27 research outputs found

    Every normal logic program has a 2-valued semantics: theory, extensions, applications, implementations

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    Trabalho apresentado no âmbito do Doutoramento em Informática, como requisito parcial para obtenção do grau de Doutor em InformáticaAfter a very brief introduction to the general subject of Knowledge Representation and Reasoning with Logic Programs we analyse the syntactic structure of a logic program and how it can influence the semantics. We outline the important properties of a 2-valued semantics for Normal Logic Programs, proceed to define the new Minimal Hypotheses semantics with those properties and explore how it can be used to benefit some knowledge representation and reasoning mechanisms. The main original contributions of this work, whose connections will be detailed in the sequel, are: • The Layering for generic graphs which we then apply to NLPs yielding the Rule Layering and Atom Layering — a generalization of the stratification notion; • The Full shifting transformation of Disjunctive Logic Programs into (highly nonstratified)NLPs; • The Layer Support — a generalization of the classical notion of support; • The Brave Relevance and Brave Cautious Monotony properties of a 2-valued semantics; • The notions of Relevant Partial Knowledge Answer to a Query and Locally Consistent Relevant Partial Knowledge Answer to a Query; • The Layer-Decomposable Semantics family — the family of semantics that reflect the above mentioned Layerings; • The Approved Models argumentation approach to semantics; • The Minimal Hypotheses 2-valued semantics for NLP — a member of the Layer-Decomposable Semantics family rooted on a minimization of positive hypotheses assumption approach; • The definition and implementation of the Answer Completion mechanism in XSB Prolog — an essential component to ensure XSB’s WAM full compliance with the Well-Founded Semantics; • The definition of the Inspection Points mechanism for Abductive Logic Programs;• An implementation of the Inspection Points workings within the Abdual system [21] We recommend reading the chapters in this thesis in the sequence they appear. However, if the reader is not interested in all the subjects, or is more keen on some topics rather than others, we provide alternative reading paths as shown below. 1-2-3-4-5-6-7-8-9-12 Definition of the Layer-Decomposable Semantics family and the Minimal Hypotheses semantics (1 and 2 are optional) 3-6-7-8-10-11-12 All main contributions – assumes the reader is familiarized with logic programming topics 3-4-5-10-11-12 Focus on abductive reasoning and applications.FCT-MCTES (Fundação para a Ciência e Tecnologia do Ministério da Ciência,Tecnologia e Ensino Superior)- (no. SFRH/BD/28761/2006

    Interactive Code Generation

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    This thesis presents two approaches to code generation (synthesis) along with a discussion of other related and influential works, their ideas and relations to these approaches. The common goal of these approaches is to efficiently and effectively assist developers in software development by synthesizing code for them and save their efforts. The two presented approaches differ in the nature of the synthesis problem they try to solve. They are targeted to be useful in different scenarios, apply different set of techniques and can even be complementary. The first approach to code synthesis relies on typing information of a program to define and drive the synthesis process. The main requirement imposes that synthesized solutions have the desired type. This can aid developers in many scenarios of modern software development which typically involves composing functionality from existing libraries which expose a rich API. Our observation is that the developer usually does not know the right combination for composing API calls but knows the type of the desired expression. With the basis being the well-known type inhabitation problem we introduce a succinct representation for type judgements that significantly speed up the search for type inhabitants. Our method finds multiple solutions and ranks them before offering them to the developer. We implemented this approach as a plugin for the Eclipse IDE for Scala. From the evaluation we concluded that this approach goes beyond available related techniques and can be very useful in practical software development. In the second approach, synthesis of code is driven by explicit specification of code in terms of (formal) specification. The goal is to allow the developer to specify a program, by giving formal description of its behavior, rather than writing the code - the actual implementation is synthesized automatically. The practical value of such synthesis is immediately clear since this problem is generally hard. The approach solves this problem by combining existing tools for code generation, verification and testing within the synthesis process, and applies techniques for speeding it up. Interesting modifications to the synthesis driven by types were made to allow synthesizing expressions lazily, on demand, by searching for solutions in an incremental fashion. Results of the evaluation on several examples show that the implementation can be effective and useful in practice, while the approach still offers a lot of room for improvements

    Time for change: a study of enrolment decision dynamics for admission into English secondary education

