Formal Aspects of Workkow Management Part 2: Distributed Scheduling

Work ows are composite activities that achieve interoperation of a variety of system and human tasks. Work ows must satisfy subtle domain-speci c integrity and organizational requirements. Consequently, exibility in execution is crucial. A promising means to achieve exibility is through declarative speci cations (Part 1) with automatic distributed scheduling techniques (Part 2). We address the problem of scheduling work ows from declarative speci cations given in terms of intertask dependencies and event attributes. Our approach involves distributed events, which are automatically set up to exchange the necessary messages. Our approach uses symbolic reasoning to (a) determine the initial constraints on events or guards, (b) preprocess the guards, and (c) execute the events. It has been implemented. work ows, temporal logic, scheduling. This is a greatly extended and revised version of a paper that appears in the Proceedings of the International Conference on Data Engineering (ICDE), held in New Orleans in February 1996. Some of the preliminary work of this paper was performed in the Carnot Project at MCC. I participated in discussions with Paul Attie, Greg Meredith, and Chris Tomlinson. Many signi cant revisions and enhancements|including a new formal semantics, all proofs, most de nitions, and most theorems|were made at NCSU. I have bene ted from discussions with Neerja Bhatt, Anuj Jain, and Chubin Lin, and comments from Krithi Ramamritham. Partially supported by the NCSU College of Engineering, by the National Science Foundation under grants IRI-9529179 and IRI-9624425, and by IBM.