Starts with a brief review of the history and the application areas considered in the literature. The author then proceeds with introductory modeling examples, behavioral and structural properties, three methods of analysis, subclasses of Petri nets and their analysis. In particular, one section is devoted to marked graphs, the concurrent system model most amenable to analysis. Introductory discussions on stochastic nets with their application to performance modeling, and on high-level nets with their application to logic programming, are provided. Also included are recent results on reachability criteria. Suggestions are provided for further reading on many subject areas of Petri nets. >

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Petri nets: Properties, analysis and applications

Workflow management promises a new solution to an age-old problem: controlling, monitoring, optimizing and supporting business processes. What is new about workflow management is the explicit representation of the business process logic which allows for computerized support. This paper discusses the use of Petri nets in the context of workflow management. Petri nets are an established tool for modeling and analyzing processes. On the one hand, Petri nets can be used as a design language for the specification of complex workflows. On the other hand, Petri net theory provides for powerful analysis techniques which can be used to verify the correctness of workflow procedures. This paper introduces workflow management as an application domain for Petri nets, presents state-of-the-art results with respect to the verification of workflows, and highlights some Petri-net-based workflow tools.

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The application of Petri-nets to workflow management

Differences in features supported by the various contemporary commercial workflow management systems point to different insights of suitability and different levels of expressive power. The challenge, which we undertake in this paper, is to systematically address workflow requirements, from basic to complex. Many of the more complex requirements identified, recur quite frequently in the analysis phases of workflow projects, however their implementation is uncertain in current products. Requirements for workflow languages are indicated through workflow patterns. In this context, patterns address business requirements in an imperative workflow style expression, but are removed from specific workflow languages. The paper describes a number of workflow patterns addressing what we believe identify comprehensive workflow functionality. These patterns provide the basis for an in-depth comparison of a number of commercially available workflow management systems. As such, this paper can be seen as the academic response to evaluations made by prestigious consulting companies. Typically, these evaluations hardly consider the workflow modeling language and routing capabilities, and focus more on the purely technical and commercial aspects.

Workflow Patterns

Generalized stochastic Petri nets (GSPNs) are presented and are applied to the performance evaluation of multiprocessor systems. GSPNs are derived from standard Petri nets by partitioning the set of transitions into two subsets comprising timed and immediate transitions. An exponentially distributed random firing time is associated with each timed transition, whereas immediate transitions fire in zero time. It is shown that GSPN are equivalent to continuous-time stochastic processes, and solution methods for the derivation of the steady state probability distribution are presented. Examples of application of gspn models to the performance evaluation of multiprocessor systems show the usefulness and the effectiveness of this modeling tool. 15 references.

A class of generalized stochastic Petri nets for the performance evaluation of multiprocessor systems

http://www.workflowpatterns.com/documentation/documents/yawl_qut_report_FIT-TR-2002-06.pdf

YAWL: yet another workflow language

Open systems

Automated office systems are emerging as an interdisciplinary research area with a strong computer science component. In this paper office information systems are defined as entities which perform document storage, retrieval, manipulation, and control within a distributed environment. Some state-of-the-art implementations are described. The research is related to different areas of computer science and several detailed examples are provided.

Office Information Systems and Computer Science

Petri net models and variants thereof have primarily been used to model structured systems such as computer programs, factory production lines, and engineering hardware. In contrast, this paper discusses the issues and challenges in the modeling of human activity in the workplace. This type of activity frequently has a large component that is unstructured, creative work. It is dynamic and difficult to capture via traditional Petri nets. Our research group at the University of Colorado has been investigating Information Control Nets (ICNs), derived from high level Petri nets, as a tool for modeling office workflow. After carefully explaining the notion of Workflow, this paper presents a formal (and also an informal) definition of ICN. We illustrate the utility of ICNs via an office analysis example.

Modeling and Enactment of Workflow Systems

High bandwidth applications with time-dependent resource requirements demand certain resource level assurances in order to operate correctly. Quality of service resource management techniques are being successfully developed that allow network systems to provide such assurances. These solutions generally assume that the operating system at either end of the network is capable of handling the throughput requirements of the applications. However, real operating systems have to manage many concurrent applications with varying resource requirements. Without specialized support, the operating system cannot guarantee the resources needed for any particular application. In support of these kinds of applications we have developed a middleware agent called a dynamic QoS manager (DQM) that mediates application resource usage so as to ensure that applications get the resources they need in order to provide adequate performance. The DQM employs a variety of algorithms to determine application resource allocations. Using application QoS levels, it provides for resource availability based algorithmic variation within applications and varying application periods. It also allows for inaccurate application resource usage estimates through a technique we have developed called dynamic estimate refinement. The paper discusses new developments in the design of the DQM and presents results showing DQM performance with both real and synthetic applications.

A dynamic quality of service middleware agent for mediating application resource usage

An extension of Petri nets called evaluation nets (E-nets) has been developed for use in representation of computer systems. These lead to interpreted graphs for use in human communication and to machine-interpretable descriptions. They may be used as aids in development of simulations and planning of measurements for examining characteristics such as throughput, turnaround time, and utilization of resources. This paper reviews the five primitives used to form nets expressing logical interactions among tokens (or tasks) flowing through the net and system resources represented by the net. Inherent in the use of the primitives is the ability to express time delays associated with the flow of tokens through the network and the modification of attributes of these tokens. This paper extends previous work on evaluation nets through the use of macro nets that represent structures made up of the primitives, allowing compression of the net for easier understanding. The macro nets are ``open-ended'' in the sense that the user can develop new macros to suit the needs of a particular study. Evaluation nets can be used informally like flow charts or block diagrams, although they provide greater power of expression than either. They can also be used more formally to develop machine aids, e.g., for on-line editing of evaluation nets or for development of simulation programs. Some examples of evaluation nets are provided that model a CDC 6400 and the cooperation of n independent sequential processes.

Gary J. Nutt

Papers

Open systems

Office Information Systems and Computer Science

Modeling and Enactment of Workflow Systems

A dynamic quality of service middleware agent for mediating application resource usage

Macro E-Nets for Representation of Parallel Systems