1,721,015 research outputs found
Graded-CTL: Satisfiability and Symbolic Model Checking
No full textIn this paper we continue the study of a strict extension of the Computation Tree Logic, called `graded-CTL`, recently introduced by the same authors in [FNP08]. This new logic augments the standard quantifiers with graded modalities, being able thus to express `There exist at least k` or `For all but k` futures, for some constant k. One can thus describe properties useful in system design, which cannot be expressed with CTL, like a sort of redundant liveness property asking whether there is more than one path satisfying that `something good eventually happens`, making thus the system more tolerant to possible faults. Graded-CTL formulas can also be used to determine whether there are more than a given number of bad behaviors of a system: this, in the model-checking framework, means that one can verify the existence of a user-defined number of counterexamples for a given specification and generate them, in a unique run of the model-checker. Here we show both theoretical and applicative contributions. On the theoretical side we give a simple algorithm to `decide` this logic and we prove that the satisfiability problem is ExpTime-complete when the constants of the quantifiers are represented in unary. On the applicative side we propose `symbolic` algorithms to solve the model checking problem. One of the main characteristics of these algorithms is that, though the the computation of `distinct` counterexamples has inherently high complexity when the model is represented symbolically (consider for example the implementation of a symbolic DFS), we have designed them to make the generation of multiple counterexamples as easy and quick as possible. The symbolic algorithms have also been implemented using BDD data structures, and have been integrated into the well known NuSMV model checker, that has also been modified to accept specifications expressed in graded-CTL. The test results we have reported are very comfortable in the sense that both the running time and the sizes of the BDD produced are comparable to those obtained with specifications expressed in classical CTL
MODEL-CHECKING FOR GRADED CTL
No full textRecently, complexity issues related to the decidability of the -calculus, when the universal and existential quantifiers are augmented with `graded modalities`, have been investigated by Kupfermann, Sattler and Vardi ([KSV02]). Graded modalities refer to the use of the universal and existential quantifiers with the added capability to express the concept of `at least` or `all but` , for a non-negative integer . In this paper we study the Computational Tree Logic CTL, a branching time extension of classical modal logic, augmented with graded modalities and investigate the complexity issues with respect to the model-checking problem. We consider a system model represented by a Kripke structure and give an algorithm to solve the model-checking problem running in time which is hence tight for the problem (here is the number of temporal and boolean operators and does not include the values occurring in the graded modalities). In this framework, the graded modalities express the ability to generate a user-defined number of counterexamples to a specification given in \ctl. However, these multiple counterexamples can partially overlap, that is they may share some behavior. We have hence investigated the case when all of them are completely disjoint. In this case we prove that the model-checking problem is both \NP-hard and \coNP-hard and give an algorithm for solving it running in polynomial space. We have thus studied a fragment of graded-\ctl, and have proved that the model-checking problem is solvable in polynomial time
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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