Object‐Oriented Protocol Hierarchies for Distributed Workflow Systems
Peter C. Lockemann, Hans‐Dirk Walter · Theory and Practice of Object Systems · 1995
Modern information systems will increasingly have to support the cooperation between more or less independent partners that are distributed across local or global networks. Since the partners can naturally be modeled by objects, means must be provided that permit to model the cooperation among objects. In this paper we propose an extended object model which allows the explicit definition of dynamic relationships between objects. The new construct, called alliances, can be viewed as a protocol that materializes and enforces the cooperation of an arbitrary number of objects by relying on a set of communication rules. The rule‐based approach allows to specify cooperation protocols which circumscribe a space of possible cooperations. In other words, cooperation protocols restrict cooperation among objects to the minimum extent needed to leave the objects enough leeway for spontaneous reactions while still guaranteeing that the constraints inherent in a cooperation on a common task are being met. Workflows are specifications of cooperative applications. We demonstrate how alliances can be used as an implementation model for distributed workflow systems, which is superior to a pure object‐based implementation. This suggests that alliances are a lower‐level, more implementation‐oriented support structure for workflows. In particular, it should be possible to derive the cooperation constraints of an alliance from higher‐level workflow specifications which model business processes. Alliances can in turn be implemented on top of common distributed object technology which for its part relies on standard database and communication services.