Christophe Sibertin-Blanc

Protocol Moderators as Active Middle-Agents in Multi-Agent Systems

Interaction protocols are widely recognized as an essential mechanism for coordination within multi-agent systems. There is thus a need for coordination models for specifying, validating, and implementing protocols, possibly open and concurrent, efficiently and reliably. This paper proposes such a model, which considers protocols as resources and each conversation among agents following the rules of a protocol as a well-identified process. To this end, a new kind of middle-agent, called Moderator, is introduced. A Moderator is in charge of monitoring a conversation so that it progresses according to the protocol rules, and provides agents with services to ease their involvement in the conversation. This model fits the organization-centered view of multi-agent systems as it strictly distinguishes the agent-level and the organization-level concerns with regard to interaction. In addition, the paper shows that this model is supported by a High-Level Petri Net language that covers all the steps of protocol engineering: design, validation, implementation. This paper presents this Moderator Coordination Model along four related dimensions: a conceptual model of protocols, a MAS architecture, a suitable modeling formalism, and an associated development process.

CoOperative objects: principles, use and implementation

It is no longer relevant to praise the qualities of the Object-Oriented Approach and the Petri Net Theory. Each of them has proved to be a powerful framework in its field of application. However it is a challenge to associate them into a conceptual framework which combines the expressive power of both approaches while maintaining their respective merits. Moreover, it must be shown that such a formalism can be implemented in a sound and efficient manner. This paper is a comprehensive presentation of the CoOperative Objects formalism. This formalism embraces the theoretical and pragmatic features of both the Petri net and the Object-Oriented approaches by thoroughly integrating their concepts. It is as well-adapted to the specification and the validation of open distributed systems as to their implementation. The basic idea is that a Petri net processes data objects as tokens, while the behaviour of an active object is defined by a Petri net. This paper also proposes a CoOperative Object solution to the dynamic dining philosophers problem, and tackles implementation issues through the presentation of SYROCO, a CoOperative Objects compiler.

Design of User-Driven Interfaces Using Petri Nets and Objects

This paper presents a survey of three formalisms that are used for modelling the dialogue of user-driven interfaces: state diagrams, events and Petri nets. Petri nets are found to be the best suited formalism in this area, even if they lack structure. In order to address this problem, the usefulness of the object-oriented approach is discussed, and we present a formalism, called Petri Nets with Objects (PNO), that integrates both object-oriented and Petri nets approaches. A three-step method for building such models, consisting in defining the object classes, definiting the presentation and modelling the applications dialogue, is presented, and a detailed example illustrates the application of this method. Finally, we present an overview of the benefits that can be expected from the use of the PNO formalism in dialogue modelling.

Inter-organizational workflows for enterprise coordination

Workflow systems are widely adopted by organizations for supporting business processes. In particular, workflow systems help organizations to coordinate the different actors involved in the business process by automating repetitive tasks and facilitating the distribution of documents, information, and control. Today’s workflow systems however do not adequately support processes that cross the boundaries of multiple organizations. The enhancement of workflow systems in this direction, Inter-Organizational Workflows (IOWs), is essential given the growing need for organizations to cooperate and coordinate their activities in order to meet the new demands of highly dynamic markets. This paper starts by describing some of the issues related to the collaboration among organizations, pointing out a number of factors that can impact on the required support. After having introduced the basic terminology of traditional workflow and workflow systems, the chapter outlines some requirements for 10W, distinguishing between loose and tight IOW. Loose IOWs refer to occasional cooperation, free of structural constraints, where neither the involved partners nor their relationships are defined a priori. Tight IOWs refer to a structural cooperation among organizations, i.e., a cooperation based on a well-established infrastructure among pre-defined partners. Based on this distinction and the related requirements, the chapter presents two approaches to the design and the implementation of IOWs. The first approach adopts the notion of software agents for enhancing workflow systems and allowing their use in loose IOWs. The second approach, which can be supported by an agent based implementation, combines Petri Nets and Federated Databases for providing the more structured support needed by tight IOWs. Both approaches are compliant with the Workflow Management Coalition reference architecture. This guarantees the possibility to tailor the support provided by the IOW to the needs of the collaborating organizations, remaining within a coherent framework of reference.

