In this paper we present sofar, a versatile multi-agent framework designed for Distributed Information Management tasks. sofar embraces the notion of proactivity as the opportunistic reuse of the services provided by other agents, and provides the means to enable agents to locate suitable service providers. The contribution of sofar is to combine some ideas from the distributed computing community with the performative-based communications used in other agent systems: communications in sofar are based on the startpoint/endpoint paradigm, which is the foundation of Nexus, the communication layer at the heart of the Computational Grid. We explain the rationale behind our design decisions, and describe the predefined set of agents which make up the core of the system. Two distributed information management applications have been written, a general query architecture and an open hypermedia application, and we recount their design and operations.

We have recently defined a new algorithm for distributed garbage collection based on reference-counting [20, 24]. At the heart of the algorithm, we find tree rerooting, a mechanism able to reduce third-party dependencies by reorganising diffusion trees. In reality, the algorithm describes a spectrum of algorithms according to the policy used to manage messages. In this paper, we present the implementation of the algorithm and evaluate its performance. We have implemented two policies, which are extremes of the spectrum, respectively using and not using tree rerooting. In addition, two different strategies for managing action queues have been implemented. The conclusions of our experimentations are the following. Tree rerooting offers more parallelism during distributed gc activity; we explain this phenomenon by the length reduction of causality chains in the distributed gc. Grouping messages per destination dramatically reduces the number of messages, but requires a more complex implementation as messages have to be sorted per destination. Speed up of 100% has been observed on some benchmarks.

Mobile Objects in Java provides support for object mobility in Java. Similarly to the RMI technique, a notion of client-side stub, called startpoint, is used to communicate transparently with a server-side stub, called endpoint. Objects and associated endpoints are allowed to migrate. Our approach takes care of routing method calls using an algorithm that we studied in [22]. The purpose of this paper is to present and evaluate the implementation of this algorithm in Java. In particular, two different strategies for routing method invocations are investigated, namely call forwarding and referrals. The result of our experimentation shows that the latter can be more efficient by up to 19%. 1

versatile multi-agent framework designed for Distributed Information Management tasks. SoFAR embraces the notion of proactivity as the opportunistic reuse of the services provided by other agents, and provides the means to enable agents to locate suitable service providers. The contribution of SoFAR is to combine ideas from the distributed computing community with the performative-based communications used in other agent systems: communications in SoFAR are based on the startpoint/endpoint paradigm, a powerful abstraction that can be mapped onto multiple communication layers. SoFAR also adopts an XML-based declarative approach for specifying ontologies and agents, providing a clear separation with their implementation. We explain the rationale behind our design decisions; we describe two distributed information management applications and we recount their design and operations. 1