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Search Results: 1 - 10 of 15823 matches for " Miguel Areias "
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On Combining Linear-Based Strategies for Tabled Evaluation of Logic Programs
Miguel Areias,Ricardo Rocha
Computer Science , 2011, DOI: 10.1017/S147106841100024X
Abstract: Tabled evaluation is a recognized and powerful technique that overcomes some limitations of traditional Prolog systems in dealing with recursion and redundant sub-computations. We can distinguish two main categories of tabling mechanisms: suspension-based tabling and linear tabling. While suspension-based mechanisms are considered to obtain better results in general, they have more memory space requirements and are more complex and harder to implement than linear tabling mechanisms. Arguably, the SLDT and DRA strategies are the two most successful extensions to standard linear tabled evaluation. In this work, we propose a new strategy, named DRS, and we present a framework, on top of the Yap system, that supports the combination of all these three strategies. Our implementation shares the underlying execution environment and most of the data structures used to implement tabling in Yap. We thus argue that all these common features allows us to make a first and fair comparison between these different linear tabling strategies and, therefore, better understand the advantages and weaknesses of each, when used solely or combined with the others.
Towards Multi-Threaded Local Tabling Using a Common Table Space
Miguel Areias,Ricardo Rocha
Computer Science , 2012, DOI: 10.1017/S1471068412000117
Abstract: Multi-threading is currently supported by several well-known Prolog systems providing a highly portable solution for applications that can benefit from concurrency. When multi-threading is combined with tabling, we can exploit the power of higher procedural control and declarative semantics. However, despite the availability of both threads and tabling in some Prolog systems, the implementation of these two features implies complex ties to each other and to the underlying engine. Until now, XSB was the only Prolog system combining multi-threading with tabling. In XSB, tables may be either private or shared between threads. While thread-private tables are easier to implement, shared tables have all the associated issues of locking, synchronization and potential deadlocks. In this paper, we propose an alternative view to XSB's approach. In our proposal, each thread views its tables as private but, at the engine level, we use a common table space where tables are shared among all threads. We present three designs for our common table space approach: No-Sharing (NS) (similar to XSB's private tables), Subgoal-Sharing (SS) and Full-Sharing (FS). The primary goal of this work was to reduce the memory usage for the table space but, our experimental results, using the YapTab tabling system with a local evaluation strategy, show that we can also achieve significant reductions on running time.
A Simple and Efficient Lock-Free Hash Trie Design for Concurrent Tabling
Miguel Areias,Ricardo Rocha
Computer Science , 2014,
Abstract: A critical component in the implementation of a concurrent tabling system is the design of the table space. One of the most successful proposals for representing tables is based on a two-level trie data structure, where one trie level stores the tabled subgoal calls and the other stores the computed answers. In this work, we present a simple and efficient lock-free design where both levels of the tries can be shared among threads in a concurrent environment. To implement lock-freedom we took advantage of the CAS atomic instruction that nowadays can be widely found on many common architectures. CAS reduces the granularity of the synchronization when threads access concurrent areas, but still suffers from low-level problems such as false sharing or cache memory side-effects. In order to be as effective as possible in the concurrent search and insert operations over the table space data structures, we based our design on a hash trie data structure in such a way that it minimizes potential low-level synchronization problems by dispersing as much as possible the concurrent areas. Experimental results in the Yap Prolog system show that our new lock-free hash trie design can effectively reduce the execution time and scale better than previous designs.
O score MELD revisitado
Jorge Areias
Jornal Português de Gastrenterologia , 2009,
Sociedade Portuguesa de Gastrenterologia: Resumo de Actividades (Biénio 2009 - 2011) Portuguese Society of Gastrenterology: Two Years Later
Jorge Areias
Jornal Português de Gastrenterologia , 2011,
Unbiased Multirresistance Prevalences in Real Testing Practices? An Intuitive Correcting Approach Applied to Tuberculosis in Portugal  [PDF]
Cristiana Areias, Teodoro Briz, Carla Nunes
Journal of Tuberculosis Research (JTR) , 2014, DOI: 10.4236/jtr.2014.22010
Abstract: Background: Antibiotics resistance threats Tuberculosis control, being crucial to work on unbiased MDR-TB images. The decision of testing is clinical, non-random, raising extrapolation problems. Aim: To evince and describe non-random testing practices; develop and apply a coherent and intuitive method for estimating global corrected resistance prevalences (2000-2009). Methods: A quantitative approach upon National Tuberculosis Database was undertaken, to assess testing potential predicting factors. Different factors structures in tested and non-tested cases were characterized (regarding socio-demographic and clinical variables), through binary logistic regressions. Estimated multirresistance prevalences were corrected using the essayed model. Results: Only 32% of cases had been tested, where MDR-TB prevalence was 2.38%. All factors influenced the practice of testing (p < 0.05). Corrected resistance estimates in non-tested ranged 1.96% - 2.71%, and the global weighted average found ranged 2.07% - 2.51%, depending on the chosen strata structure. Conclusions: MDR-TB prevalence representation must consider patients’ characteristics influencing testing. The correction method improved prevalences interpretation substantially; corrected and conventional values were close, because tested and non-tested had similar structures. But in other settings or health problems, correcting such estimates can make a relevant difference.
Hepatite B Crónica
Teresa Moreira,Jorge Areias
Jornal Português de Gastrenterologia , 2009,
O MEC e a reorganiza??o curricular
S?o Paulo em Perspectiva , 2000, DOI: 10.1590/S0102-88392000000100011
Abstract: o texto apresenta um resumo sobre o movimento de reorganiza??o curricular promovido pela secretaria de educa??o fundamental do ministério da educa??o do brasil e aborda os seguintes temas, entre outros: organiza??o da educa??o básica; quest?o curricular e qualidade da educa??o; parametros curriculares nacionais; referências curriculares e concep??es norteadoras; e forma??o de professores.
Implementa o do Programa Saúde da Família Indígena no estado de Mato Grosso do Sul
Marco Aurélio de Camargo Areias
Saúde Coletiva , 2009,
Abstract: La implementación del Programa de Salud Familiar Indígena en el estado de Mato Grosso do Sul, Brasil, en sociedad con la FUNASA y una Organización No Governamentable, reveló aumento inicial en el gasto con medicinas, equipamientos y materiales y reducción drástica posterior, ademas de la contratatación de personas, que tuve un crecimiento de 283%. Los coeficientes de nacimiento y fertilidad se extendieron en 39% y 55% respectivamente. El crecimiento demográfico fue de 22%. No tuve muertes maternales entre 2002 y 2004. El prenatal aumentó 3.5 veces en Jaguapirú, 6 veces en la comunidad Bororó, con una reducción de abortos registrados. La colecta de colpocitologia oncótica empezó en 2003 y aumentó 4 y 2.5 veces en los dos pueblos, respectivamente.
GE - Jornal Português de Gastrenterologia, 2009 - 2011
Rui Tato Marinho,Jorge Areias,Isabelle Cremers
Jornal Português de Gastrenterologia , 2009,
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