Recent advances in petri nets and concurrency

CEUR Workshop Proceeding

Symbolic Supervisory Control of Resource Allocation Systems

<p>Supervisory control theory (SCT) is a formal model-based methodology for verification and synthesis of supervisors for discrete event systems (DES). The main goal is to guarantee that the closed-loop system fulfills given specifications. SCT has great promise to assist engineers with the generation of reliable control functions. This is, for instance, beneficial to manufacturing systems where both products and production equipment might change frequently.</p> <p>The industrial acceptance of SCT, however, has been limited for at least two reasons: (i) the analysis of DES involves an intrinsic difficulty known as the state-space explosion problem, which makes the explicit enumeration of enormous state-spaces for industrial systems intractable; (ii) the synthesized supervisor, represented as a deterministic finite automaton (FA) or an extended finite automaton (EFA), is not straightforward to implement in an industrial controller.</p> <p>In this thesis, to address the aforementioned issues, we study the modeling, synthesis and supervisor representation of DES using binary decision diagrams (BDDs), a compact data structure for representing DES models symbolically. We propose different kinds of BDD-based algorithms for exploring the symbolically represented state-spaces in an effort to improve the abilities of existing supervisor synthesis approaches to handle large-scale DES and represent the obtained supervisors appropriately.</p> <p>Following this spirit, we bring the efficiencies of BDD into a particular DES application domain -- deadlock avoidance for resource allocation systems (RAS) -- a problem that arises in many technological systems including flexible manufacturing systems and multi-threaded software. We propose a framework for the effective and computationally efficient development of the maximally permissive deadlock avoidance policy (DAP) for various RAS classes. Besides the employment of symbolic computation, special structural properties that are possessed by RAS are utilized by the symbolic algorithms to gain additional efficiencies in the computation of the sought DAP. Furthermore, to bridge the gap between the BDD-based representation of the target DAP and its actual industrial realization, we extend this work by introducing a procedure that generates a set of "guard" predicates to represent the resulting DAP.</p> <p>The work presented in this thesis has been implemented in the SCT tool Supremica. Computational benchmarks have manifested the superiority of the proposed algorithms with respect to the previously published results. Hence, the work holds a strong potential for providing robust, practical and efficient solutions to a broad range of supervisory control and deadlock avoidance problems that are experienced in the considered DES application domain.</p

Sixth Workshop and Tutorial on Practical Use of Coloured Petri Nets and the CPN Tools Aarhus, Denmark, October 24-26, 2005

This booklet contains the proceedings of the Sixth Workshop on Practical Use of Coloured Petri Nets and the CPN Tools, October 24-26, 2005. The workshop is organised by the CPN group at the Department of Computer Science, University of Aarhus, Denmark. The papers are also available in electronic form via the web pages: http://www.daimi.au.dk/CPnets/workshop0

A methodology for workflow modeling : From business process modeling towards sound workflow specification

Der Einsatz von Workflow Management Systemen (WFMS) in Unternehmen oder Verwaltungen mit einfach strukturierten und automatisierbaren Prozessen bietet ein hohes Potenzial für die Optimierung der Geschäftsprozesse. Für die Koordinierung von Geschäftsprozessen zur Laufzeit benötigen WFMS Workflow-Spezifikationen, die den automatisierbaren Anteil der Geschäftsprozesse in einer maschinenlesbaren Form beschreiben. In der Praxis werden Workflow-Spezifikationen bislang oft unabhängig von bereits existierenden Geschäftsprozessmodellen erstellt. Es existiert kein methodisch fundiertes Vorgehensmodell, dass die Modellierung von Gechäftsprozessen und die Weiterverwendung der erstellten Modelle für die Workflow-Spezifikation unterstützt [GHS95,AaHe02]. Diese Arbeit schlägt ein durchgehendes Vorgehensmodell für die Spezifikation von Workflows in Form von Petrinetzen vor. In dem fünfstufigen Vorgehensmodell wird der Schwerpunkt auf die Modellierung der Kontrollflussaspekte gelegt. Im Rahmen der Modellierung werden die folgenden Schritte unterstützt: 1. Modellierung der Geschäftsprozesse 2. Formalisierung durch Petrinetze 3. Korrektheitstest und Fehlerkorrektur 4. Festlegung und Integration einer Ausführungsstrategie 5. Kontrollverfeinerung. Das Ergebnis ist ein Prozessmodell mit formal fundierter und operationaler Semantik, das zudem sound [Aal98] ist. Ein solches Modell entspricht den Anforderungen an eine Workflow-Spezifikation, deren Verwendung für ein WFMS eine zuverlässige Ausführung der Geschäftsprozesse zur Laufzeit garantiert. In dem ersten Schritt "Modellierung der Geschäftsprozesse" wird die Verwendung semiformaler Modellierungstechniken unterstützt. Diese räumen dem Modellierer Spielraum in der Beschreibung der Prozesse ein. Im nächsten Schritt wird das erstellte Modell intern formalisiert. Die Formalisierung basiert auf einer Abbildung in Petrinetze. Dabei werden Mehrdeutigkeiten nicht eliminiert sondern explizit gemacht. Im dritten Schritt wird das Modell auf Korrektheit überprüft. Dafür werden neue, pragmatische Kriterien eingeführt. Es werden präzise Fehlermeldungen zurückgegeben, die ein iteratives Verbessern der Geschäftsprozessmodelle ermöglichen. In Schritt vier und fünf wird das erstellte Modell auf eine Workflow-Spezifikation abgebildet. Dazu wird auf die bereits erstellte Petrinetz-Formalisierung zurückgegriffen. Die Petrinetze werden zunächst so erweitert, dass eine Ausführungsstrategie festgelegt wird. Durch die Integration der Strategie werden alle vorher noch enthaltenen Mehrdeutigkeiten beseitigt. Abschließend werden Aktivitäten verfeinert. Das vorgeschlagene Vorgehensmodell bindet in der Praxis bewährte Techniken ein und stellt angemessene Kriterien für die Fehlerkorrektur zur Verfügung. Das gesamte Vorgehensmodells ist methodisch unterlegt und greift auf Ergebnisse der Petrinetztheorie, der Spieltheorie und der Controller Synthesis zurück.Supporting business processes with the help of workflow management systems is a necessary prerequisite for many companies to stay competitive. An important task is the specification of workflow, i.e. these parts of a business process that can be supported by a computer system. A workflow specification mainly refines a business process description, incorporating details of the implementation. Despite the close relation between the two process descriptions there is still no satisfactory link between their modeling. This fact mainly relies on the assignment to different peolpe (IT- vs. domain experts) having a different modeling culture. The thesis provides a methodically well-founded approach for the specification of functional workflow requirements. It supports domain experts in their modeling of business processes in a semiformal manner and guides them stepwise towards a formal workflow specification, i.e. helping to bridge the gap between business process modeling and workflow specification. The proposed approach acknowledges the need to describe business processes at different levels of abstraction and combines the advantages of different modeling languages that proved to fit the respective requirements. A semiformal modeling language is proposed to be used by the domain expert. As a prominent example, widely accepted in practice, are Event-driven Process Chains (EPCs). For the definition of the workflow specification we use a particular type of Petri nets. The strength of Petri-nets is their formally founded, operational semantics which enables their use as input format for workflow management systems. The key concept for the proposed process model is the use of pragmatic correctness criteria, namely relaxed soundness and robustness. They fit the correctness requirements within this first abstraction level and make it possible to provide a feedback to the modeler. To support the execution of the business process at run time, the resulting process description must be refined to fit the requirements of a workflow specification. The proposed process model supports this refinement step, applying methods from controller synthesis. A sound WF-system is automatically generated on the basis of a relaxed sound and robust process description. Only within this step do performance issues become relevant. Information that is incorporated relates to a certain scheduling strategy. The late determination of performance issues is especially desirable as corresponding information (the occurrence probability of a certain failure, costs of failure compensation, or priorities) will often only become available at run-time. Their incorporation towards the end of the proposed process model extends the possibility to reuse modeling results under changing priorities. The resulting process description is sound. Using it as a basis for the execution support during run-time reliable processing can be guaranteed

