1,720,958 research outputs found
Formal Verification of Digital Systems by Reduction of Data Paths
No full textVerification of properties (tasks) on a system P containing data paths may require too many resources (memory space and/or computation time) because such systems have very large and deep state spaces. As pointed out by Kurshan, what is needed is a reduced system P' which behaves exactly as P with respect to the properties that must be proved, but more compact than P, so that the verification can be easily performed. The process of finding P' from P is called reduction. P is specified by a network of interacting finite-state machines for data paths and controllers, and tasks are specified by finite-state automate. The verification of a task T on P is performed by the language containment check L(P)⊆L(T), where L(P) is the language generated by P and L(T) is the language accepted by T. It has been shown that, under appropriate conditions, the system P can be reduced to P' and the task T to T' such that L(P')⊆L(T')⇔L(P)⊆L(T). The direct language containment check L(P)⊆L(T) is no longer needed; it is replaced by L(P')⊆L(T'), which is less expensive. More specifically, for the purpose of simplifying the verification of some properties, the system implementation is abstracted locally with respect to the behavior under observation (i.e., bottom-up reduction), in the context of an integrated top-down design/verification technique. The tasks that one may want to verify can express both safety and fairness constraints. In this paper, we prove that the reduction of some data paths to four-state, nondeterministic finite-state machines, and the redundancy removal performed on the controllers is a homomorphic transformation, so that the simplified language containment check can automatically be applied without testing the validity of the homomorphism. This homomorphism correctness verification, required when a formal proof is not available, can be executed using a tool like Cospan, but it may not be completed when the state space to be traversed is too large and deep. The redundancy removal performed on the controllers is important because it eliminates the spurious behaviors introduced in the system by the nondeterminism of the reduced data paths. Redundancy, in fact, may induce a failure in the verification of L(P')⊆L(T'), while L(P)⊆L(T) actually holds. In order to show the effectiveness of the proposed methodology, we verify properties on an extended version of the Mead-Conway Traffic Light Controller, on a modified IRQ communication protocol, and on a relatively prime integers checker and generato
Algorithms for Approximate FSM Traversal Based on State SpaceDecomposition
No full textThis paper presents algorithms for approximate finite state machine traversal based on state space decomposition. The original finite state machine is partitioned in component submachines, and each of them is traversed separately; the result of the computation is an over-estimation of the set of reachable states of the original machine. Different traversal strategies, which reduce the effects of the degrees of freedom introduced by the decomposition, are discussed. Efficient partitioning is a key point for the performance of the traversal techniques; a method to heuristically find a good decomposition of the overall finite state machine, based on the exploration of its state variable dependency graph, is proposed. Applications of the approximate traversal methods to logic optimization of sequential circuits and behavioral verification of finite state machines are described; experimental results for such applications, together with data concerning pure traversal, are reporte
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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