1,720,985 research outputs found
A unifying approach to evaluating block accesses in database organizations
No full textA nonrecursive discrete density function to compute the probability of retrieving k records from exactly i blocks of a file is introduced here. This function is shown to be equivalent to Siler's recursive one. Furthermore, we prove that Yao's formula is the expected value of our (and Siler's) probability function. © 1988
A method for hierarchy processing in relational systems
No full textProcessing of hierarchies has always been a difficult task in relational database environments. Several approaches have been proposed, but they have focused their attention mostly on improving the semantic power of relational systems in order to express recursive definitions on hierarchies rather than propose feasible computing methods. In this paper we show an encoding method which allows us to cope with one-to-many hierarchical relationships in a very different way. The novel idea is not to store the key of the parent tuple but create a code for the path of all the ancestor tuples. Two major advantages are thus obtained: a considerable reduction in the retrieval of unnecessary intermediate tuples, and an enrichment of the information that is utilized by the optimizer module to choose the best access strategy. © 1989
Declustering of Key-Based Partitioned Signature Files
No full textAccess methods based on signature files can largely benefit from possibilities offered by parallel environments. To this end, an effective declustering strategy that would distribute signatures over a set of parallel independent disks has to be combined with a synergic clustering which is employed to avoid searching the whole signature file while executing a query. This article proposes two parallel signature file organizations, Hamming Filter (HF) and Hamming+ Filter (H+F), whose common declustering strategy is based on error correcting codes, and where clustering is achieved by organizing signatures into fixed-size buckets, each containing signatures sharing the same key value. HF allocates signatures on disks in a static way and works well if a correct relationship holds between the parameters of the code and the size of the file. H+F is a generalization of HF suitable to manage highly dynamic files. It uses a dynamic declustering, obtained through a sequence of codes, and organizes a smooth migration of signatures between disks so that high performance levels are retained regardless of current file size. Theoretical analysis characterizes the best-case, expected, and worst-case behaviors of these organizations. Analytical results are verified by experiments on prototype systems
Key-Based Partitioned Bit-Sliced Signature File
No full textA new signature file organization is proposed as a combination of two orthogonal partitioning strategies, the key-based and the bit-sliced, respectively. The design results from theoretical analysis of these elementary approaches in which performance is analytically studied respecting a simplified abstract storage structure model. The new organization is able to achieve very high search performance for queries containing arbitrary number of query terms - bit-sliced (key-based) organization is good only for queries containing few (many) terms, quite bad performance is obtained in the other cases. Update performance is also discussed and a generalization of the method, able to adjust the trade-off between the search efficiency and the maintenance costs, is put forward for consideration. The proposal is also compared with similar approaches in the field of signature files. © 1995, ACM. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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