The Declare Service

The Declare Service is a YAWL Custom Service that enables decomposing YAWL tasks into DECLARE workflows, i.e. workflows supported by the workflow management system (WfMS) called DECLARE. The goal of this service is to enable a particular kind of flexibility. Chapter 6 describes a constraint-based approach to workflow models and the ConDec language. This approach, supported by the DECLARE WfMS, allows for more flexibility, i.e. execution of tasks is allowed if it is not explicitly forbidden by some constraint. This chapter describes DECLARE and the Declare Service for YAWL. Sometimes it is easier to express a process in a procedural language (e.g. the native workflow language of YAWL) and sometimes a declarative approach is more suitable. Moreover, in a larger process it may be useful to express parts of the process in a procedural language and specify other parts in terms of constraints. Using the service-oriented architecture of YAWL, this can easily be realized. A YAWL task may decompose into a DECLARE process and a task in DECLARE can be decomposed into a YAWL process. Arbitrary decompositions of DECLARE and YAWL models allow for the integration of declarative and YAWL workflows on different abstraction levels.1 This way the designer is not forced to make a binary choice between a declarative and a procedural way of modeling. Hence, a seamless integration can be achieved, where parts of the workflow that need a high degree of flexibility are supported by declarative DECLARE models and parts of the processes that need centralized control of the system are supported by YAWL models. Consider, for example, the decomposition of the Carrier Appointment process shown in Figure 12.1. At the highest level of decomposition, the main process is modeled using a procedural YAWL Carrier Appointment net, which is described in Appendix A. However, the parts of the net that refer to the Truck Load and Less than