Mobile agents represent a promising technology for the development of Internet applications. However, mobile computational entities introduce peculiar problems w.r.t. the coordination of the application components. The paper outlines the advantages of Linda-like coordination models, and shows how a programmable coordination model based on reactive tuple spaces can provide further desirable features for Internet applications based on mobile agents. Accordingly, the paper presents the design and the implementation of the MARS coordination architecture for Java-based mobile agents. MARS defines Linda-like tuple spaces, which can be programmed to react with specific actions to the accesses made by mobile agents.

Mobile active computational entities introduce peculiar problems in the coordination of distributed application components. 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. Keywords: Mobile Agents, Coordination, Reactive Tuple Spaces, Java, WWW Information Retrieval 1. Introduction Traditional distributed applications are designed as a set of processes statically assigned to given execution environments and cooperating in a (mostly) network-unaware fashion [Adl95]. The mobile agent paradigm, instead, defines applications composed by network-aware entities (agents) capable of changing their execution env...

Abstract—The original Web did not support multiuser, interactive applications. This shortcoming is being studied, and several approaches have been proposed to use the Web as a platform for programming Internet applications. However, most existing approaches are oriented to centralized applications at servers, or local programs within clients. To overcome this deficit, we introduce PageSpace, that is a reference architecture for designing interactive multiagent applications. In this paper we describe how we control agents in PageSpace, using variants of the coordination language Linda to guide their interactions. Coordination technology is integrated with the standard Web technology and the programming language Java. Several kinds of agents live in the PageSpace: user interface agents, personal homeagents, agents that implement applications, and agents which interoperate with legacy systems. Within our architecture, it is possible to support fault-tolerance and mobile agents as well.

. Coordination models for closed concurrent systems like Linda and Gamma have been well established during the last few years. Closed systems typically are planned ahead and consist only of active components the behaviour of which is known in advance. In contrast, open systems are inherently heterogeneous and dynamically change their configuration over time. Models for coordinating software agents in open systems must therefore be able to cope with constantly changing configurations and new, unknown kinds of agents. In this paper, we identify the requirements of open systems with respect to coordination models and develop a coordination model suitable for these purposes. 1 Introduction Open systems are systems in which new active entities (usually called "objects", "agents", or "actors") may dynamically join and later leave, i.e. evolving self-- organizing systems of interacting intelligent agents [2, 10]. More precisely, open systems can be defined as being composed of software compo...

A new approach to support the development of distributed software systems is outlined. As far as static aspects are concerned, standard object-oriented design methods are used. Dynamic aspects like status of services or resource handling in objects and methods, however, play the key role in distributed systems. The main contribution of the approach is a method which puts the focus on these aspects right from the beginning of a design. A new formalism based on extended Petri-Nets -- so called Object Coordination Nets (OCoNs) -- is used to describe the behavior of an object on a per method basis and for the usage of object resources. The formalism is integrated into higher levels of object-oriented design as an additional means to describe dynamic behavior. Integration with a standard sequential object-oriented language like C++ is used to organize method nets in a class context. This provides a type system for the nets as well. The sequential language can be interpreted as filling the c...

The paper presents a new reflective model, called Channel Reification, which can be used in distributed computations to overcome difficulties experienced by other models in the literature when monitoring communication among objects. The channel is an extension of the message reification model. A Channel is a communication manager incarning successive messages exchanges by two objects: its application range between those of message reification and those of meta-object model. After a brief review of existing reflective models and how reflections can be used in distributed systems, channel reification is presented and compared to the widely used meta-object model. Applications of channel reification to protocol implementation, and to fault tolerant object systems are shown. Future extensions to this model are also summarized. Keyword: Object-Oriented, Computational Reflection, Reflective Distributed Systems. I. Introduction In the development of complex distributed applications, two co...

. The paper proposes a formal approach to building software performance models for distributed and/or concurrent software systems from a description of the system's architecture by using graph transformations. The performance model is based on the Layered Queueing Network (LQN) formalism, an extension of the well-known Queueing Network modelling technique [16, 17, 8]. The transformation from the architectural description of a given system to its LQN model is based on PROGRES, a known visual language and environment for programming with graph rewriting systems [9-11]. The transformation result is an LQN model that can be analysed with existent solvers [5]. 1 Introduction It is generally accepted that performance characteristics, such as response time and throughput, play an important role in defining the quality of software products. In order to meet the performance requirements of such systems, the software developers should be able to assess and understand the effect of various desig...

The paper addresses the issue of coordination in distributed applications based on mobile agents. The presence of mobile active computational entities makes traditional coordination models based on message-passing, such as the client-server one, not effective, from both the performance and the usability points of view. Indirect coordination models suit better the mobile scenario: interactions occur via blackboards where information is accessed in an associative way, thus uncoupling the involved entities. The paper surveys these different approaches and evaluates their impact in the design of a widely distributed application in the area of information retrieval. This permits to outline the advantages of uncoupled coordination models and to point out the urge for a coordination model based on reactive and programmable blackboards, that may increase the safety and the security of the environment while simplifying the task of programming distributed mobile agent applications. Keywords: Di...

The paper introduces a taxonomy of the possible coordination models for mobile agent applications and evaluates their impact in the design of a widely distributed application in the area of information retrieval. The analysis outlines the advantages of uncoupled coordination models and points out the need for coordination models based on reactive blackboards. 1. Introduction Traditional distributed applications are designed as a set of processes assigned to a given execution environment that cooperate in a (mostly) networkunaware fashion [2]. Instead, the mobile agent paradigm defines applications composed by network-aware entities (agents) capable of actively changing their execution environment by transferring themselves while executing (mobility) [10]. The shift to the mobile agent paradigm is widely justified by the advantages it provides over traditional approaches in widely distributed applications [3, 14]: (i) mobile agents can dramatically save bandwidth, by moving to the res...

This paper discusses software reusability strategies for performance and reliability modeling tools. Special emphasis is on webembedded tools, and the potential interaction between such tools. We present the system analysis tools (SAT) application programming interface, which allows for quickly embedding existing tools in the web, and generally simplifies programming analysis tools by structured reuse. We also