Letizia Leonardi

MARS: a programmable coordination architecture for mobile agents

Mobile agents offer much promise, but agent mobility and Internet openness make coordination more difficult. Mobile Agent Reactive Spaces (MARS), a Linda-like coordination architecture with programming features, can handle a heterogeneous network while still allowing simple and flexible application design.

Mobile-agent coordination models for Internet applications

Internet applications face challenges that mobile agents and the adoption of enhanced coordination models may overcome. Each year more applications shift from intranets to the Internet, and Internet-oriented applications become more popular. New design and programming paradigms call help harness the Webs potential. Traditional distributed applications assign a set of processes to a given execution environment that, acting as local-resource managers, cooperating a network-unaware fashion. In contrast, the mobile-agent paradigm defines applications as consisting of network-aware entities-agents-which can exhibit mobility by actively changing their execution environment, transferring themselves during execution. The authors propose a taxonomy of possible coordination models for mobile-agent applications, then use their taxonomy to survey and analyze resent mobile-agent coordination proposals. Their case study, which focuses on a Web-based information-retrieval application, helps show that the mobility of application components and the distribution areas breadth can create coordination problems different from those encountered in traditional distributed applications.

Reactive Tuple Spaces for Mobile Agent Coordination

The paper surveys several coordination models for mobile agent applications and outlines the advantages of uncoupled coordination models based on reactive blackboards. On this base, the paper presents the design and the implementation of the MARS system, a coordination tool for Java-based mobile agents. MARS defines Linda-like tuple spaces that can be programmed to react with specific actions to the accesses made by mobile agents.

Diffusive load-balancing policies for dynamic applications

To evaluate a set of local dynamic load-balancing strategies inspired by diffusion and characterized by different scopes of locality, the authors compare the effect of application dynamicity on performance. The algorithms used achieve the load balancing goal by only using load information belonging to a restricted space and by composing independent local actions.

Engineering mobile agent applications via context-dependent coordination

Mobility introduces peculiar coordination problems in agent-based Internet applications. First, it suggests the exploitation of an infrastructure based on a multiplicity of local interaction spaces. Second, it may require coordination activities to be adapted both to the characteristics of the execution environment where they occur and to the needs of the application to which the coordinating agents belong. This paper introduces the concept of context-dependent coordination based on programmable interaction spaces. On the one hand, interaction spaces associated to different execution environments may be independently programmed so as to lead to differentiated, environment-dependent, behaviors. On the other hand, agents can program the interaction spaces of the visited execution environments to obtain an application-dependent behavior of the interaction spaces themselves. Several examples show how an infrastructure for context-dependent coordination can be exploited to simplify the design of Internet applications based on mobile agents. In addition, the MARS coordination infrastructure is presented as an example of a system in which the concept of context-dependent coordination has found a clean and efficient implementation.

Cofields: a physically inspired approach to motion coordination

As computing becomes increasingly pervasive, autonomous computers are going to be embedded in everyday objects in our physical environment. In such scenarios, mobility itself will be pervasive. Mobile users, mobile devices, computer-enabled vehicles, and mobile software components will define a dynamic, networked world in which a large set of autonomous components will interact with each other to orchestrate their activities. We focus on the problem of coordinating autonomous agents movements in a distributed environment. Orchestrating mobile autonomous agents can take inspiration from the laws of physics. Agents movements could be driven by locally perceived computational force fields, or cofields, generated by the agents themselves and propagated through an embedded infrastructure.

Supporting cooperative WWW browsing: a proxy-based approach

The paper presents a system for synchronous cooperative browsing that permits users within a workgroup to share information and cooperate toward a common goal. The system implementation is based on a Java proxy, to achieve portability without requiring modification neither to browsers nor to servers. In addition, the paper shows that the implemented system defines a general framework for interactive multi-user WWW applications.

BRAIN: A Framework for Flexible Role-Based Interactions in Multiagent Systems

Agent-based approaches in application development seem to meet the requirements of adaptability, scalability, decentralization, and flexibility imposed by complex software systems. In open applications, interactions among agents are one of the most important issues that must be faced carefully. In this paper we propose the BRAIN framework, which aims at supporting the different phases of the development of interactions in agent-based applications, relying on the concept of role to model agent interactions. Roles carry different advantages in modeling interactions and, consequently, in exploiting derived infrastructures to support multiagent systems. Besides the interaction model, the BRAIN framework includes XRole, an XML-based notation to express roles in an interoperable way, and Rolesystem, an interaction infrastructure that implements the proposed model. An application example shows the advantages of our approach in application engineering.

Co-fields: towards a unifying approach to the engineering of swarm intelligent systems

Swarm intelligent systems, in which the paths to problem solving emerge as the result of interactions between simple autonomous components (agents or ants) and between them and their environment, appear very promising to develop robust and flexible software application. However, the variety of swarm-based approaches that have been proposed so far still lacks a common modeling and engineering methodology. In the attempt to overcome this problem, this paper presents a general coordination methodology in which swarms components are simply driven by abstract computational force fields (Co-Fields), generated either by agents, or by the environment. By having agents be driven in their activities by such fields, globally coordinated behaviors can naturally emerge. Although this model still does not offer a complete engineering methodology, it can provide a unifying abstraction for swarm intelligent systems and it can also be exploited to formalize these systems in terms of dynamical systems whose behavior can be described via differential equations. Several example of swarm systems modeled with Co-Fields are presented to support our thesis.

On Self-Adaptation, Self-Expression, and Self-Awareness in Autonomic Service Component Ensembles

Software systems operating in open-ended and unpredictable environments have to become autonomic, i.e., capable of dynamically adapting their behavior in response to changing situations. To this end, key research issues include: (i) framing the schemes that can facilitate components (or ensembles of) to exhibit self-adaptive behaviors, (ii) identifying mechanisms to enable components or ensembles to self-express the most suitable adaptation scheme, and (iii) acquiring the proper degree of self-awareness to enable putting in action self-adaptation and self-expression schemes. In this position paper, with the help of a representative case study, we frame and discuss the above issues, survey the state of the art in the area, and sketch the main research challenges that will be faced in the ASCENS project towards the definition of a fully-fledged framework for autonomic services.