On Properties of Update Sequences Based on Causal Rejection

We consider an approach to update nonmonotonic knowledge bases represented as extended logic programs under answer set semantics. New information is incorporated into the current knowledge base subject to a causal rejection principle enforcing that, in case of conflicts, more recent rules are preferred and older rules are overridden. Such a rejection principle is also exploited in other approaches to update logic programs, e.g., in dynamic logic programming by Alferes et al. We give a thorough analysis of properties of our approach, to get a better understanding of the causal rejection principle. We review postulates for update and revision operators from the area of theory change and nonmonotonic reasoning, and some new properties are considered as well. We then consider refinements of our semantics which incorporate a notion of minimality of change. As well, we investigate the relationship to other approaches, showing that our approach is semantically equivalent to inheritance programs by Buccafurri et al. and that it coincides with certain classes of dynamic logic programs, for which we provide characterizations in terms of graph conditions. Therefore, most of our results about properties of causal rejection principle apply to these approaches as well. Finally, we deal with computational complexity of our approach, and outline how the update semantics and its refinements can be implemented on top of existing logic programming engines.Comment: 59 pages, 2 figures, 3 tables, to be published in "Theory and Practice of Logic Programming

Vienna Circle and Logical Analysis of Relativity Theory

In this paper we present some of our school's results in the area of building up relativity theory (RT) as a hierarchy of theories in the sense of logic. We use plain first-order logic (FOL) as in the foundation of mathematics (FOM) and we build on experience gained in FOM. The main aims of our school are the following: We want to base the theory on simple, unambiguous axioms with clear meanings. It should be absolutely understandable for any reader what the axioms say and the reader can decide about each axiom whether he likes it. The theory should be built up from these axioms in a straightforward, logical manner. We want to provide an analysis of the logical structure of the theory. We investigate which axioms are needed for which predictions of RT. We want to make RT more transparent logically, easier to understand, easier to change, modular, and easier to teach. We want to obtain deeper understanding of RT. Our work can be considered as a case-study showing that the Vienna Circle's (VC) approach to doing science is workable and fruitful when performed with using the insights and tools of mathematical logic acquired since its formation years at the very time of the VC activity. We think that logical positivism was based on the insight and anticipation of what mathematical logic is capable when elaborated to some depth. Logical positivism, in great part represented by VC, influenced and took part in the birth of modern mathematical logic. The members of VC were brave forerunners and pioneers.Comment: 25 pages, 1 firgure

A New Rational Algorithm for View Updating in Relational Databases

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

A bivariant Yoneda lemma and (∞,2)(\infty,2)-categories of correspondences

Everyone knows that if you have a bivariant homology theory satisfying a base change formula, you get an representation of a category of correspondences. For theories in which the covariant and contravariant transfer maps are in mutual adjunction, these data are actually equivalent. In other words, a 2-category of correspondences is the universal way to attach to a given 1-category a set of right adjoints that satisfy a base change formula . Through a bivariant version of the Yoneda paradigm, I give a definition of correspondences in higher category theory and prove an extension theorem for bivariant functors. Moreover, conditioned on the existence of a 2-dimensional Grothendieck construction, I provide a proof of the aforementioned universal property. The methods, morally speaking, employ the `internal logic' of higher category theory: they make no explicit use of any particular model.Comment: 60 page

When Institutional Logics Meet Information and Communication Technologies: Examining Hybrid Information Practices in Ghana’s Agriculture

In this paper, we describe how changes in the availability of information artifacts—in particular, information and communication technologies (ICTs)—among smallholder farmers in Ghana, led to a process of hybridization of information practices, and how this process could be linked to underlying institutional change. We use the notions of institutional carriers and activity systems to study the evolution of the prevailing “smallholder” institutional logic of Ghanaian agriculture toward an incoming “value-chain” institutional logic concerned with linking farmers to output markets, improving the knowledge base in agriculture, and increasing its information intensity. We draw on a mixed-methods approach, including in-depth qualitative interviews, focus groups, observations, and detailed secondary quantitative data. We cultivate activity theory as a practice-based lens for structuring inquiry into institutional change. We find that information artifacts served to link the activities of farmers that were embedded in the smallholder logic with those of agricultural-development actors that promoted the value-chain logic. Hybridization occurred through the use of artifacts with different interaction modalities. In terms of conceptualizing change, our findings suggest that hybridization of the two logics may be an intermediary point in the long transition from the smallholder toward the value-chain logic

