Theory and MethodologyPetri net-based modelling of workflow systems: An overview
Introduction
Workflow management [60], [66] is an organisational process which has always existed [64], but recently it has become the focal point for many researchers and has attracted many commercial companies. The core of workflow systems is the notion of business process [23], which is a set of activities with a common goal. Workflow involves a set of partially ordered activities to be undertaken using human or other resources of the enterprise in order to meet some predefined requirements. Workflow automation allows organisations to become more flexible and adaptable by continuously customising their work to be able to cope with the rapidly changing business environment.
Petri nets are widely studied [72] and successfully applied in different discrete-event dynamic systems, e.g. [35], [50], which are characterised by parallelism and synchronisation. The strong mathematical foundation of Petri nets and the availability of a wide range of supporting tools have made them popular among academic researchers. Petri net-based modelling and analysis of workflow and workflow systems is an active research area in academia, although a small number of vendors [30], [56] have developed Petri net-based workflow management system (WfMS).
This paper presents an overview of existing papers on modelling workflow and workflow systems, which are based on Petri nets. The rest of the paper is organised as follows. In Section 2 a brief introduction to workflow and its terminology is presented. Petri nets and their formal definition are presented in Section 3. In Section 4 a brief review of published papers on Petri net-based modelling of workflow is discussed. Finally, a conclusion derived from the papers reviewed and proposals for future work are presented in Section 5.
Section snippets
Workflow and workflow management system
Although the concept of workflow has been developed from the notion of factory automation [64], its history goes back to the 1970s, when the first prototype of workflow [97] was developed. During the 1970s and 1980s, the notion of Office Information Systems captured a great amount of consideration. Backtalk [75], OfficeTalk-P [42], Office Information System [41], and OfficeTalk-D [40] were introduced as early prototypes for workflow systems. Due to the unavailability of sufficient technology at
Petri nets
Petri nets are a class of modelling tools, which were originated by Petri [78]. They have a well-defined mathematical foundation and an easy-to-understand graphical feature. The graphical nature of Petri nets makes them self-documenting and a powerful design tool, which facilitates visual communication between the people who are engaged in the design process. On the other hand, they are based on a strong mathematical formalism, which makes it possible to set up mathematical models describing
Workflow modelling
Based on their modelling goals, modellers may use different techniques in workflow modelling. For example, Object-Oriented approach [24], workflow loops based on the language/action perspective [73], modified version of the Entity–Relationship (ER) model [27] and transaction model [23] have been successfully used. Existing workflow products suffer from severe limitations [38]. It is criticised [18] that they have (i) no needed functionality, (ii) no clear set of definitions, and (iii) no
Final remarks and conclusion
In this paper we presented an introduction to workflow and workflow systems. We mainly focused on the process definition of workflow, based on the terminology defined by WfMC. A general introduction to Petri nets is covered. Using a nontrivial example, a general methodology to map workflow into Petri nets has been explained. We summarised and classified those available papers, which have concentrated on Petri net-based modelling of workflow. Most of the reviewed papers have used different
Acknowledgements
The authors would like to thank Behrouz Zarei and Peter Kueng for their helpful comments and suggestions on earlier version of the manuscript. The authors also wish to thank anonymous referees for their feedback and comments. This research is sponsored by Persian Gulf University, Bushehr, Iran and MSRT Iran.
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