Adding Constraints to Logic-Based Workflow to Obtain Optimized Schedules

Achievement of an activity generally depends on the achievement of sub-activities. These sub-activities are related with each other in terms of ordering among them and data they access. We can consider a business process as an activity to be achieved and we can deene its sub-activities. The correct and eecient execution of a business process necessitates capturing and deening the relations among sub-activities correctly and eeectively and executing the sub-activities according to this deenition. Working on workkows is a result of such a need. A workkow is a collection of cooperating and coordinated activities designed to carry out a complex task and to achieve the overall goal of this complex task. A workkow management system is a system that completely deenes, manages and executes workkows through the execution of software whose order of execution is driven by a computer representation of the workkow logic ((WFMC 1995]). For the correct and eecient execution of workkows, the speciication should capture all dependencies among sub-activities correctly. There are three main frameworks for specifying workkows: control ow graph temporal constraints triggers The control ow is appropriate for deening local execution dependencies of activities. It is a good tool to depict the overall ow of control. In a typical graph, rst and last activities in the ow, successive activities, AND branches where all of them should be executed in parallel, OR branches where successful execution of only one branch is enough, can be represented. In addition to them, the arcs of the graph can be labeled with conditions, so that the coming activity is executed only if the condition evaluates to true. Figure 1 depicts a simple control ow graph. The control ow graph can be extended by loops, subworkkows, contingency and compensation activities. In most of the commercial workkow management systems block structured workkow deenition languages are used. These languages represent the above features as blocks. Beside local dependencies, it may be necessary to deene global dependencies. These are temporal dependencies such as "if event a is ever executed then b must also be executed ". As explained in Singh 1996], Singh's algebra of temporal constraints can deene almost all of the global dependencies that may arise in workkows. However, global constraints can not model the conditions preceding the activities and can not be used to query the intermediate state of the workkow. Using triggers is another way of deening workkows. Triggers are also …