Juliane Dehnert

Relaxed Soundness of Business Processes

Business processes play a central role in the reorganization of a company and the (re)design of the respective information system(s). Typically the processes are described with the help of a semiformal, graphical language such as the Event-driven Process Chains (EPCs) by Scheer. This approach provides a suitable medium for the communication between the participants: the domain experts and the IT specialists. But these models leave room for interpretation and hence ambiguities which makes them less suitable as a basis for the design of information systems. To remedy this we suggest to transform the EPCs into a formal representation (Petri nets) preserving the ambiguities, i.e. all possibly intended behaviour. Now formal techniques can be used to find out whether the possible behaviours comprise sensible behaviour. If so, we call the net relaxed sound. By not limiting the modeler compared to previous ways (e.g. [8], [3]) we take a pragmatic approach to correctness which only requires that the net represents some valid behaviour. This allows us to draw conclusions on mistakes in the original EPC and to make suggestions for its improvement thereby enhancing both the models quality and its suitability for software engineering.

Reactive Petri nets for workflow modeling

Petri nets are widely used for modeling and analyzing workflows. Using the token-game semantics, Petri net-based workflow models can be analyzed before the model is actually used at run time. At run time, a workflow model prescribes behavior of a reactive system (the workflow engine). But the token-game semantics models behavior of closed, active systems. Thus, the token-game semantics behavior of a Petri net-based workflow model will differ considerably from its behavior at run time. In this paper we define a reactive semantics for Petri nets. This semantics can model behavior of a reactive system and its environment. We compare this semantics with the token-game semantics and prove that under some conditions the reactive semantics and the token-game semantics induce similar behavior. Next, we apply the reactive semantics to workflow modeling and show how a workflow net can be transformed into a reactive workflow net. We prove that under some conditions the soundness property of a workflow net is preserved when the workflow net is transformed into a reactive workflow net. This result shows that to analyze soundness, the token-game semantics can safely be used, even though that semantics is not reactive.

On the suitability of correctness criteria for business process models

A popular requirement for the validation of workflow models is soundness. As soundness can not be easily seen on the model level, different correctness criteria have been proposed in the literature to bridge the gap between the modeling process and a executable workflow model. Well-structuredness and relaxed soundness are investigated in the paper. Relationships between the properties are derived.

Customized atomicity specification for transactional workflows

We introduce a new approach for specifying transaction management requirements for workflow applications. We propose independent models for the specification of workflow and transaction properties. Although we distinguish multiple transaction properties in our approach, we focus on atomicity. We propose an intuitive notation to specify atomicity and provide generic rules to integrate the workflow specification and the atomicity specification into one single model based on Petri nets. The integrated model can be checked for correctness. We call this correctness criterion relaxed soundness as a weaker notion of the existing soundness criterion. We can relax the correctness criterion because we rely on run-time transaction management. A real life example shows the applicability of the concepts.

Modelling and evaluation of time aspects in business processes

There is a need for modelling and performance evaluation techniques and tools for a fast and reliable design of workflow systems. This paper introduces a modelling methodology based on coloured stochastic Petri nets. It allows the integration of control flow, organizational, information related and timing aspects in one modelling framework. The processing delays include stochastic distributions in addition to deterministic times. Several workflows and the effects of constrained shared resources needed for different tasks can easily be described and analysed together. Control flow and organizational aspects are modelled separately in resource and workflow models. These models are automatically compiled into one model, which can then be used for qualitative analysis or performance evaluation. The proposed modelling and evaluation method is supported by the software tool TimeNET. An application example shows its use.

