Computer Science

Logic programming provides a high-level view of programming, giving implementers a vast latitude into what techniques to explore to achieve the best performance for logic programs. Towards obtaining maximum performance, one of the holy grails of logic programming has been to design computational models that could be executed efficiently and that would allow both for a reduction of the search space and for exploiting all the available parallelism in the application. These goals have motivated the design of the Extended Andorra Model, a model where goals that do not constrain non-deterministic goals can execute first.
In this work we present and evaluate the Basic design for Extended Andorra Model (BEAM), a system that builds upon David H. D. Warren's original EAM with Implicit Control. We provide a complete description and implementation of the BEAM System as a set of rewrite and control rules. We present the major data structures and execution algorithms that are required for efficient execution, and evaluate system performance.
A detailed performance study of our system is included. Our results show that the system achieves acceptable base performance, and that a number of applications benefit from the advanced search inherent to the EAM.

Abstract. Mobile agents are the latest software technology to program flexible and efficient distributed applications, since they are independent programs that travel over the network, focusing on local communication, rather than the usual communication paradigms. Most current systems implement semantics that are hard if not impossible to prove correct.

This paper presents DAOS, a model for exploitation of And-and Or-parallelism in logic programs. DAOS assumes a physically distributed memory environment and a logically shared address space. Exploiting both major forms of implicit parallelism should serve a broadest range of applications. Besides, a model that uses a distributed memory environment provides scalability and can be implemented over a computer network.

Abstract We propose a programming model for distributed concurrent systems with mobile objects in the context of a process calculus. Code mobility is induced by lexical scoping on names. Objects and messages migrate towards the site where their prefies are lexically bound. Class definitions, on the other hand, are downloadedfrom the site where they are defined, and are instantiated locally upon arrival. We provide several programming examples to demonstrate the expressiveness of the model.

Abstract—We address the problem of integrating real-time fault-tolerance mechanisms into peer-to-peer systems, with specific architecture and deployment constraints. For this purpose we implemented a prototype hierarchical peer-to-peer framework in which the leaf peers are sensors that generate different kinds of traffic such as mesh management, events, video and audio. We evaluate the framework by measuring packet loss, response time, jitter and mesh overhead for each type of traffic under peer failure.

Abstract We give a speci cation for an abstract machine for object calculi. The instruction set is intended to work as a target assembly language to which high level concurrent languages may be compiled. As a case example the compilation of the TyCO object calculus is treated. Some preliminary results on a prototype implementation are given. Keywords: Object, Concurrency, Abstract-Machine, Language, Implementation.

Resumo Um ambiente hospitalar pervasivo necessita que as entidades presente neste contexto (como pessoas e equipamentos) estejam em perfeita sincronia para a realização das tarefas médicas comuns no seu dia-a-dia. Uma das maneiras mais indicada para efetuar a representação deste domínio é através de ontologias. Desta forma, este trabalho tem como principal objetivo mostrar o processo de desenvolvimento de uma ferramenta para o processamento de ontologias em ambientes pervasivos hospitalares.

Abstract. We present an architecture that allows the seamless configuration of computer labs to work as dedicated computing clusters during periods of user inactivity. The operation of the cluster is fully automated by making use of differentiated network booting and a job management system. We have prepared it to be plugged to a larger computational grid. We provide some preliminary performance results obtained.

Abstract In this paper we present an universal methodology for finding all the occurrences of a given set of subgraphs in one single larger graph. Past approaches would either enumerate all possible subgraphs of a certain size or query a single subgraph. We use g-tries, a data structure specialized in dealing with subgraph sets. G-Tries store the topological information on a tree that exposes common substructure.

One of the major problems that actual logic programming systems have to address is whether and how to prune undesirable parts of the search space. A region of the search space would definitely be undesirable if it can only repeat previously found solutions, or if it is well-known that the whole computation will fail. Or it may be the case that we are interested in a subset of solutions. In this work we discuss how the BEAM addresses pruning issues.

Abstract Despite extensive theoretical work on process-calculi, abstract machine speci cations and implementations of actual computational models are still scarce. Moreover, a general framework for compiling languages based on these calculi is still elusive. We propose a core assembly language onto which process-calculi based languages may be compiled and present a speci cation for a self-contained abstract machine that runs this assembly code.

Abstract: Currently, Pervasive Computing has focused on the development of programmable and interactive environments, which are intended to help the user in daily activities. The health system of the future envisages the use of Pervasive Computing as a way of optimizing and automating clinical activities.