3.1 The problem

Business process reengineering [Ham96] is being used by an increasing number of enterprises to increase their competitiveness. They change their structure from a tayloristic to a process-oriented one to respond faster, more flexibly and efficiently to changing customer requirements. An important means for achieving this goal are workflow-management-systems (wfms) [JB96]. They allow the definition, execution and monitoring of workflows with both human and machine-based actors. Workflows processed in wfms can be described as different aspects, representing discrete modeling domains [Jab95]. Important aspects are the functional aspect, describing the workflow's "task" and its composition of sub-workflows, the control aspect, responsible for directing the workflow execution, the data aspect, covering the data exchange between sub-workflows, the operational aspect, describing the operations performed in the sub-workflows; and the organizational aspect, representing the relation to the organizational structure of the enterprise. Because these aspects are imperative in order to execute a workflow; they are also called imperative aspects. There are also aspects of workflows, which are not necessary to execute them, but increase the quality of their execution. They are called optional aspects. One example is the historical aspect, covering the workflow execution history.
Workflow-management systems are more flexible than traditional applications in supporting process-oriented organizations, because they handle the aspects described above separately and allow for easy adaptation to changed workflows. Traditionally structured applications, however, contain only one "hard-wired" workflow, with no possibility of changing it without modifications to the software. Wfms also differ because they are reflective systems. That means, they "know" about their own state and are capable of changing their behavior accordingly. Furthermore Wfms connect the execution of a business process with the organizational structure of the enterprise. By using role models, wfms can easily transfer work from one person to another. They assure a higher process-quality, because business rules are enforced. Better informed decisions can be made, because wfms are able to collect all the relevant information, the so-called process context, and offer it to the person who makes the decision.
Although wfms offer an impressive list of advantages, their enterprise-wide use is hampered by three major deficiencies. First, they rarely achieve the necessary performance and reliability [AAAM97] to support large numbers of processes. This is due to a centralized architecture, like the one described by [Coa], creating bottlenecks and single failure points [SBMW96]. Second, the ability of wfms to work in heterogeneous and distributed environments is rather limited [GHS95]. Their functionality cannot be transparently distributed across different systems and networks and therefore limits the usefulness of the wfms. Third, to enable enterprise-wide workflows, wfms have to cooperate with a multitude of applications, called legacy applications, in order to perform operations like bookings, etc. The crux of the problem is the software architectures used to build the wfms. They are not appropriate to support the interoperation of independently developed software units, like the wfms and the legacy applications and databases. Furthermore, these architectures do not support the evolution of software systems. However wfms and legacy applications do evolve independently from each other and therefore cause the need for permanent adaptations.