A Transactional Model for Long-Running Activities

Many computer-supported applications are of long duration and consist of multiple steps that are exe-cuted over possibly heterogeneous servers. Such activ-ities have weaker atomicity requirements than trans-actions. Previously, we illustrated how to organize the execution of such activities using triggers and transac-tions. In this paper, we describe an execution model in.which activities may consist recursively of steps that may be subactivities or transactions. The model defines precisely the semantics of activities: commu-nication between steps and the failure semantics of activities including compensation and exception han-dling. The model also supports querying the status of activities. We also propose an implementation of the model using recoverable queues for reliably chaining the steps according to the semantics of the model. 1