Power constructs and propositional systems

Bibliography : p. 161-176.Propositional systems are deductively closed sets of sentences phrased in the language of some propositional logic. The set of systems of a given logic is turned into an algebra by endowing it with a number of operations, and into a relational structure by endowing it with a number of relations. Certain operations and relations on systems arise from some corresponding base operation or relation, either on sentences in the logic or on propositional valuations. These operations and relations on systems are called power constructs. The aim of this thesis is to investigate the use of power constructs in propositional systems. Some operations and relations on systems that arise as power constructs include the Tarskian addition and product operations, the contraction and revision operations of theory change, certain multiple- conclusion consequence relations, and certain relations of verisimilitude and simulation. The logical framework for this investigation is provided by the definition and comparison of a number of multiple-conclusion logics, including a paraconsistent three-valued logic of partial knowledge

Using a realist approach to evaluate smoking cessation interventions targeting pregnant women and young people

Background This paper describes a study protocol designed to evaluate a programme of smoking cessation interventions targeting pregnant women and young people living in urban and rural locations in Northeast Scotland. The study design was developed on so-called 'realist' evaluation principles, which are concerned with the implementation of interventions as well as their outcomes. Methods/design A two-phased study was designed based on the Theory of Change (TOC) using mixed methods to assess both process and outcome factors. The study was designed with input from the relevant stakeholders. The mixed-methods approach consists of semi-structured interviews with planners, service providers, service users and non-users. These qualitative interviews will be analysed using a thematic framework approach. The quantitative element of the study will include the analysis of routinely collected data and specific project monitoring data, such as data on service engagement, service use, quit rates and changes in smoking status. Discussion The process of involving key stakeholders was conducted using logic modelling and TOC tools. Engaging stakeholders, including those responsible for funding, developing and delivering, and those intended to benefit from interventions aimed at them, in their evaluation design, are considered by many to increase the validity and rigour of the subsequent evidence generated. This study is intended to determine not only the components and processes, but also the possible effectiveness of this set of health interventions, and contribute to the evidence base about smoking cessation interventions aimed at priority groups in Scotland. It is also anticipated that this study will contribute to the ongoing debate about the role and challenges of 'realist' evaluation approaches in general, and the utility of logic modelling and TOC approaches in particular, for evaluation of complex health interventions

Taxes, Saving, and Macroeconomics

In response to increasing calls for policies to raise the U.S. saving rate, proposals are once again being offered in Congress to change the tax base from income to consumption. Beyond the important issues of income distribution (that is, outright unfairness) inherent in such a plan, it would simply not work. Indeed, it is based on a fundamental mismeasurement of what counts as saving in the U.S. economy. The logical sequence underlying this proposal is wrong at two crucial points: lowering or eliminating taxes on saving is unlikely to increase saving, and higher saving would be unlikely to increase investment in any case (and would, more likely, decrease investment). The usual crowding-out logic is based on limited evidence and inadequate theory. Finally, the interaction between monetary and fiscal policy is currently perverse. Contractionary fiscal policy (which is what is implied by these proposals) will not be counter-balanced by timely and adequate monetary stimulus. The Federal Reserve is likely to wait too long to respond, either due to excessive caution about the effectiveness of the fiscal policy change or to take advantage of an opportunity to lower inflation still further before allowing the economy to recover

The Ikea message: deconstructing Ikea's environmental discourse - Sustainability and profit

During the recent decades, concerns about the environment and climate change have progressively gained importance in political, social and economic arenas. Amid environmental conferences and international political negotiations, on the business side corporations have scrambled to find ways to secure themselves and even prosper on an environmentally aware consumer base. This thesis examines how Ikea conceptualizes environmental problems and solutions. It will be argued that the company draws heavily on the theory of ecological modernization in its environmental policymaking. In short, ecological modernization is a set of principles that presupposes that resolving the environmental crisis can be done within the current capitalistic system. The aim of this thesis is to investigate the logic of the discourse of ecological modernization and Ikea's environmental policies in particular. Indications that this logic is fundamentally based on continuing consumption and economic growth will be presented. By taking the standpoint that overconsumption is a cause of environmental degradation, a central question is how Ikea draws attention away from this issue. To this end, the theoretical approach of human ecology is employed and a critical discourse analysis is conducted on three Ikea documents that details the company's environmental policies and strategies. The results show that Ikea refrain from formulating consumption as an issue of concern, and instead focuses on conceptualizing environmental solutions in innovation, technology, and unclear definitions of sustainability. Additionally, the results reveal that Ikea seeks to increase consumption (defined as sustainable) as part of its environmental policies