Scielo RSS <![CDATA[Journal of the Brazilian Computer Society]]> http://www.scielo.br/rss.php?pid=0104-650020070004&lang=en vol. 13 num. 4 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[<B>Letter from the editor-in-chief</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-65002007000400001&lng=en&nrm=iso&tlng=en <![CDATA[<B>Regularized implicit surface reconstruction from points and normals</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-65002007000400002&lng=en&nrm=iso&tlng=en We consider the problem of surface reconstruction of a geometric object from a finite set of sample points with normals. Our contribution is to present a new scheme for implicit surface reconstruction. Similarly to the multilevel partition of unity (MPU) method we hierarchically divide the domain obtaining local approximation for the object on each part, and then patch all together obtaining a global description of the object. Our new scheme uses ridge regression and weighted gradient one fitting techniques to get better stability on local approximations. The method behaves reasonably on sparse set of points and data with holes as those which comes from 3D scanning of real objects. <![CDATA[<B>Model-based evolution of collaborative agent-based systems</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-65002007000400003&lng=en&nrm=iso&tlng=en As demands for behaviorally sophisticated software grow, agent-based systems are increasingly being employed. Software agents are frequently applied to large, complex systems that involve interdisciplinary development teams. These complex systems have proved to be challenging to develop and evolve, even for the most competent software engineers. Taking lessons learned in other engineering disciplines such as computer and architectural engineering we investigated a model-based engineering approach called Model-Driven Architecture (MDA) to automate, whenever possible, the development and evolution of agent-based applications. In our investigation, we use the Cognitive Agent Architecture (Cougaar); one of the most mature and sophisticated collaborative agent-based architectures. MDA and Cougaar served as the primary components and implementation platform for our research. In this paper we present our approach and demonstrate how MDA is effective for producing sophisticated agent-based systems. A key challenge was found in designing a flexible meta-model framework that would accommodate both top-down domain information and bottom-up platform specific constructs, as well as the transformations and mappings between them. We employed a General Domain Application Model (GDAM) as the platform-independent model layer and General Cougaar Application Model (GCAM) layer as the platform specific model respectively. Domain-level requirements are formulated using a XML Process Definition Language (XPDL) based graphical editor and are the refined through a series of model transformations (via the underlying metamodel) to systematically generate the agent-based software system. Through an illustrative case-study, we report on the feasibility, strengths and limitations of the model-based approach as it was investigated with the Cougaar. <![CDATA[<B>Evolutionary TBL template generation</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-65002007000400004&lng=en&nrm=iso&tlng=en Transformation Based Learning (TBL) is a Machine Learning technique frequently used in some Natural Language Processing (NLP) tasks. TBL uses rule templates to identify error-correcting patterns. A critical requirement in TBL is the availability of a problem domain expert to build these rule templates. In this work, we propose an evolutionary approach based on Genetic Algorithms to automatically implement the template generation process. Additionally, we report our findings on five experiments with useful NLP tasks. We observe that our approach provides template sets with a mean loss of performance of 0.5% when compared to human built templates <![CDATA[<B>Formal specification and verification of real-time systems using Graph Grammars</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-65002007000400005&lng=en&nrm=iso&tlng=en The importance of real-time systems has enormously increased in the last decade. Application areas that typically need real-time models include railroad systems, intelligent vehicle highway systems, avionics, multimedia and telephony. To assure that such systems are correct, additionally to prove that they provide the required functionality, time constraints must be satisfied. There are already formal specification methods for real-time systems, but most of them are difficult to use by software developers, that are usually not very familiar with mathematical notation but rather specify systems using the object-oriented paradigm. In this paper we propose a formal approach to specify and analyze real-time systems that has an object-oriented flavor. This approach is based on Object-Based Graph Grammars (OBGGs), a formal description technique suitable for the specification of asynchronous distributed systems, and intuitive even for non-theoreticians. We extend OBGGs to enable explicit modeling of time constraints, and define the semantics of the specifications via transition systems. Finally, we translate timed OBGGs to Timed Automata, a formal notation that is wide spread in the area of real-time systems modeling and allows the automatic verification of properties. <![CDATA[<B>Localization and mapping in urban environments using mobile robots</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-65002007000400006&lng=en&nrm=iso&tlng=en Mapping is a basic capability for mobile robots. Most applications demand some level of knowledge about the environment to be accomplished. Most mapping approaches in the literature are designed to perform in small structured (indoor) environments. This paper addresses the problems of localization and mapping in large urban (outdoor) environments. Due to their complexity, lack of structure and dimensions, urban environments presents several difficulties for the mapping task. Our approach has been extensively tested and validated in realistic situations. Our experimental results include maps of several city blocks and a performance analysis of the algorithms proposed. <![CDATA[<B>Modularizing communication middleware concerns using aspects</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-65002007000400007&lng=en&nrm=iso&tlng=en Software engineers often rely on communication middleware platforms to design and implement distributed systems. However, middleware functionality is usually invasive, pervasive and tangled with business-specific concerns. In this paper, we describe an aspect-oriented distributed programming system that encapsulates middleware services provided by Java RMI and Java IDL. The proposed system, called DAJ, handles the basic service provided by such object-oriented middleware platforms, i.e., synchronous remote calls using call by-serialization and call by-remote-reference semantics. The paper documents our experience in using DAJ to modularize middleware concerns from three legacy distributed systems.