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Browsing ESTG - Capítulos de livros by Field of Science and Technology (FOS) "Ciências Naturais::Ciências da Computação e da Informação"
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- Applying Scatter Search to the Location Areas ProblemPublication . Luz, Sónia Maria Almeida da; Vega-Rodríguez, Miguel A.; Gómez-Pulido, Juan A.; Sánchez-Pérez, Juan M.The Location Areas scheme is one of the most common strategies to solve the location management problem, which corresponds to the management of the mobile network configuration with the objective of minimizing the involved costs. This paper presents a new approach that uses a Scatter Search based algorithm applied to the Location Areas scheme as a cost optimization problem. With this work we pretend to analyze and set the main parameters of scatter search, using four distinct test networks and compare our results with those achieved by other authors. This is a new approach to this problem and the results obtained are very encouraging because they show that the proposed technique outperforms the existing methods in the literature.
- FlexSPMF: A Framework for Modelling and Learning Flexibility in Software ProcessesPublication . Martinho, Ricardo; Varajão, João; Domingos, DulceSoftware processes are dynamic entities that are often changed and evolved by skillful knowledge workers such as software development team members. Consequently, flexibility is one of the most important features within software process representations and related tools. However, in the everyday practice, team members do not wish for total flexibility. They rather prefer to learn about and follow previously defined advices on which, where and how they can change/adapt process representations. In this paper we present FlexSPMF: a framework for modelling controlled flexibility in software processes. It comprises three main contributions: 1) identifying a core set of flexibility concepts; 2) extending a Process Modelling Language (PML)'s metamodel with these concepts; and 3) providing modelling resources to this extended PML. This enables process engineers to define and publish software process models with additional (textual/graphical) flexibility information. Other team members can then visualise and learn about this information, and change processes accordingly.
- A Hybrid Differential Evolution Algorithm for Solving the Terminal Assignment ProblemPublication . Bernardino, Eugénia; Bernardino, Anabela; Sánchez-Pérez, Juan Manuel; Gómez-Pulido, Juan Antonio; Vega-Rodríguez, Miguel AngelThe field of communication networks has witnessed tremendous growth in recent years resulting in a large variety of combinatorial optimization problems in the design and in the management of communication networks. One of these problems is the terminal assignment problem. The task here is to assign a given set of terminals to a given set of concentrators. In this paper, we propose a Hybrid Differential Evolution Algorithm to solve the terminal assignment problem. We compare our results with the results obtained by the classical Genetic Algorithm and the Tabu Search Algorithm, widely used in literature.
- Improving Text Classification Performance with Incremental Background KnowledgePublication . Silva, Catarina; Ribeiro, BernardeteText classification is generally the process of extracting interesting and non-trivial information and knowledge from text. One of the main problems with text classification systems is the lack of labeled data, as well as the cost of labeling unlabeled data. Thus, there is a growing interest in exploring the use of unlabeled data as a way to improve classification performance in text classification. The ready availability of this kind of data in most applications makes it an appealing source of information. In this work we propose an Incremental Background Knowledge (IBK) technique to introduce unlabeled data into the training set by expanding it using initial classifiers to deliver oracle decisions. The defined incremental SVM margin-based method was tested in the Reuters-21578 benchmark showing promising results.
- Improving Visualization, Scalability and Performance of Multiclass Problems with SVM Manifold LearningPublication . Silva, Catarina; Bernardete RibeiroWe propose a learning framework to address multiclass challenges, namely visualization, scalability and performance. We focus on supervised problems by presenting an approach that uses prior information about training labels, manifold learning and support vector machines (SVMs). We employ manifold learning as a feature reduction step, nonlinearly embedding data in a low dimensional space using Isomap (Isometric Mapping), enhancing geometric characteristics and preserving the geodesic distance within the manifold. Structured SVMs are used in a multiclass setting with benefits for final multiclass classification in this reduced space. Results on a text classification toy example and on ISOLET, an isolated letter speech recognition problem, demonstrate the remarkable visualization capabilities of the method for multiclass problems in the severely reduced space, whilst improving SVMs baseline performance.
