Metaphorisms in programming

This paper introduces the metaphorism pattern of relational specification and addresses how specification following this pattern can be refined into recursive programs. Metaphorisms express input-output relationships which preserve relevant information while at the same time some intended optimization takes place. Text processing, sorting, representation changers, etc., are examples of metaphorisms. The kind of metaphorism refinement proposed in this paper is a strategy known as change of virtual data structure. It gives sufficient conditions for such implementations to be calculated using relation algebra and illustrates the strategy with the derivation of quicksort as example.The author wishes to thank the anonymous referees for their comments and suggestions. This work is funded by ERDF - European Regional Development Fund through the COMPETE Programme (operational programme for competitiveness) and by National Funds through the FCT - Funda¸c˜ao para a Ciˆencia e a Tecnologia (Portuguese Foundation for Science and Technology) within project FCOMP-01-0124-FEDER-02053

Greedy and dynamic programming by calculation

Dissertação mestrado integrado em Informatics EngineeringThe mathematical study of the greedy algorithm provides a blueprint for the study of Dynamic Programming (DP), whose body of knowledge is largely unorganized, remaining obscure to a large part of the software engineering community. This study aims to structure this body of knowledge, narrowing the gap between a purely examplebased approach to DP and its scientific foundations. To that effect, matroid theory is leveraged through a pointfree relation algebra, which is applied to greedy and DP problems. A catalogue of such problems is compiled, and a broad characterization of DP algorithms is given. Alongside, the theory underlying the thinning relational operator is explored.O estudo matemático do algoritmo ganancioso («greedy») serve como guia para o estudo da programação dinâmica, cujo corpo de conhecimento permanece desorganizado e obscuro a uma grande parte da comunidade de engenharia de software. Este estudo visa estruturar esse corpo de conhecimento, fazendo a ponte entre a abordagem popular baseada em exemplos e os métodos mais teóricos da literatura científica. Para esse efeito, a teoria dos matroides é explorada pelo uso de uma álgebra de relações pointfree, e aplicada a problemas «greedy» e de programação dinâmica. Um catálogo de tais problemas é compilado, e é feita uma caraterização geral de algoritmos de programação dinâmica. Em paralelo, é explorada a teoria do combinador relacional de «thinning».This work is financed by National Funds through the Portuguese funding agency, FCT - Fundação para a Ciência e a Tecnologia, within project UIDB/50014/202

The Index and Core of a Relation. With Applications to the Axiomatics of Relation Algebra

We introduce the general notions of an index and a core of a relation. We postulate a limited form of the axiom of choice -- specifically that all partial equivalence relations have an index -- and explore the consequences of adding the axiom to standard axiom systems for point-free reasoning. Examples of the theorems we prove are that a core/index of a difunction is a bijection, and that the so-called ``all or nothing'' axiom used to facilitate pointwise reasoning is derivable from our axiom of choice

On difunctions

The notion of a difunction was introduced by Jacques Riguet in 1948. Since then it has played a prominent role in database theory, type theory, program specification and process theory. The theory of difunctions is, however, less known in computing than it perhaps should be. The main purpose of the current paper is to give an account of difunction theory in relation algebra, with the aim of making the topic more mainstream. As is common with many important concepts, there are several different but equivalent characterisations of difunctionality, each with its own strength and practical significance. This paper compares different proofs of the equivalence of the characterisations. A well-known property is that a difunction is a set of completely disjoint rectangles. This property suggests the introduction of the (general) notion of the “core” of a relation; we use this notion to give a novel and, we believe, illuminating characterisation of difunctionality as a bijection between the classes of certain partial equivalence relations

Components and acyclicity of graphs. An exercise in combining precision with concision

Central to algorithmic graph theory are the concepts of acyclicity and strongly connected components of a graph, and the related search algorithms. This article is about combining mathematical precision and concision in the presentation of these concepts. Concise formulations are given for, for example, the reflexive-transitive reduction of an acyclic graph, reachability properties of acyclic graphs and their relation to the fundamental concept of “definiteness”, and the decomposition of paths in a graph via the identification of its strongly connected components and a pathwise homomorphic acyclic subgraph. The relevant properties are established by precise algebraic calculation. The combination of concision and precision is achieved by the use of point-free relation algebra capturing the algebraic properties of paths in graphs, as opposed to the use of pointwise reasoning about paths between nodes in graphs

