Formalization of Workflows and Correctness Issues in the Presence of Concurrency

  • Authors:

  • Ïsmaïlcem Budak Arpinar;Uğur Halici;Sena Arpinar;Asuman Doğaç

  • Affiliations:

  • Software Research and Development Center, Department of Computer;Software Research and Development Center, Department of Computer Engineering, Middle East Technical University (METU), 06531, Ankara, Turkey. halici@rorqual.cc.metu.edu.tr;Software Research and Development Center, Department of Computer Engineering, Middle East Technical University (METU), 06531, Ankara, Turkey. nural@srdc.metu.edu.tr;Software Research and Development Center, Department of Computer Engineering, Middle East Technical University (METU), 06531, Ankara, Turkey. asuman@srdc.metu.edu.tr

  • Venue:
  • Distributed and Parallel Databases - Special issue on electronic commerce
  • Year:
  • 1999

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Abstract

In this paper, main components of a workflow system that are relevant to the correctnessin the presence of concurrency are formalized based on set theory and graph theory. Theformalization which constitutes the theoretical basis of the correctness criterion provided can be summarized as follows:-Activities of a workflow are represented through a notation based onset theory to make it possible to formalize the conceptual groupingof activities.-Control-flow is represented as a special graph based on this set definition, and it includes serial composition, parallel composition, conditional branching, and nesting of individual activities and conceptual activities themselves.-Data-flow is represented as a directed acyclic graph in conformance with the control-flow graph.The formalization of correctness of concurrently executing workflow instances is based on this framework by definingtwo categories of constraints on the workflow environment with which theworkflow instances and their activities interact. These categories are:-Basic constraints that specify the correct states of a workflow environment.-Inter-activity constraints that define the semantic dependencies among activities such as an activity requiring the validity of aconstraint that is set or verified by apreceding activity.Basic constraints graph and inter-activity constraints graph which are in conformance with the control-flowand data-flow graphs are then defined to represent these constraints. Thesegraphs are used in formalizing the intervals among activities where aninter-activity constraint should be maintained and the intervals where abasic constraint remains invalid.A correctness criterion is defined for an interleaved executionof workflow instancesusing the constraints graphs. A concurrency control mechanism,namely Constraint Based Concurrency Control technique isdeveloped based on the correctnesscriterion. The performance analysis shows the superiority of theproposed technique. Other possible approaches to the problem are also presented.