- Knowledge Extraction with Non-Negative Matrix Factorization for Text ClassificationPublication . Silva, Catarina; Ribeiro, BernardeteText classification has received increasing interest over the past decades for its wide range of applications driven by the ubiquity of textual information. The high dimensionality of those applications led to pervasive use of dimensionality reduction methods, often black-box feature extraction non-linear techniques. We show how Non-Negative Matrix Factorization (NMF), an algorithm able to learn a parts-based representation of data by imposing non-negativity constraints, can be used to represent and extract knowledge from a text classification problem. The resulting reduced set of features is tested with kernel-based machines on Reuters-21578 benchmark showing the method's performance competitiveness.
- Parameter Analysis for Differential Evolution with Pareto Tournaments in a Multiobjective Frequency Assignment ProblemPublication . Maximiano, Marisa; Vega-Rodríguez, Miguel A.; Gómez-Pulido, Juan A.; Sánchez-Pérez, Juan M.This paper presents a multiobjective approach for the Frequency Assignment Problem (FAP) in a real-world GSM network. Indeed, nowadays in GSM systems, the FAP stills continues to be a critical task for the mobile communication operators. In this work we propose a new method to address the FAP by applying the Differential Evolution (DE) algorithm in its multiobjective optimization, using the concept of Pareto Tournaments (DEPT). We present the results obtained in the tuning process of the DEPT parameters. Two distinct real-world instances of the problem - being currently operating - were tested with DEPT algorithm. Therefore, with this multiobjective approach for the FAP we are contributing to a really important applicability.
- The Radio Network Design Optimization ProblemPublication . Mendes, Silvio; Gómez-Pulido, Juan A.; Vega-Rodríguez, Miguel A.; Sánchez-Pérez, Juan M.; Sáez, Yago; Isasi, PedroThe fast growth and merging of communication infrastructures and services turned the planning and design of wireless networks into a very complex subject. The Radio Network Design (RND) is a NP-hard optimization problem which consists on the maximization of the coverage of a given area while minimizing the base station (BS) deployment. Solving such problems resourcefully is relevant for many fields of application and has direct impact in engineering, scientific and industrial areas. Its significance is growing due to cost dropping or profit increase allowance and can additionally be applied to several different business targets. Numerous works can be found in the literature dealing with the RND problem, although they all suffer from the same shortfall: a non-comparable efficiency. Therefore, the aim of this work is threefold: first, to offer a reliable RND benchmark reference covering a wide algorithmic spectrum, second, to offer a grand insight of accurately comparisons of efficiency, reliability and swiftness of the different employed algorithmic models and third, to disclose reproducibility details of the implemented models, including simulations of a hardware co-processing accelerator.
- Use of Co-occurrences for Temporal Expressions AnnotationPublication . Craveiro, Olga; Macedo, Joaquim; Madeira, HenriqueThe annotation or extraction of temporal information from text documents is becoming increasingly important in many natural language processing applications such as text summarization, information retrieval, question answering, etc.. This paper presents an original method for easy recognition of temporal expressions in text documents. The method creates semantically classified temporal patterns, using word co-occurrences obtained from training corpora and a pre-defined seed keywords set, derived from the used language temporal references. A participation on a Portuguese named entity evaluation contest showed promising effectiveness and efficiency results. This approach can be adapted to recognize other type of expressions or languages, within other contexts, by defining the suitable word sets and training corpora.
- Video Transcoding TechniquesPublication . Moiron, Sandro; Ghanbari, Mohammed; Assunção, Pedro; Faria, SergioThis chapter addresses the most recent advances in video transcoding and processing architectures for multimedia content adaptation. The first section provides an overview of the state of the art, where video transcoding is described as a key solution to enable seamless interoperability across diverse multimedia communication systems and services. Then, a detailed analysis of relevant transcoding functions is presented, addressing their implementation, coding performance and computational complexity. The different processing architectures that can be used for video transcoding are also described, according to their respective functionalities and application scenarios. Other solutions capable of providing adaptation of coded video to heterogeneous environments, such as scalable video coding and multiple description video coding are also discussed and their main advantages and disadvantages are highlighted. A case study is also presented to illustrate the need and effectiveness of video transcoding in modern applications.