1,720,958 research outputs found
Equivalences and Congruences on Infinite Conway Games
Full text linkTaking the view that infinite plays are draws, we study Conway non-terminating games and non-losing strategies. These admit a sharp coalgebraic presentation, where non-terminating games are seen as a final coalgebra and game contructors, such as disjunctive sum, as final morphisms. We have shown, in a previous paper, that Conway's theory of terminating games can be rephrased naturally in terms of game (pre)congruences. Namely, various conceptually independent notions of equivalence can be defined and shown to coincide on Conway's terminating games. These are the equivalence induced by the ordering on surreal numbers, the contextual equivalence determined by observing what player has a winning strategy, Joyal's categorical equivalence, and, for impartial games, the denotational equivalence induced by Grundy semantics. In this paper, we discuss generalizations of such equivalences to non-terminating games and non-losing strategies. The scenario is even more rich and intriguing in this case. In particular, we investigate efficient characterizations of the contextual equivalence, and we introduce a category of fair strategies and a category of fair pairs of strategies, both generalizing Joyal's category of Conway games and winning strategies. Interestingly, the category of fair pairs captures the equivalence defined by Berlekamp, Conway, Guy on loopy games
Coalgebraic Semantics and Observational Equivalences of an Imperative Class-based OO-language
No full textFickle is a class-based object oriented imperative language, which extends Java with object re- classification. In this paper, we introduce a natural observational equivalence on Fickle programs. This is a contextual equivalence on main methods with respect to a given sequence of class defini- tions, i.e. a program. To study it, we use the formal computational model for OO-programming based on coalgebras, which has recently emerged, whereby objects are taken to be equal when the actions of methods on them yield the same observations and equivalent next states. However, in order to deal with imperative features, we need to extend the original approach of H.Reichel and B.Jacobs in various ways. In particular, we introduce a coalgebraic description of objects (states of a class), which induces a coinductive behavioural equivalence on programs. For simplicity, we focus on Fickle objects whose methods do not take more than one object parameter as argument. Completeness results as well as problematic issues arising from binary methods are also discussed
Categories of Coalgebraic Games
No full textWe consider a general notion of coalgebraic game, whereby games are viewed as elements of a final coalgebra. This allows for a smooth definition of game operations (e.g. sum, negation, and linear implication) as final morphisms. The notion of coalgebraic game subsumes different notions of games, e.g. possibly non-wellfounded Conway games and games arising in Game Semantics à la [AJM00]. We define various categories of coalgebraic games and (total) strategies, where the above operations become functorial, and induce a structure of monoidal closed or*-autonomous category. In particular, we define a category of coalgebraic games corresponding to AJM-games and winning strategies, and a generalization to non-wellfounded games of Joyal's category of Conway games. This latter construction provides a categorical characterization of the equivalence by Berlekamp, Conway, Guy on loopy games
Strict Geometry of Interaction Graph Models
No full textWe study a class of "wave-style" Geometry of Interaction (Gol) λ-models based on the category Rel of sets and relations. Wave Gol models arise when Abramsky's Gol axiomatization, which generalizes Girard's original Gol, is applied to a traced monoidal category with the categorical product as tensor, using "countable power" as the traced strong monoidal functor!. Abramsky hinted that the category Rel is the basic setting for traditional denotational "static semantics". However, Rel, together with the cartesian product, apparently escapes Abramsky's original GoI construction. Here we show that Rel can be axiomatized as a strict GoI situation, i.e. a strict variant of Abramsky's Gol situation, which gives rise to a rich class of strict graph models. These are models of restricted λ-calculi in the sense of [HL99], such as Church's λ-I-calculus and the AβKN-calculus
Coalgebraic Description of Generalized Binary Methods
No full textWe extend the Reichel-Jacobs coalgebraic account of specification and refinement of objects and classes in Object Oriented Programming to (generalized) binary methods. These are methods that take more than one parameter of a class type. Class types include sums and (possibly infinite) products type constructors. We study and compare two solutions for modeling generalized binary methods, which use purely covariant functors. In the first solution, which applies when we already have a class implementation, we reduce the behaviour of a generalized binary method to that of a bunch of unary methods. These are obtained by freezing the types of the extra class parameters to constant types. The bisimulation behavioural equivalence induced on objects by this model amounts to the greatest congruence w.r.t method application. Alternatively, we treat binary methods as graphs instead of functions, thus turning contravariant occurrences in the functor into covariant ones
Going 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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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