1,721,037 research outputs found
HYPOTHETICAL REASONING ABOUT ACTIONS: FROM SITUATION CALCULUS TO EVENT CALCULUS
No full textHypothetical reasoning about actions is the activity of preevaluating the effect of performing actions in a changing domain; this reasoning underlies applications of knowledge representation, such as planning and explanation generation. Action effects are often specified in the language of situation calculus, introduced by McCarthy and Hayes in 1969. More recently, the event calculus has been defined to describe actual actions, i.e., those that have occurred in the past, and their effects on the domain. Altough the two formalisms share the basic ontology of atomic actions and fluents, situation calculus cannot represent actual actions while event calculus cannot represent hypotethical actions. In this article, the language and the axioms of event calculus are extended to allow representing and reasoning about hypothetical actions, performed either at the present time or in the past, altough counterfactuals are not supported. Both event calculus and its extension are defined as logic programs so that theories are readily adaptable for Prolog query interpretation. For a reasonably large class of theories and queries, Prolog interpretation is shown to be sound and complete w.r.t. the main semantics for logic programs
Flexible interpolated-binary search over sorted sets
Full text linkWe revisit the classical algorithms for searching over sorted sets and introduce
a new algorithm, called adaptive search, that combines the good features of Interpolation search and those of Binary search.
W.r.t. Insertion sort, only a constant number of extra comparisons is introduced.
Yet, under several relevant input data distributions our algorithm shows average case cost comparable to that of Interpolation Search, i.e., O(log log n) while the worst case cost is always in O(log n), as with Binary search.
This result compares well with the traditional result of Santoro and Sidney Interpolation-Binary Search and the recent approach of Demaine et al. on searching non-independent data
Experimental Analysis of Graph-based Answer Set Computation over Parallel and Distributed Architectures
No full textThis article presents a distributed version of the ADJSOLVER algorithm for computing the answer sets of logic programs. ADJSOLVER operates a classical branch-and-bound structure; its intrinsic parallelism is exploited to control, with a centralized architecture, the delegation of promising search subspaces to distributed handling agents. ADJSOLVER has been implemented and tested on a Beowulf platform, using MPI message passing. The communication overhead was minimized by adopting a compact representation of the data exchanged among agents and by reusing previously-computed partial solutions
Characterizing and computing stable models of logic programs: The non-stratified case
No full textStable Logic Programming (SLP) is an emergent, alternative style of logic programming: each solution to a problem is represented by a stable model of a deductive database/function-free logic program encoding the problem itself. Several implementations now exist for stable logic programming, and their performance is rapidly improving. To make SLP generally applicable, it should be possible to check for consistency (i.e., existence of stable models) of the input program before attempting to answer queries. In the literature, only rather strong sufficient conditions have been proposed for consistency, e.g., stratification. This paper extends these results in several directions. First, the syntactic features of programs, viz. cyclic negative dependencies, affecting the existence of stable models are characterized, and their relevance is discussed. Next, a new graph representation of logic programs, the Extended Dependency Graph (EDG), is introduced, which conveys enough information for reasoning about stable models (while the traditional Dependency Graph does not). Finally, we show that the problem of the existence of stable models can be reformulated in terms of coloring of the EDG
Trust Models go to the Web: Learning how to Trust Strangers
Full text linkWe study emerging traits of interpersonal and social trust in online social networks of needs (OSNNs), where
trust interactions start online and evolve into in-person meetings. We present a lightweight web scraping
solution to harness data from online social networks; thanks to it we were able to monitor a nation-wide
portal for childcare and see the evolution of online reviews from both families and carers. We analysed the
data by first considering topological information to test centrality metrics as proxies for trustworthiness. Next,
we focused on features/profile analysis and tested the Castelfranchi–Falcone trust model from psychology
(CF-T), fitting it to online reviews of childcare services. Even though such reviews are relatively scarce and
seemingly skewed, we feature-engineered the CF-T model to predict the evolution of reviews, treated as
proxies for trust. By aggregating CF-T scores at the regional level, we discovered a strong correlation with
per capita GDP, which suggests that high levels of trust in social networks of needs reflect social capital
Reasoning about lava effusion : from Geographical Information Systems to Answer Set Programming
Full text linkGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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