Wireless spectres : space and the re-enchantment of invisible technologies

PhD ThesisThis thesis examines wireless technologies, and the way they are integrated in architecture to produce new spatial experiences. The thesis draws from the school of New Materialism in suggesting that the materiality of wireless infrastructure is not a fixed property that can be captured and revealed, but that is rather contingent on transactions with other materials and through human interaction. Measuring and representing wireless involves a series of transactions — the construction of a probe to measure signal strength, logical processes involved in the transformation of values into visible patterns, and a choreography of movement as the probe is deployed in space. Following notions of agential realism and digital materiality, I propose that these transactions construct the materiality of wireless, and aim to position the process of representation as a form of speculative design which deals with the emergent materialities of wireless. In this context, representations do not increase literacy, but rather enable us to think of wireless infrastructure in ways which go beyond the convenient transfer of information to think of them as ways of creating new spatial experiences. The thesis develops a creative practice approach that adapts tools and techniques developed in explorations by others to engage with the material transactions in representing wireless. I introduce the strategy of material conceit to draw on historical precedents that saw wireless technologies as spectres. The exploration results in a body of work comprising instruments, photographs and installations which constitute allusive images aimed at contributing renewed notions of how wireless can be integrated in the design of artefacts and space

Políticas de Copyright de Publicações Científicas em Repositórios Institucionais: O Caso do INESC TEC

A progressiva transformação das práticas científicas, impulsionada pelo desenvolvimento das novas Tecnologias de Informação e Comunicação (TIC), têm possibilitado aumentar o acesso à informação, caminhando gradualmente para uma abertura do ciclo de pesquisa. Isto permitirá resolver a longo prazo uma adversidade que se tem colocado aos investigadores, que passa pela existência de barreiras que limitam as condições de acesso, sejam estas geográficas ou financeiras. Apesar da produção científica ser dominada, maioritariamente, por grandes editoras comerciais, estando sujeita às regras por estas impostas, o Movimento do Acesso Aberto cuja primeira declaração pública, a Declaração de Budapeste (BOAI), é de 2002, vem propor alterações significativas que beneficiam os autores e os leitores. Este Movimento vem a ganhar importância em Portugal desde 2003, com a constituição do primeiro repositório institucional a nível nacional. Os repositórios institucionais surgiram como uma ferramenta de divulgação da produção científica de uma instituição, com o intuito de permitir abrir aos resultados da investigação, quer antes da publicação e do próprio processo de arbitragem (preprint), quer depois (postprint), e, consequentemente, aumentar a visibilidade do trabalho desenvolvido por um investigador e a respetiva instituição. O estudo apresentado, que passou por uma análise das políticas de copyright das publicações científicas mais relevantes do INESC TEC, permitiu não só perceber que as editoras adotam cada vez mais políticas que possibilitam o auto-arquivo das publicações em repositórios institucionais, como também que existe todo um trabalho de sensibilização a percorrer, não só para os investigadores, como para a instituição e toda a sociedade. A produção de um conjunto de recomendações, que passam pela implementação de uma política institucional que incentive o auto-arquivo das publicações desenvolvidas no âmbito institucional no repositório, serve como mote para uma maior valorização da produção científica do INESC TEC.The progressive transformation of scientific practices, driven by the development of new Information and Communication Technologies (ICT), which made it possible to increase access to information, gradually moving towards an opening of the research cycle. This opening makes it possible to resolve, in the long term, the adversity that has been placed on researchers, which involves the existence of barriers that limit access conditions, whether geographical or financial. Although large commercial publishers predominantly dominate scientific production and subject it to the rules imposed by them, the Open Access movement whose first public declaration, the Budapest Declaration (BOAI), was in 2002, proposes significant changes that benefit the authors and the readers. This Movement has gained importance in Portugal since 2003, with the constitution of the first institutional repository at the national level. Institutional repositories have emerged as a tool for disseminating the scientific production of an institution to open the results of the research, both before publication and the preprint process and postprint, increase the visibility of work done by an investigator and his or her institution. The present study, which underwent an analysis of the copyright policies of INESC TEC most relevant scientific publications, allowed not only to realize that publishers are increasingly adopting policies that make it possible to self-archive publications in institutional repositories, all the work of raising awareness, not only for researchers but also for the institution and the whole society. The production of a set of recommendations, which go through the implementation of an institutional policy that encourages the self-archiving of the publications developed in the institutional scope in the repository, serves as a motto for a greater appreciation of the scientific production of INESC TEC