679 research outputs found

    A Rational and Efficient Algorithm for View Revision in Databases

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    The dynamics of belief and knowledge is one of the major components of any autonomous system that should be able to incorporate new pieces of information. In this paper, we argue that to apply rationality result of belief dynamics theory to various practical problems, it should be generalized in two respects: first of all, it should allow a certain part of belief to be declared as immutable; and second, the belief state need not be deductively closed. Such a generalization of belief dynamics, referred to as base dynamics, is presented, along with the concept of a generalized revision algorithm for Horn knowledge bases. We show that Horn knowledge base dynamics has interesting connection with kernel change and abduction. Finally, we also show that both variants are rational in the sense that they satisfy certain rationality postulates stemming from philosophical works on belief dynamics

    A New Rational Algorithm for View Updating in Relational Databases

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    The dynamics of belief and knowledge is one of the major components of any autonomous system that should be able to incorporate new pieces of information. In order to apply the rationality result of belief dynamics theory to various practical problems, it should be generalized in two respects: first it should allow a certain part of belief to be declared as immutable; and second, the belief state need not be deductively closed. Such a generalization of belief dynamics, referred to as base dynamics, is presented in this paper, along with the concept of a generalized revision algorithm for knowledge bases (Horn or Horn logic with stratified negation). We show that knowledge base dynamics has an interesting connection with kernel change via hitting set and abduction. In this paper, we show how techniques from disjunctive logic programming can be used for efficient (deductive) database updates. The key idea is to transform the given database together with the update request into a disjunctive (datalog) logic program and apply disjunctive techniques (such as minimal model reasoning) to solve the original update problem. The approach extends and integrates standard techniques for efficient query answering and integrity checking. The generation of a hitting set is carried out through a hyper tableaux calculus and magic set that is focused on the goal of minimality.Comment: arXiv admin note: substantial text overlap with arXiv:1301.515

    State-of-the-art on evolution and reactivity

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    This report starts by, in Chapter 1, outlining aspects of querying and updating resources on the Web and on the Semantic Web, including the development of query and update languages to be carried out within the Rewerse project. From this outline, it becomes clear that several existing research areas and topics are of interest for this work in Rewerse. In the remainder of this report we further present state of the art surveys in a selection of such areas and topics. More precisely: in Chapter 2 we give an overview of logics for reasoning about state change and updates; Chapter 3 is devoted to briefly describing existing update languages for the Web, and also for updating logic programs; in Chapter 4 event-condition-action rules, both in the context of active database systems and in the context of semistructured data, are surveyed; in Chapter 5 we give an overview of some relevant rule-based agents frameworks

    If it ain’t broke, don’t fix it : An Abductive and Contextual Exploration of Maintenance Deferral

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    Objective: To create academic insights into how organisations approach and manage the maintenance of vendor-supplied information systems software. Approach: Three iterations of the Peircean Abduction methodology lead to the identification, conceptualisation, and application of new knowledge in vendor-supplied Information Systems (IS) maintenance deferral by means of undertaking a qualitative multiple-case study. The research goals are achieved through the appropriation and application of theories from Peircean Abduction and Systemic Functional Linguistics. Research questions: The following abductive statement is created through the application of the Peircean Abduction methodology: The surprising observation, “some organisations, having invested in a vendor-supplied IS software solution, defer the implementation of vendor-supplied maintenance”, is made; However, if “the existence of deterrents to maintenance, requiring a trigger event before the implementation of maintenance” were true, then “maintenance deferral” would be a matter of course. Hence there is a reason to suspect that “the existence of both deterrents, and of triggers” is true. From this abductive statement, three research questions are deduced. The first research question investigates the existence, characteristics and influence of deterrents; the second question investigates the existence, characteristics and influence of triggers. As a consequence of this approach, the final question provides a general understanding of IS maintenance deferral. Methodology: Following the implementation of a systematic literature review methodology, six themes are identified: 1. an acknowledgement that problems exist when considering vendor-supplied software maintenance; 2. deterrents as a driver in behaviour; 3. the occurrence of tipping-points which require vendor-supplied maintenance to be undertaken; 4. the consequences of deferral; 5. the value of maintenance; and 6. the formalisation of a maintenance lifecycle. Taking the insights arising from the systematic literature review, a multiple-case study following the pragmatic framework is constructed from data collected interviewing twelve participants across a diverse set of ten organisations. An abductive approach to this research topic creates opportunities for a comprehensive, well-grounded exploratory contribution to a scarcely investigated research domain. Major findings: The translation of Peircean abduction to an interpretative context generates a rich and substantive contribution to theory and practice. The existence of both deterrents and triggers are strongly supported, leading to the conclusion that maintenance deferral is a matter of course. The development of a new abductive and Systemic Functional Linguistic model enhances the knowledge of maintenance deferral and allows refinement of historical IS maintenance models. Finally, the application of Systems Thinking situates insights from the application of their mode within their respective organisational environments

    State-of-the-art on evolution and reactivity

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    This report starts by, in Chapter 1, outlining aspects of querying and updating resources on the Web and on the Semantic Web, including the development of query and update languages to be carried out within the Rewerse project. From this outline, it becomes clear that several existing research areas and topics are of interest for this work in Rewerse. In the remainder of this report we further present state of the art surveys in a selection of such areas and topics. More precisely: in Chapter 2 we give an overview of logics for reasoning about state change and updates; Chapter 3 is devoted to briefly describing existing update languages for the Web, and also for updating logic programs; in Chapter 4 event-condition-action rules, both in the context of active database systems and in the context of semistructured data, are surveyed; in Chapter 5 we give an overview of some relevant rule-based agents frameworks
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