Declarative Workflow Modeling with UML Class Diagrams and OCL

This paper describes an approach of modeling workflows with UML class diagrams and OCL constraints [OCL06] in a declarative way. These are modeled in the UML tool USE [USE08] that can generate object diagrams (snapshots) out of UML class diagrams. USE checks specified OCL constraints against the generated snapshots. With the declarative workflow modeling approach presented here, activity model states are integrated in the object model states. By analyzing these snapshots the model is validated against requirements. In figure 1 a UML class diagram for modeling flat workflows is presented. The class Process has an attribute name and contains a set of activities which is described by the association belongs between Process and Activity. Atomic actions in the process that are executed in the workflow are expressed by the class Activity. Activities have also names that describe the actions and a state in which the activity is just in the time, the snapshot of the system is taken. Possible states for the activities are described in the enumeration State. A derived state of the process depends on the states of the included activities and is delivered by the operation getState in the class Process. Further on, the operation getActivity is needed by the subsequent OCL constraints and returns the requested activity instance. The described operations are specified in OCL expressions and will be interpreted by USE. Figure 1: UML model for flat workflow specifications modeled in USE Actual states of an activity instance can be changed by invoking the methods skip(), start() or done().The functionality of the operations are expressed by OCL preand postconditions. Operation enabled() proves on basis of the current object model state and the inner state of the activity itself, if it is enabled and thus can be started. This method is also coded in an OCL expression.