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Manipulating Control Elements: a Flexible Mechanism for Cooperative Information Systems Proofs of Lemmas and Theorems

Cooperative information systems (CISs) are information systems with data dependencies and interoperability relationships. The paradigm for such systems involves large numbers of information systems distributed over large, complex com-puter/communication networks. Due to unreliable network technologies, and the possible autonomous decisions of availability of each information system, CISs should be exible enough to maintain a reasonable level of operation. In this paper we introduce control elements as a tool for modeling the relationships among CISs. A control element combines a deenition of a set of CISs' global behavior with an executable data structure for cooperation among them. Manipulating control elements using local transformations increases the exibility of these systems by allowing multiple paths for receiving data and activating operations. We provide two techniques for manipulating control elements, namely the substitute method and the phantom node method. Using these techniques, CISs can change the level of interaction among themselves, and increase parallelism. The paper presents a complexity analysis showing the low cost of local transformation using these techniques. Control elements are implemented as part of the CoopWARE environment for supporting the cooperation among information systems.