3 research outputs found

    Evolving Graphs by Graph Programming

    Get PDF
    Graphs are a ubiquitous data structure in computer science and can be used to represent solutions to difficult problems in many distinct domains. This motivates the use of Evolutionary Algorithms to search over graphs and efficiently find approximate solutions. However, existing techniques often represent and manipulate graphs in an ad-hoc manner. In contrast, rule-based graph programming offers a formal mechanism for describing relations over graphs. This thesis proposes the use of rule-based graph programming for representing and implementing genetic operators over graphs. We present the Evolutionary Algorithm Evolving Graphs by Graph Programming and a number of its extensions which are capable of learning stateful and stateless digital circuits, symbolic expressions and Artificial Neural Networks. We demonstrate that rule-based graph programming may be used to implement new and effective constraint-respecting mutation operators and show that these operators may strictly generalise others found in the literature. Through our proposal of Semantic Neutral Drift, we accelerate the search process by building plateaus into the fitness landscape using domain knowledge of equivalence. We also present Horizontal Gene Transfer, a mechanism whereby graphs may be passively recombined without disrupting their fitness. Through rigorous evaluation and analysis of over 20,000 independent executions of Evolutionary Algorithms, we establish numerous benefits of our approach. We find that on many problems, Evolving Graphs by Graph Programming and its variants may significantly outperform other approaches from the literature. Additionally, our empirical results provide further evidence that neutral drift aids the efficiency of evolutionary search

    Specialising Parsers for Queries

    Get PDF
    Many software systems consist of data processing components that analyse large datasets to gather information and learn from these. Often, only part of the data is relevant for analysis. Data processing systems contain an initial preprocessing step that filters out the unwanted information. While efficient data analysis techniques and methodologies are accessible to non-expert programmers, data preprocessing seems to be forgotten, or worse, ignored. This despite real performance gains being possible by efficiently preprocessing data. Implementations of the data preprocessing step traditionally have to trade modularity for performance: to achieve the former, one separates the parsing of raw data and filtering it, and leads to slow programs because of the creation of intermediate objects during execution. The efficient version is a low-level implementation that interleaves parsing and querying. In this dissertation we demonstrate a principled and practical technique to convert the modular, maintainable program into its interleaved efficient counterpart. Key to achieving this objective is the removal, or deforestation, of intermediate objects in a program execution. We first show that by encoding data types using Böhm-Berarducci encodings (often referred to as Church encodings), and combining these with partial evaluation for function composition we achieve deforestation. This allows us to implement optimisations themselves as libraries, with minimal dependence on an underlying optimising compiler. Next we illustrate the applicability of this approach to parsing and preprocessing queries. The approach is general enough to cover top-down and bottom-up parsing techniques, and deforestation of pipelines of operations on lists and streams. We finally present a set of transformation rules that for a parser on a nested data format and a query on the structure, produces a parser specialised for the query. As a result we preserve the modularity of writing parsers and queries separately while also minimising resource usage. These transformation rules combine deforested implementations of both libraries to yield an efficient, interleaved result

    Specification and refinement of software connectors

    Get PDF
    Tese de doutoramento em Informática (área de conhecimento de Fundamentos da Computação)Modern computer based systems are essentially based on the cooperation of distributed, heterogeneous component organized into open software architectures that, moreover, can survive in loosely-coupled environments and be easily adapted to changing application requirements. Such is the case, for example, of applications designed to take advantage of the increased computational power provided by massively parallel systems or of the whole business of Internet-based software development. In order to develop such systems in a systematic way, the focus in development method has switched, along the last decade, from functional to structural issues: both data and processes are encapsulated into software units which are connected into large systems resorting, to a number of techniques intended to support reusability and modifiability. Actually, the complexity and ubiquity achieved by software in present times makes it imperative, more than ever, the availability of both technologies and sound methods to drive its development. Programming ‘in–the–large’, component–based programming and software architecture become popular expressions which embody this sort of concerns and correspond to driving forces in current software engineering. In such a context this thesis aims at introducing formal models for software connectors as well as the corresponding notions of equivalence and refinement upon which calculation principles for reasoning and transforming connector-based software architectures can be developed. This research adopts an exogenous coordination point of view in order to deal with components’ temporal and spatial decoupling and, therefore, to provide support for looser levels of inter-component dependency. The thesis also characterises a notion of behavioural interface for components and services. Interfaces and connectors are put together to form configurations, an abstraction for representing software architectures. A prototype implementation of a subset of the proposed models is provided, in the form of a HASKELL library, as a proof of concept. Furthermore, the thesis reports on a case study in which exogenous coordination is applied to the specification of interactive systems.Um número crescente de sistemas computacionais é baseado na cooperação de componentes interdependentes e heterogêneas, organizadas em arquiteturas abertas capazes de sobreviverem em ambientes altamente distribuídos e facilmente adaptáveis a alterações nos requisitos das aplicações que os suportam. Tal é o caso, por exemplo, de aplicações que exploram o poder computacional de sistemas massivamente paralelos ou de sistemas desenvolvidos sobre a Internet. Para desenvolver este tipo de sistemas de forma sistemática, o foco nos métodos de desenvolvimento alterou-se, ao longo da última década, dos aspectos funcionais para os aspectos estruturais dos sistemas: ambos, estruturas de dados e processos são encapsulados em unidades computacionais que são conectadas em grandes sistemas utilizando-se de diversas técnicas que se pretendem capazes de suportar a reutilização e a adaptabilidade do software. Na realidade, a complexidade e ubiqüidade atingidas pelo software nos dias correntes tornam imperativo, mais do que nunca, a disponibilidade de tecnologias e sólidos métodos para conduzir este processo de desenvolvimento. Programação ’em-grande-escala’, programação baseada em componentes e arquiteturas de software são expressões populares que englobam esta preocupação e correspondem aos esforços direcionados pela engenharia de software. Em tal contexto, esta tese tem por objetivo introduzir modelos formais para conectores de software bem como as correspondentes noções de equivalência e refinamento que suportem cálculos para raciocinar e transformar arquiteturas de software baseada em conectores. Esta pesquisa adota um ponto de vista de coordenação exógena para lidar com a separação espacial e temporal das componentes e suportar níveis elevados de independência entre componentes. A tese caracteriza, ainda, uma noção de interface comportamental para componentes e serviços. Interfaces e conectores agregam-se para formar configurações, uma abstração introduzida para representar arquiteturas de software. A implementação, em protótipo, de parte dos modelos propostos, sob a forma de uma biblioteca em HASKELL, é fornecida como prova de conceito. Finalmente, a tese percorre um estudo de caso em que coordenação exôgena é utilizada na especificação de sistemas interactivos.Fundação para a Ciência e a Tecnologia (FCT), SFRH/BD/11083/200
    corecore