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1

Defining Multi-Party Compromises using Unfoldings of Workflow Nets

Köhler-Bußmeier M.

Fundamenta Informaticae

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2013

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Vol. 128, nr 1-2

97--111

EN

In this paper we develop a negotiation and contracting framework for inter-organisational workflows. The overall aim is to compute a group-plan from a given set of individual plans, where plans are formulated in the context of a given inter-organisational workflow between the agents. A general problem is that the individual plans are not consistent, i.e. the intersection of all individual plans does not contain a complete process, which leads from the initial state of the workflow to its final state. Therefore, negotiation is needed to obtain a compromise. In this paper we develop a generic negotiation protocol and use branching processes as the elementary data structure. The generic protocol is adapted within the specifics of our SONAR-framework. SONAR is a specification framework that defines the organisational structure of multi-agent systems. SONAR has a formal notion of teams and team-formation which is used here to instantiate the strategy parameters.

2

Unfolding Semantics of Petri Nets Based on Token Flows

Bergenthum R., Mauser S., Lorenz R., Juhas G.

Fundamenta Informaticae

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2009

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Vol. 94, nr 3/4

331-360

EN

In this paper we propose two new unfolding semantics for general Petri nets combining the concept of prime event structures with the idea of token flows developed in [13]. In contrast to the standard unfolding based on branching processes, one of the presented unfolding models avoids to represent isomorphic processes while the other additionally reduces the number of (possibly nonisomorphic) processes with isomorphic underlying runs. We show that both the proposed unfolding models still represent the complete partial order behavior. Moreover, in both cases it is possible to construct complete finite prefixes for bounded nets through applying the known theory of cut-off events. In particular, canonical prefixesw.r.t. a given cutting context can be defined and computed for bounded nets. We present implementations of construction algorithms for complete finite prefixes of both the unfolding models. Experimental results show that the computed prefixes are much smaller and can be constructed significantly faster than in the case of the standard unfolding.

3

Modular Construction of Finite and Complete Prefixes of Petri net Unfoldings

Madalinski A., Fabre E.

Fundamenta Informaticae

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2009

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Vol. 95, nr 1

219-244

EN

This paper considers distributed systems, defined as a collection of components interacting through interfaces. Components, interfaces and distributed systems are modeled as Petri nets. It is well known that the unfolding of such a distributed system factorises, in the sense that it can be expressed as the composition of unfoldings of its components. This factorised form of the unfolding generally provides a more compact representation of the system runs, because each component does not need to represent the possible choices (conflicts) appearing in the other components. Moreover, the unfolding factorisation makes it possible to analyse the system by parts. The paper focuses on the derivation of a finite and complete prefix (FCP) in the unfolding of a distributed system. Specifically, one would like to directly obtain such a FCP in factorised form, without computing first a FCP of the global distributed system and then factorising it. The construction of such a “modular FCP” is based on deriving summaries of component behaviours w.r.t. their interfaces, that are then communicated to the neighbouring components. The latter combine these summaries with their local behaviours, and prepare interface summaries for the next components. This globally takes the form of a message passing algorithm, where the global system is never considered.

4

Reachability in Contextual Nets

Winkowski J.

Fundamenta Informaticae

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2002

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Vol. 51, nr 1,2

235-250

EN

Contextual nets, or Petri nets with read arcs, are models of concurrent systems with context dependent actions. The problem of reachability in such nets consists in finding a sequence of transitions that leads from the initial marking of a given contextual net to a given goal marking. The solution to this problem that is presented in this paper consists in constructing a finite complete prefix of the unfolding of the given contextual net, that is a finite prefix in which all the markings that are reachable from the initial marking are present, and in searching in each branch of this prefix for the goal marking by solving an appropriate linear programming problem.

5

Clusters, Confusion and Unfoldings

Haar S.

Fundamenta Informaticae

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2001

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Vol. 47, nr 3,4

259-270

EN

We study independence of events in the unfoldings of Petri nets, in particular indirect influences between concurrent events: Confusion in the sense of Smith [11] and weak interference. The role of structural (conflict) clusters is investigated, and a new unfolding semantics based on clusters motivated and introduced.