The Petri Net Baukasten of the DFG Forschergruppe PETRI NET TECHNOLOGY

In the long history of Petri nets a universe of Petri nets has evolved consisting of an enormously rich theory, a wide variety of tools, and numerous successful applications and case studies in various application domains. This vast variety is not any more handable for anyone working with Petri nets, which results in the strong need of a structured access to Petri nets. This structured access has been the main aim of the DFG-Forschergruppe PETRI NET TECHNOLOGY, which has developed the so-called Petri Net Baukasten for this purpose. It is designed to support Petri net experts, application developers and tool developers alike in their specific work with Petri nets. This paper presents an overview of the concepts, initial and 2nd installment of the Petri Net Baukasten, which have been presented at the 1st and 2nd International Colloquium on Petri Net Technologies for Modelling Communication Based Systems in 1999 and 2001, respectively.

Making Workflow Models Sound Using Petri Net Controller Synthesis

More and more companies use ”process aware” information systems to make their business processes more efficient. To do this, workflow definitions must be formulated in a formal specification language, as they represent executable derivates of business process descriptions. Both for the less formal descriptions of business processes as well as the workflow definitions, Petri-net based approaches are used successfully. In the literature the business process descriptions are required to be well-structured, leading to a sound workflow definition. We argue that in many cases well-structuredness is too restrictive for practitioners. Relaxed soundness has been introduced previously as a more suitable requirement. The paper presents how methods from controller synthesis for Petri nets can be used to automatically make this type of models sound. For this reason we adopt the idea of controllability for Petri net workflow models.

Four Steps Towards Sound Business Process Models

Supporting the everyday operation of business processes with the help of workflow management systems is a necessary prerequisite for many companies in order to stay competitive. Managing business processes comprises their modeling, analysis and execution support. Although investigated since the beginning of the nineties there is still a gap between the possibilities of the provided modeling languages, the expertise of the modeler and the requirements posed through the different steps within the management of business processes.

Non-controllable Choice Robustness Expressing the Controllability of Workflow Processes

Workflow systems are reactive systems. They run in parallel with their environment. They respond to external events and produce events which again have certain effects in the environment. Most approaches in modeling workflow systems assume reasonable behavior of the environment. They disregard malicious requests such as e.g. denial-of-service attacks or hacker attacks trying to misuse the provided services. Hence they do not provide the modeler with a means to check whether their processes react robustly to any possible request from the environment. In this paper we will propose a means to overcome this deficiency. Based on the modeling with Workflow nets we will introduce a new correctness criterion, called non-controllable choice robustness. This criterion depicts the ability of a workflow system to react to possible requests from the environment and still guarantee some desired objective. For the definition and the algorithmical installment of noncontrollable choice robustness parallels to Game Theory are drawn.

The Petri Net Baukasten: 2nd Installment1

Abstract Petri nets are a subject of interest to researchers since more than 30 years. They became popular since they allow the graphic representation of computational structures and have a formal underpinning that allows formal proofs of properties. Their use in engineering, however is limited to a rather small number of applications. Many of the graphic notations used in practice are very similar to the graphic representation of Petri nets but do not make use of the rich body of theory that exists for Petri nets. This is repeatedly attributed to the fact that Petri nets and the associated theory are hard to understand and real life problems modelled with Petri nets tend to require special brands of Petri nets which in turn led to a great variety of different net types. Finding the right Petri net types from the portfolio of existing types, finding corresponding techniques and tools, selecting them and applying them successfully to applications poses a problem and prevents their wide spread use. In order to improve this situation, a Petri Net Baukasten has been developed by the DFG-Forschergruppe Petri Net Technology in Berlin. It aims at the development of a support environment for the use of Petri nets in new applications including theoretical and tool aspects. This paper presents the 2nd Installment of the Petri Net Baukasten, which extends the first installment of the Petri Net Baukasten, documented as Initial Realization in 1999, by providing interfaces, services, and data for specific user groups such as application developers, tool developers and Petri net experts. The user interface offers an intuitive presentation of Petri net concepts and notions. The Petri Net Baukasten supports different user groups in their specific work with Petri nets by user specific assistence services. These services allow the users to find the right Petri net types in a variety of existing types and support their selection and use. Information is kept in an associated database. Furthermore the assistence services maintain this database in order to keep track of recent developments in theory, tools and application areas.