1995 Reports

A Paradigm for Decentralized Process Modeling and Its Realization in the Oz Environment

Ben-Shaul, Israel Z.

A Paradigm for Decentralized Process Modeling and its Realization in the Oz Environment Israel Z. Ben-Shaul This dissertation investigates decentralization of software processes and Process Centered Environments (PCEs), and addresses a wide range of issues concerned with supporting interoperability and collaboration among autonomous and heterogeneous processes, both in their definition and in their execution in possibly physically dispersed PCEs. Decentralization is addressed at three distinct levels of abstraction. The first proposes a generic conceptual model that is both language- and PCE-independent. The second level explores the realization of the model in a specific PCE, Oz, and its rule-based process modeling language. The third level addresses architectural issues in interconnecting autonomous PCEs as a basis for process interoperability. Two key concerns guide this research. The first is maximizing local autonomy, so as not to force a priori any global constraints on the definition and execution of local processes, unless explicitly and voluntarily specified by a particular process instance. The second concern is tailorability, dynamicity and fine-grained control over the degree of interoperability. The essence of the interoperability model lies in two abstraction mechanisms -- Treaty and Summit-- for inter-process definition and execution, respectively. Treaties enable to specify shared sub-processes while retaining the privacy of local sub-processes. To promote autonomy, Treaties are established by explicit and active participation of the involved processes. To promote fine granularity, Treaties are defined pairwise between two collaborating processes and formed over a possibly small sub-process unit, although multisite Treaties over large shared sub-processes can be constructed, if desired. Finally, Treaties are superimposed on top of pre-existing instantiated processes, enabling their dynamic and incremental establishment and supporting a decentralized bottom-up approach. Summits are the execution counterparts of Treaties. They support “global“ execution of shared sub-processes involving artifacts and/or users from multiple sites, as well as local execution of private sub-processes. Summits successively alternate between shared and private execution modes, where the former is used for synchronous execution of shared activities, and the latter for autonomous execution of any private subtasks emanating from the shared activities as defined in the local processes.