Workflow-Net Based Cooperative Multi-Agent Systems

Workflow-nets are mathematical frameworks that are used to formally describe, model and implement workflows. First, we propose critical section workflow nets (abbreviated WFCSnet). This framework allows feedbacks in workflow systems while ensuring the soundness of the workflow. Feedback is generally not recommended in workflow systems as they threaten the soundness of the system. The proposed WFCSnet allows safe feedback and limits the maximum number of activities per workflow as required. A theorem for soundness of WFCSnet is presented. Serializability, Separability, Quasi-liveness and CS-Properties of WFCSnet are examined and some theorems and lemmas are proposed to mathematically formalize them. In this thesis, we define some formal constructs that we then build upon. We define the smallest formal sub-workflow that we call a unit. We propose some mathematical characteristics for the unit and show how it can be used. We study similarities between units and whether two units can be used interchangeably or not. We then use composites out of simple units to build more complex constructs and we study their properties. We define the concept of cooperation and propose a mathematical definition of the concept. We discuss the concept of task coverage and how it affects cooperation. We claim that task coverage is necessary for any task to be achieved and therefore, a necessity for cooperation. We use mathematical methods to determine the task coverage and the candidate cooperative partners based on their capabilities that can contribute to the desired task. Workflow-net based cooperative behaviour among agents is proposed. First, we propose a cooperative algebra, which takes the desired objective of cooperation as a plan and then transforms this plan into a workflow-net structure describing dependencies and concurrency among sub-workflow elements constituting the overall plan. Our proposed cooperative algebra converts the plan into a set of matrices that model the cooperative workflow among agents. We then propose a cooperative framework with operators that assign tasks to agents based on their capabilities to achieve the required task

Transition Systems, Event Structures and Unfoldings

Elementary transition systems were introduced by the authors in DAIMI PB-310. They were proved to be, in a strong categorical sense, the transition system version of elementray net systems. The question arises whether the notion of a region and the axioms (mostly based on regions) imposed on ordinary transition systems to obtain elementray net systems. Stated differently, one colud ask whether elementray transition systems could also play a role in characterizing other models of concurrency. We show here that by smoothly stengthening the axioms of elementary transition systems one obtains a subclass called occurrence transitions systems which turn out to be categorically equivalent to the well-known model of concurrency called prime event structures. Next we show that occurrence transition systems are to elementry transition systems what occurrence nets are to elementary nets systems. We define an ''unfold'' operation on elementry transition systems which yields occurrence transistion systems. We then prove that this operation uniquely extends to a functor which is the right adjoint to the inclusion functor from (the full subcategory of) occurrence transition systems to (the category of) elementary transition systems. Thus the results of this paper also show that the semantic theory of elementray net systems has a nice counterpart in the more abstract world of transition systems

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

Recent advances in petri nets and concurrency

CEUR Workshop Proceeding