Tools and Algorithms for the Construction and Analysis of Systems

This open access two-volume set constitutes the proceedings of the 27th International Conference on Tools and Algorithms for the Construction and Analysis of Systems, TACAS 2021, which was held during March 27 – April 1, 2021, as part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2021. The conference was planned to take place in Luxembourg and changed to an online format due to the COVID-19 pandemic. The total of 41 full papers presented in the proceedings was carefully reviewed and selected from 141 submissions. The volume also contains 7 tool papers; 6 Tool Demo papers, 9 SV-Comp Competition Papers. The papers are organized in topical sections as follows: Part I: Game Theory; SMT Verification; Probabilities; Timed Systems; Neural Networks; Analysis of Network Communication. Part II: Verification Techniques (not SMT); Case Studies; Proof Generation/Validation; Tool Papers; Tool Demo Papers; SV-Comp Tool Competition Papers

Computer Aided Verification

This open access two-volume set LNCS 13371 and 13372 constitutes the refereed proceedings of the 34rd International Conference on Computer Aided Verification, CAV 2022, which was held in Haifa, Israel, in August 2022. The 40 full papers presented together with 9 tool papers and 2 case studies were carefully reviewed and selected from 209 submissions. The papers were organized in the following topical sections: Part I: Invited papers; formal methods for probabilistic programs; formal methods for neural networks; software Verification and model checking; hyperproperties and security; formal methods for hardware, cyber-physical, and hybrid systems. Part II: Probabilistic techniques; automata and logic; deductive verification and decision procedures; machine learning; synthesis and concurrency. This is an open access book

Dynamic Workflow-Engine

We present and assess the novel thesis that a language commonly accepted for requirement elicitation is worth using for configuration of business process automation systems. We suggest that Cockburn's well accepted requirements elicitation language - the written use case language, with a few extensions, ought to be used as a workflow modelling language. We evaluate our thesis by studying in detail an industrial implementation of a workflow engine whose workflow modelling language is our extended written use case language; by surveying the variety of business processes that can be expressed by our extended written use case language; and by empirically assessing the readability of our extended written use case language. Our contribution is sixfold: (i) an architecture with which a workflow engine whose workflow modelling language is an extended written use case language can be built, configured, used and monitored; (ii) a detailed study of an industrial implementation of use case oriented workflow engine; (iii) assessment of the expressive power of the extended written use case language which is based on a known pattern catalogue; (iv) another assessments of the expressive power of the extended written use case language which is based on an equivalence to a formal model that is known to be expressive; (v) an empirical evaluation in industrial context of the readability of our extended written use case language in comparison to the readability of the incumbent graphical languages; and (vi) reflections upon the state of the art, methodologies, our results, and opportunities for further research. Our conclusions are that a workflow engine whose workflow modelling language is an extended written use case language can be built, configured, used and monitored; that in an environment that calls upon an extended written use case language as a workflow modelling language, the transition between the modelling and verification state, enactment state, and monitoring state is dynamic; that a use case oriented workflow engine was implemented in industrial settings and that the approach was well accepted by management, workflow configuration officers and workflow participants alike; that the extended written use case language is quite expressive, as much as the incumbent graphical languages; and that in industrial context an extended written use case language is an efficient communication device amongst stakeholders