cooperative methods. A cooperative method is invoked by a cooperative message sent to a tuple 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 contracts offer several benefits for behavior modeling in object-oriented database design. Behavior provided by several object classes in concert needs not be dispersed and can be defined in a single place. Therefore, behavior designs become symmetric, better maintainable and better extensible.

Cooperation contracts can easily be made available as beneficial modeling construct in existing object-oriented database management systems by adding a few classes. This paper presents such an extension based on the commercial object-oriented database management system GemStone.

Keywords:multiple polymorphism, collaborative behavior modeling, cooperation contracts, object-oriented database design