Jamal Bentahar

An Argumentation Framework for Communities of Web Services

As the number of Web services continues to increase, so does the opportunities to compose them to build more complex and complete business solutions. To facilitate and speed up Web-services discovery, Web services with similar (or equivalent) functionalities - such as flight booking and travel reservation - can be grouped into communities. Argumentation theory, implemented through a set of software agents that reason about Web services, can improve Web services performance through the notion of communities.

An Approach to Engineer Communities of Web Services: Concepts, architecture, operation, and deployment

This article presents an approach that provides the necessary assistance to those who are in charge of engineering communities of Web services. Current practices indicate that Web services providing the same functionality are gathered into one community, independently of their origins and the way they carry out this functionality. The provided assistance manifests itself with the concepts to use, the architecture to select, the operations to script, and the deployment to track. Two protocols frame the interactions in an environment of communities of Web services namely the Web Services Community Development Protocol and the Contract-Net Protocol. The former manages a community in terms of Web services attraction/registration/withdrawal to/with/from this community. The latter satisfies users’ needs in terms of Web services selection/contracting/triggering. Finally, the article presents a prototype illustrating the engineering approach with focus on Web services attraction.

CRM: An efficient trust and reputation model for agent computing

In open multi-agent systems, agents engage in interactions to share and exchange information. Due to the fact that these agents are self-interested, they may jeopardize mutual trust by not performing actions as they are expected to do. To this end, different models of trust have been proposed to assess the credibility of peers in the environment. These frameworks fail to consider and analyze the multiple factors impacting the trust. In this paper, we overcome this limit by proposing a comprehensive trust framework as a multi-factor model, which applies a number of measurements to evaluate the trust of interacting agents. First, this framework considers direct interactions among agents, and this part of the framework is called online trust estimation. Furthermore, after a variable interval of time, the actual performance of the evaluated agent is compared against the information provided by some other agents (consulting agents). This comparison in the off-line process leads to both adjusting the credibility of the contributing agents in trust evaluation and improving the system trust evaluation by minimizing the estimation error. What specifically distinguishes this work from the previous proposals in the same domain is its novelty in after-interaction investigation and performance analysis that prove the applicability of the proposed model in distributed multi-agent systems. In this paper, the agent structure and interaction mechanism of the proposed framework are described. A theoretical analysis of trust assessment and the system implementation along with simulations are also discussed. Finally, a comparison of our trust framework with other well-known frameworks from the literature is provided.

A taxonomy of argumentation models used for knowledge representation

Understanding argumentation and its role in human reasoning has been a continuous subject of investigation for scholars from the ancient Greek philosophers to current researchers in philosophy, logic and artificial intelligence. In recent years, argumentation models have been used in different areas such as knowledge representation, explanation, proof elaboration, commonsense reasoning, logic programming, legal reasoning, decision making, and negotiation. However, these models address quite specific needs and there is need for a conceptual framework that would organize and compare existing argumentation-based models and methods. Such a framework would be very useful especially for researchers and practitioners who want to select appropriate argumentation models or techniques to be incorporated in new software systems with argumentation capabilities. In this paper, we propose such a conceptual framework, based on taxonomy of the most important argumentation models, approaches and systems found in the literature. This framework highlights the similarities and differences between these argumentation models. As an illustration of the practical use of this framework, we present a case study which shows how we used this framework to select and enrich an argumentation model in a knowledge acquisition project which aimed at representing argumentative knowledge contained in texts critiquing military courses of action.

A Logical Model for Commitment and Argument Network for Agent Communication

In this paper we present a semantics for our approach based on social commitments (SCs) and arguments for conversational agents. More precisely, we propose a logical model based on CTL* and on dynamic logic (DL). Called Commitment and Argument Network, our formal framework based on this approach uses three basic elements: SCs, actions that agents apply to these SCs and arguments that agents use to support their actions. The advantage of this logical model is to bring together all these elements and the relations existing between them within the same framework. Our semantics makes it possible to represent the dynamics of agent communication. It also allows us to establish the important link between SCs as a deontic concept and arguments. CTL* enables us to express the temporal characteristics of SCs and arguments. DL enables us to capture the actions that agents are committed to achieve.

