Abstract
In this paper, we study the relationship between tabulation and goal-oriented bottom-up evaluation of logic programs, Differences emerge when one tries to identify features of one evaluation method in the other. We show that to obtain the same effect as tabulation in top-down evaluation, one has to perform a careful adomment in programs to be evaluated bottom-up. Furthermore, we propose an efficient algorithm to perform forward subsumption checking over adorned magic facts. (C) Elsevier Science Inc., 1997.

Abstract
Current data abstraction mechanisms are not adequate to control sharing of state in the general case involving objects in linked structures. The pervading possibility of sharing is a source of errors and an obstacle to language implementation techniques. We present a general extension to programming languages which makes the ability to share state a first class property of a data type, resolving a long-standing flaw in existing data abstraction mechanisms. Balloon types enforce a strong form of encapsulation: no state reachable (directly or transitively) by a balloon object is referenced by any external object. Syntactic simplicity is achieved by relying on a non-trivial static analysis as the checking mechanism. Balloon types are applicable in a wide range of areas such as program transformation, memory management and distributed systems. They are the key to obtaining self-contained composite objects, truly opaque data abstractions and value types-important concepts for the development of large scale, provably correct programs. © Springer-Verlag Berhn Heidelberg 1997.

Abstract
This paper is concerned with the formalization of a automated contracting mechanism that enables a society of cooperative resource allocation agents to negotiate rationally in a self-interested meta-society. Such environments induce agents to adopt different social behaviors according to the negotiation partner. This problem may be solved by taking an economic perspective in all the decisions, namely, by using utility based agents, through the use of marginal utility calculations, and defining dynamically the market extent for a task. The risk attitude and reactivity of each agent can be parameterized in order to achieve different negotiation strategies. The framework presented in this paper can be applied in a wide variety of situations, ranging from electronic commerce on virtual economic markets, to load distribution problems. © Springer-Verlag Berlin Heidelberg 1997.

Abstract
Load distribution is a well known critical problem in every distributed system. From operating systems to agent oriented applications it is not difficult to find cases where processing nodes are overloaded when, at the same time, other peers present low levels of activity. In agent oriented applications, where the appeal to cooperation is almost a constant event, these unbalanced situations may generate serious cases of contention, deadlock or simply large idle times. The implementation of load distribution strategies in a distributed system may help significantly to improve its overall performance and reduce effectively such undesirable situations. In order to study the effects of different load distribution policies in agent based applications a generic load distribution simulation system was design and implemented. The system allows the specification of multiorganisational distributed systems with dynamic load patterns. Its main characteristics and functionalities are presented in this paper.

Abstract
This paper presents and discusses the design and the development of a pattern recognition agent based on neural networks. This agent is part of an intelligent navigation system, providing it with the necessary vision abilities so that it can be placed on a strange environment in order to explore and recognise its structures and specificities. Although similar, the properties of the recognised objects change through time and according to each specific environment. The flexibility required by such recognition process was implemented by several pattern recognition agents. Each agent is based on a neural network and can be trained on-line by a parallel training algorithm to allow an effective real time utilisation.

Abstract
This article presents an evaluation study of point-to-point and collective communication performance on a parallel processing system, a 16 node Parsytec PowerXplorer, using three different communication environments: PARIX, PVM and MPI.