The hurried philosophers

The purpose of this case study is to test the expressive and analytic power of languages merging Petri nets and concepts of the Object-Oriented approach. Regarding the expressive power, the main tested features are: - local control: each object plays its own Petri net, without regard to the state of other objects; - dynamic instantiation: while the system is running, new objects may appear and some may disappear; - dynamic binding: the partner of a communication is defined when the communication occurs, and not by the model (or at “compile time”); - inheritance and polymorphism: a class may inherit some features from other classes, and a communication happens according to the actual class of the partner.

Impact of Tenacity upon the Behaviors of Social Actors

The Sociology of the Organized Actions is a well-established theory that focuses upon the actual behaviors of the members of social organizations, and reveals the (to a large extent implicit) motives of social actors. The formalization of this theory leads to model the structure of an organization as a social game, including the Prisoners’ Dilemma as a specific case. In order to perform simulations of social organizations modeled in this way, the SocLab environment contains an algorithm allowing the model’s actors to play the social game and so to determine how they could cooperate with each other. This algorithm includes several parameters, and we study the influence of one of them, the Tenacity.

Ambiguity and structural properties of basic sequence diagrams

Sequence Diagrams (SDs) are one of the most popular elements of the UML notation to model the dynamics of systems. However, the graphical representation of basic SDs suffers from an inherent ambiguity that has led to different definitions in UML 1.x and in UML 2.0. This ambiguity paves the way for the consideration of several semantics for basic SDs. The paper studies four of these semantics and shows to what extent their differences for a given SD (that is the amount of ambiguity of this diagram) comes from its structural properties (linearity, local control and local causality). The fulfilment of these properties can serve as a measure of the ambiguity of a SD, and thus the attention to be paid at its validation.

The MAELIA Multi-Agent Platform for Integrated Analysis of Interactions Between Agricultural Land-Use and Low-Water Management Strategies

The MAELIA project is developing an agent-based modeling and simulation platform to study the environmental, economic and social impacts of various regulations regarding water use and water management in combination with climate change. It is applied to the case of the French Adour-Garonne Basin, which is the most concerned in France by water scarcity during the low-water period. An integrated approach has been chosen to model this social-ecological system: the model combines spatiotemporal models of ecologic (e.g. rainfall and temperature changes, water flow and plant growth) and socio-economic (e.g. farmer decision-making process, management of low-water flow, demography, land use and land cover changes) processes and sub-models of cognitive sharing among agents (e.g. weather forecast, normative constraints on behaviors)

Using Soclab for a Rigorous Assessment of the Social Feasibility of Agricultural Policies

This paper presents a theoretical and methodological framework to take into consideration the social dimension in a sustainable development project. To do this, the authors have developed the SocLab software environment, which implements a formalization of a well-established sociological theory, and enables the modeling of social organizations, to analyze their properties and to simulate social actors’ behaviors. SocLab was used to assess the social acceptability of new agricultural practices more in line with the preservation of water resources and natural environments, in a well defined context. The paper shows how it was used and presents the main results.

A Collaborative Information System Architecture for Process-Based Crisis Management

In computer-based crisis management, participating actors have to put in common their information systems (IS). One of the main issues they have to face is to interoperate and coordinate these ISs in order to ease their collaborations and take the right decisions at the right moment. For that, they have to set up a Collaborative Information System (CIS) for orchestrating a Collaborative Process (CP) whose activities are performed by the participating ISs. The aim of this paper is to define the functional requirements of such a CIS and then to propose a conceptual architecture meeting these requirements. This architecture supports a perception-decision-action iteration for crisis reduction. Indeed, it provides means to capture information about the impacted real world, to support the definition and the adaptation of the CP managing the crisis reduction, and to coordinate and assign to each participant the actions to be undertaken. These actions modify the real world and lead to perform a new iteration until the crisis resolution.