Cooperation Contracts

In this paper we introduce the concept of cooperative message handling, in which several objects act together in answering a message they have received jointly. cooperative message handling extends the traditional message passing paradigm which requires the receiver of a message to be a single object only. Cooperative messages are defined with cooperation contracts which are established between several object types. A cooperative message is sent to a tuple of instances, one for each object type in the cooperation contract. We show that cooperation contracts offer new benefits for behavior modeling in object-oriented database design. Behavior which is provided by several object types in concert needs not be dispersed and can be defined in a single place. Furthermore, behavior designs become symmetric, better maintainable and better extensible.