Producing Enactable Protocols in Artificial Agent Societies

This paper draws upon our previous work [7, 16] in which we proposed the organisation of services around the concept of artificial agent societies and presented a framework for representing roles and protocols using LTSs. The agent would apply for a role in the society, which would result in its participation in a number of protocols. We advocated the use of the games-based metaphor for describing the protocols and presented a framework for assessing the admission of the agent to the society on the basis of its competence. In this work we look at the subsequent question: what information should the agent receive upon entry?. We can not provide it with the full protocol because of security and overload issues. Therefore, we choose to only provide the actions pertinent to the protocols that the role the agent applied for participates in the society. We employ branching bisimulation for producing a protocol equivalent to the original one with all actions not involving the role translated into silent (τ) actions. However, this approach sometimes results in non-enactable protocols. In this case, we need to repair the protocol by adding the role in question as a recipient to certain protocol messages that were causing the problems. We present three different approaches for repairing protocols, depending on the number of messages from the original protocol they modify. The modified protocol is adopted as the final one and the agent is given the role automaton that is derived from the branching bisimulation process

An incremental modular technique for checking LTL-X properties on Petri nets

Model-checking is a powerful and widespread technique for the verification of finite state concurrent systems. However, the main hindrance for wider application of this technique is the well-known state explosion problem. Modular verification is a promising natural approach to tackle this problem. It is based on the "divide and conquer" principle and aims at deducing the properties of the system from those of its components analysed in isolation. Unfortunately, several issues make the use of modular verification techniques difficult in practice. First, deciding how to partition the system into components is not trivial and can have a significant impact on the resources needed for verification. Second, when model-checking a component in isolation, how should the environment of this component be described? In this paper, we address these problems in the framework of model-checking LTL\X action-based properties on Petri nets. We propose an incremental and modular verification approach where the system model is partitioned according to the actions occurring in the property to be verified and where the environment of a component is taken into account using the linear place invariants of the system

The Object-Oriented Approach And Petri Nets For The Modelling Of Information Systems' Behaviour

This paper advocates the suitability of formalisms associating Petri nets and the object-oriented approach for systems modelling. Such formalisms have the features of good formalisms, according to the principles of software engineering, and their expressive power makes them appropriate for the modelling of distributed information systems. Namely, they enable to model a system from different points of view, and to relate these models in order to check their consistency. The first section shows the variety of models which have to be set in order to take into account all the aspects of an Information System which are considered during a project. Section II and III survey two formalisms associating Petri nets and the O-O approach - Petri Nets with Objects and Cooperative Objects - allowing to express these models and to relate them. I. SYSTEM MODELLING Any modelling approach presuppose some ideas about the nature of the system under consideration. In this paper, we see an information syst..

A Client-Server Protocol for the Composition of Petri Nets

Modelling the behavior of a system as a set of cooperating nets requires to define a high-level communication protocol which takes into account the very nature of their interactions. This paper proposes to adapt the client-server protocol promoted by the object-oriented approach to Petri nets, and to compose Petri nets according to this protocol.This protocol relies upon four basic rules which assert the honesty and discretion of clients and servers. A class of nets respecting these rules, called clientserver nets, is defined, as is the composition of these nets according to a Use function. The possibility to compose client-server nets while preserving the nets' language and liveness is studied. This possibility comes down to very simple relationships between the main characteristics of client-server nets: the demand and the confidence degree as a client, and the supply and the reliability degree as a server. These relationships are preserved by the composition of nets, so the client-s..

Cooperative Nets

: The behavior of some kinds of systems features a high rate of dynamic evolution. The system running causes the introduction of new components whereas some others disappear, and links between components are dynamically set: a component sometimes interacts with given components and sometimes with others. It is uneasy to capture such evolution inside Petri nets whose structure is fixed; but it is necessary to respect the Petri net semantics and keep the possibility to apply the structural analysis technics. The paper introduces two extensions of Petri nets dealing with this problem, Communicative Nets and Cooperative Nets. They enable to model a system as a collection of nets which encapsulate their behavior, while interacting by means of message sending or a client/ server protocol; a net may instantiate another net, and the links between nets are dynamic. An algorithm is given which captures this dynamicity by building a single fixed net whose behavior is equivalent to a whole system..

Compositional Modeling of Complex Systems: Contact Center Scenarios in OsMoSys

In this paper we present the application of a compositional modeling methodology to the re-engineering of Stochastic Well Formed net (SWN) models of a contact center. The modeling methodology is based on the definition of proper operators to connect submodels and it is supported by the OsMoSys modeling framework. The paper describes the implementation of a library of reusable SWN submodels of the contact center components and the definition of proper SWN connectors to easily develop models of different configurations of the system. We also describe the solving process of the composed models and its integration in the OsMoSys framework. Moreover, we discuss the advantages that this approach, based on the definition of classes and instances of submodels, can provide to the application of SWN to complex case studies