Hamdi Yahyaoui

Toward an agent-based and context-oriented approach for Web services composition

This paper presents an agent-based and context-oriented approach that supports the composition of Web services. A Web service is an accessible application that other applications and humans can discover and invoke to satisfy multiple needs. To reduce the complexity featuring the composition of Web services, two concepts are put forward, namely, software agent and context. A software agent is an autonomous entity that acts on behalf of users and the context is any relevant information that characterizes a situation. During the composition process, software agents engage in conversations with their peers to agree on the Web services that participate in this process. Conversations between agents take into account the execution context of the Web services. The security of the computing resources on which the Web services are executed constitutes another core component of the agent-based and context-oriented approach presented in this paper.

Keyed hash function based on a chaotic map

Secure hash functions play a fundamental role in cryptographic and Web applications. They are mainly used, within digital signature schemes, to verify the integrity and authenticity of information. In this paper, we propose a simple and efficient keyed hash function based on a single chaotic map. Theoretical and simulation results demonstrate that the suggested scheme satisfies all cryptographic requirements of secure keyed hash functions such as strong confusion and diffusion capability, good collision resistance, high sensitivity to message and secret key, etc. Furthermore, it is fast and can be easily implemented through software or hardware. Moreover, the length of the hash value is flexible without any impact on the algorithm. This function is shown to have better statistical performance than many existing hash functions. Thus, the suggested hash function seems to be a good candidate as a secure keyed hash function for use in cryptographic applications.

A trust-based game theoretical model for Web services collaboration

We present in this paper a trust-based game theoretical model for Web services collaboration. Each collaboration is modeled as a game. In each round of the game, a collaborating Web service submits a cost for achieving a specific task. The task-owner Web service computes the so-called trust-based cost, which is the product between the submitted cost and the inverse of the trust value of the bidding Web service. The game winner is the Web service which has the minimal trust-based cost. The trust is derived from the quality attribute values of a Web service. These values are computed during a collaboration evaluation period. They are updated after each game round based on a demotion or promotion decision. We also show how the proposed model is convenient for modeling Web services composition and assessing the trust of composite Web services. Furthermore, we provide a metric for the assessment of the collaboration trust. The application of this metric shows that the use of the trust allows a safer collaboration with respect to a game where there is no consideration of the trust as a criteria for allocating tasks.

Towards a community-based, social network-driven framework for Web services management

This paper discusses a framework to manage Web services using the concept of community and the metaphor of social networking. On the one hand, a community gathers Web services that offer similar functionalities together. These Web services are referred to as either master or slave. On the other hand, social networking captures all interactions that occur between Web services located in the same or separate communities. Five interactions are identified and referred to as supervision, substitution, competition, collaboration, and recommendation. The mining exercise over the social networks that capture these interactions results in assigning social qualities to Web services, similar to those found in peoples daily life such as selfishness, fairness, and trustworthiness. Experiments showing the mining exercise are also reported in this paper.

A Web services composition approach based on software agents and context

We present an agent-based and context-oriented approach for Web services composition. A Web service is an accessible application that other applications and humans can discover and trigger to satisfy various needs. Due to the complexity of Web services composition, we consider two concepts to reduce this complexity: software agent and context. A software agent is an autonomous entity that acts on behalf of users, whereas context is any information relevant to characterize a situation. During composition, software agents engage conversations with their peers to agree on the Web services that will participate in the composition.

Towards a Method for Engineering Social Web Services

This paper motivates the blend of social computing with service-oriented computing, giving “birth” to social Web services. On the one hand, social computing builds user applications upon the principles of collective action and content sharing. On the other hand, service-oriented computing builds enterprise applications upon the principles of service offer and demand and loose coupling. Thanks to this blend social Web services can operate taking into account with whom they worked in the past and with whom they would like to work in the future. To engineer social Web services, this paper presents a four-step method that addresses several questions related to the engineering exercise. These questions are what relationships exist between Web services, what social networks correspond to these relationships, how to build social networks of Web services, and what social behaviors can Web services exhibit. Experiences dealing with implementing social Web services are, also, reported in the paper.

A framework to coordinate web services in composition scenarios

This paper looks into the coordination of web services following their acceptance to participate in a composition scenario. We identify two types of behaviours associated with component web services: operational and control behaviours. These behaviours are used to specify composite web services that are built upon component web services. In term of orchestration a composite web service could be either centralised or peer-to-peer. To support component/composite web services coordination per type of orchestration schema, various types of messages are exchanged between these web services. Experiments showing the use of these messages are reported in this paper as well.

Trust Assessment for Web Services Collaboration

We present in this paper a trust-based game theoretical model for Web services collaboration. The devised model is an application of the generic model about tasks allocation for agents, which is presented in [13]. We consider that a collaboration between Web services captures a possible interaction for achieving a specific task. We consider such collaboration as a game in which several Web services compete to win a task by bidding a cost for achieving it. The game winner is the Web service which has the minimal trust-based cost, which is the product of the cost and the inverse of the trust value of the bidding Web service. Initial trust values are computed based on the distance between the actual and the announced quality attribute values of a Web service. These values are computed during a collaboration evaluation period. They are updated after each game round based on a bayesian model. We show in this paper how the use of trust allows a safer collaboration between Web services with respect to collaborations where there is no consideration of the trust as a criteria for allocating tasks.

New approach for the dynamic enforcement of Web services security

We propose in this paper a new approach for the dynamic enforcement of Web services security, which is based on a synergy between Aspect-Oriented Programming (AOP) and composition of Web services. Security policies are specified as aspects. The elaborated aspects are then weaved (integrated) in the Business Process Execution Language (BPEL) process at runtime. The main contributions of our approach are threefold: (1) separating the business and security concerns of composite Web services, and hence developing them separately (2) allowing the modification of the Web service composition at run time and (3) providing modularity for modeling cross-cutting concerns between Web services. We demonstrate the feasibility of our approach by developing a Flight System (FS) that is composed of several Web services. First, a RBAC (Role Based Access Control) model for the flight system, which we called RBAC-FS, is elaborated. Afterwards, the Web services that implement the security features are developed. Finally, the BPEL aspects that integrate the security functionalities dynamically into the BPEL process are created. The devised aspects realize the elaborated RBAC-FS model and provide authentication and access control features to the flight system. Case studies and experimental results are also presented to defend our propositions.

Social Engineering of Communities of Web Services

This paper discusses the engineering of communities of Web services with emphasis on the social interactions that arise between these Web services and hence, can put some restrictions on their behaviors. Like service parks, communities gather Web services that offer similar functionalities to users. The social interactions between Web services take place within and across communities and are captured using structures known as social networks. Five types of networks are established during this engineering, which are supervision, competition, substitution, collaboration, and recommendation. Above these networks mining operations are performed, which results in assigning social attributes to Web services such as selfishness, fairness, and unpredictability. Details on the experiments are, also, reported in this paper.