Reputation of Communities of Web Services - Preliminary Investigation

Web services communities can be seen as virtual clusters that agglomerate Web services with the same functionality (e.g., FlightBooking). However, selecting a community to deal with is a challenging task to users and providers. Reputation, besides other selection criteria, has been widely used for evaluating and ranking candidates. Interestingly, the definition of community reputation from the perspective of users differs from the perspective of Web service providers. In this paper, we introduce a reputation-based Web services community architecture and define some of the performance metrics that are needed to assess the reputation of a Web service community as perceived by users and providers.

Research directions in agent communication

Increasingly, software engineering involves open systems consisting of autonomous and heterogeneous participants or agents who carry out loosely coupled interactions. Accordingly, understanding and specifying communications among agents is a key concern. A focus on ways to formalize meaning distinguishes agent communication from traditional distributed computing: meaning provides a basis for flexible interactions and compliance checking. Over the years, a number of approaches have emerged with some essential and some irrelevant distinctions drawn among them. As agent abstractions gain increasing traction in the software engineering of open systems, it is important to resolve the irrelevant and highlight the essential distinctions, so that future research can be focused in the most productive directions. This article is an outcome of extensive discussions among agent communication researchers, aimed at taking stock of the field and at developing, criticizing, and refining their positions on specific approaches and future challenges. This article serves some important purposes, including identifying (1) points of broad consensus; (2) points where substantive differences remain; and (3) interesting directions of future work.

Verifying conformance of multi-agent commitment-based protocols

Although several approaches have been proposed to specify multi-agent commitment-based protocols that capture flexible and rich interactions among autonomous and heterogeneous agents, very few of them synthesize their formal specification and automatic verification in an integrated framework. In this paper, we present a new logic-based language to specify commitment-based protocols, which is derived from ACTL^*^c, a logic extending CTL^* with modalities to represent and reason about social commitments and their actions. We present a reduction technique that formally transforms the problem of model checking ACTL^*^c to the problem of model checking GCTL^* (an extension of CTL^* with action formulae). We prove that the reduction technique is sound and we fully implement it on top of the CWB-NC model checker to automatically verify the NetBill protocol, a motivated and specified example in the proposed specification language. We also apply the proposed technique to check the compliance of another protocol: the Contract Net protocol with given properties and report and discuss the obtained results. We finally develop a new symbolic algorithm to perform model checking dedicated to the proposed logic.

Verifiable semantic model for agent interactions using social commitments

Existing approaches about defining formal semantics of commitment usually consider operations as axioms or constrains on top of the commitment semantics, which fail to capture the meaning of interactions that are central to real-life business scenarios. Furthermore, existing semantic frameworks using different logics do not gather the full semantics of commitment operations and semantics of social commitments within the same framework. This paper develops a novel unified semantic model for social commitments and their operations. It proposes a logical model based on a new logic extending CTL* with commitments and operations to specify agent interactions. We also propose a new definition of assignment and delegation operations by considering the relationship between the original and new commitment contents. We prove that the proposed model satisfies some properties that are desirable when modeling agent interactions in MASs and introduce a NetBill protocol as a running example to clarify the automatic verification of this model. Finally, we present an implementation and report on experimental results of this protocol using the NuSMV and MCMAS symbolic model checkers.

Communicative commitments: Model checking and complexity analysis

We refine CTLC, a temporal logic of social commitments that extends CTL to allow reasoning about commitments agents create when communicating and their fulfillment. We present axioms of commitments and their fulfillment and provide the associated BDD-based model checking algorithms. We also analyze the time complexity of CTLC model checking in explicit models (i.e., Kripke-like structures) and its space complexity for concurrent programs, which provide compact representations. We prove that although CTLC extends CTL, their model checking algorithms still have the same time complexity for explicit models, which is P-complete with regard to the size of the model and length of the formula, and the same complexity for concurrent programs, which is PSPACE-complete with regard to the size of the components of these programs. We fully implemented the proposed algorithms on top of MCMAS, a model checker for the verification of multi-agent systems, and provide in this paper simulation results of an industrial case study.