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    Cross-sectional studies suggest a prevalence of mental health problems from the age that children change to English secondary schools but there are few longitudinal appraisals of these issues and how enrolment policies influence psychological wellbeing. This research focuses on key factors linking competition for secondary schools and family responses to such challenges to determine enrolment policies that can sustain wellbeing longer-term. Integrated, model-based multimethodology was used in this urban, case-based study. Views were induced from multi-agency, expert practitioners to agree a system dynamics concept model. Parental decision-making behaviours were deduced by survey to understand key factors for model calibration. Dynamic system sensitivities were abduced from the simulation model before comparing long-term psychosocial impacts on children from expert, policy-support suggestions. Modelling demonstrates that two principal feedback loops influence family psychosocial systems when deciding secondary schools (parent-child wellbeing reinforcement plus knowledge of schools balancing parent concerns). Exogenous competition stressors on psychosocial systems can erode parent knowledge while testing student resolve. Competition guidance to remove risk-laden school options (league table comparison) before sequencing any remaining choices by profit (school visits), are not always used deciding urban secondary schools. Instead, families lacking experience can adopt decisive styles based on parent needs alone. Given autocratic leadership, child wellbeing rapidly deteriorates when student needs cannot be met by schools. Rather than ending student-selective entrance tests or raising knowledge of schools at visits, effective multi-agency support policy helps by increasing school choice debate frequency within families to address psychosocial system imbalances. The research makes a clear, three-way contribution to knowledge. Firstly, intrinsic case study theory is enhanced by data triangulation between induced, deduced and abduced research approaches. Secondly, the system dynamics discipline is strengthened by studying compulsory school enrolment. Finally, developing practice-based policy through multi-agency groups endorses cooperative rather than unilateral solutions, for helping change lives

    Assessing the feasibility of using system dynamics in the evaluation of shared service centres

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    A thesis submitted to the University of Bedfordshire, in partial fulfilment of the requirements for the degree of doctor of Philosophy.In order to make businesses more effective and efficient, various approaches have been proposed to improve business structures and processes so as to better support corporate objectives. From the 1990’s onwards, enabled by advances in computer technology, one popular approach has been to develop a Shared Service Centre (SSC), whereby various (mostly back office) activities previously organised and attached to separate business units (often) on a national / regional basis, have been consolidated into a single SSC. In common with other business process improvement / re-engineering projects, the success of these transformations have been varied with both successes and failures reported. From the available literature, it was determined that the SSC transformation process especially with regards to the use of a decision support system such as System Dynamics (SD), that will allow for experimentation by SSC implementers has not been rigorously researched or published and thus this is the gap in knowledge that this research seeks to address. This research uses a multiple paradigm / mixed method (exploratory sequential) research approach (Case Study and System Dynamics). This research contends that, given the patchy outcomes, significant cost implications and the adverse impact on organisations when the SSC Transition / Transformation process fails, the current SSC Transition approaches (methodology) have not been effective. Given that the objective of the SSC Transition approach is to ensure a smooth implementation of the proposed Shared Service Centre, this research argues that a simulation approach, grounded in systems thinking, is a credible way of examining the transformation process and evaluating both the transition methodology and the potential outcomes from that process. This research therefore proposes the use of a decision support system (System Dynamics / Simulation) perspective as a credible way of evaluating Shared Service Centres prior to designing and building them and to enhance the project management methodology for SSCs. Furthermore, the research depicts the cause / effect relationship among the SSC Critical Success Factors. Policy intervention tools can then be generated to mitigate against any adverse findings. The research findings showed that, the proposed Shared Service Centre is impacted by three main factors, the selection of a service delivery model, SSC Critical Success Factors and the SSC Phases; and that there is a cause / effect relationship among the SSC Critical Success Factors. In addition, the motives and critical success factors for organisational change were also found to be applicable to SSCs; and that during the SSC Transition phase, SSC Critical Success Factors, Staff Management and the Management of Transactional Activities were found to be important for a successful transition. A further contribution to knowledge is that the use of SD enables the testing of the SSC phenomenon in a new setting. For future research, the constructed SD model can be used as a basis for future organisational SSC Transitions and policy development

    Human decision-making in computer security incident response

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    Background: Cybersecurity has risen to international importance. Almost every organization will fall victim to a successful cyberattack. Yet, guidance for computer security incident response analysts is inadequate. Research Questions: What heuristics should an incident analyst use to construct general knowledge and analyse attacks? Can we construct formal tools to enable automated decision support for the analyst with such heuristics and knowledge? Method: We take an interdisciplinary approach. To answer the first question, we use the research tradition of philosophy of science, specifically the study of mechanisms. To answer the question on formal tools, we use the research tradition of program verification and logic, specifically Separation Logic. Results: We identify several heuristics from biological sciences that cybersecurity researchers have re-invented to varying degrees. We consolidate the new mechanisms literature to yield heuristics related to the fact that knowledge is of clusters of multi-field mechanism schema on four dimensions. General knowledge structures such as the intrusion kill chain provide context and provide hypotheses for filling in details. The philosophical analysis answers this research question, and also provides constraints on building the logic. Finally, we succeed in defining an incident analysis logic resembling Separation Logic and translating the kill chain into it as a proof of concept. Conclusion: These results benefits incident analysis, enabling it to expand from a tradecraft or art to also integrate science. Future research might realize our logic into automated decision-support. Additionally, we have opened the field of cybersecuity to collaboration with philosophers of science and logicians
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