1,720,994 research outputs found
An aggregation algorithm using a multidimensional file in multidimensional OLAP
No full textAggregation is an operation that plays a key role in multidimensional OLAP (MOLAP). Existing aggregation methods in MOLAP have been proposed for file structures such as multidimensional arrays. These file structures are suitable for data with uniform distributions, but do not work well with skewed distributions. In this paper, we consider an aggregation method that uses dynamic multidimensional files adapting to skewed distributions. In these multidimensional files, the sizes of page regions vary according to the data density in these regions, and the pages that belong to a larger region are accessed multiple times while computing aggregations. To solve this problem, we first present an aggregation computation model that uses the new notions of disjoint-inclusive partition and induced space filling curves. Based on this model, we then present a dynamic aggregation algorithm. Using these notions, the algorithm allows us to maximize the effectiveness of the buffer-we control the page access order in such a way that a page being accessed can reside in the buffer until the next access. We have conducted experiments to show the effectiveness of our approach. Experimental results for a real data set show that the algorithm reduces the number of disk accesses by up to 5.09 times compared with a naive algorithm. The results further show that the algorithm achieves a near optimal performance (i.e., normalized I/O = 1.01) with the total main memory (needed for the buffer and the result table) less than 1.0% of the database size. We believe our work also provides an excellent formal basis for investigating further issues in computing aggregations in MOLAR (C) 2003 Published by Elsevier Science Inc
RNA-stimulated ATPase and RNA helicase activities and RNA binding domain of hepatitis G virus nonstructural protein 3
No full textHepatitis G virus (HGV) nonstructural protein 3 (NS3) contains amino acid sequence motifs typical of ATPase and RNA helicase proteins. In order to examine the RNA helicase activity of the HGV NS3 protein, the NS3 region (amino acids 904 to 1580) was fused with maltose-binding protein (MBP), and the fusion protein was expressed in Escherichia coli and purified with amylose resin and anion-exchange chromatography. The purified MBP-HGV/NS3 protein possessed RNA-stimulated ATPase and RNA helicase activities. Characterization of the ATPase and RNA helicase activities of MBP-HGV/NS3 showed that the optimal reaction conditions were similar to those of other Flaviviridae viral NS3 proteins. However, the kinetic analysis of NTPase activity showed that the MBP-HGV/NS3 protein had several unique properties compared to the other Flaviriridae NS3 proteins. The HGV NS3 helicase unwinds RNA-RNA duplexes in a 3'-to-5' direction and can unwind RNA-DNA heteroduplexes and DNA-DNA duplexes as well. In a gel retardation assay, the MBP-HGV/ NS3 helicase bound to RNA, RNA/DNA, and DNA duplexes with 5' and 3' overhangs but not to blunt-ended RNA duplexes. We also found that the conserved motif VI was important for RNA binding. Further deletion mapping showed that the RNA binding domain was located between residues 1383 and 1395, QRRGRT-GRGRSGR, Our data showed that the MBP-HCV/NS3 protein also contains the RNA binding domain in the similar domain
Transform-space view: Performing spatial join in the transform space using original-space indexes
No full textSpatial joins find all pairs of objects that satisfy a given spatial relationship. In spatial joins using indexes, original-space indexes such as the R-tree are widely used. An original-space index is the one that indexes objects as represented in the original space. Since original-space indexes deal with extents of objects, it is relatively complex to optimize join algorithms using these indexes. On the other hand, transform-space indexes, which transform objects in the original space into points in the transform space and index them, deal only with points but no extents. Thus, optimization of join algorithms using these indexes can be relatively simple. However, the disadvantage of these join algorithms is that they cannot be applied to original-space indexes such as the R-tree; In this paper, we present a novel mechanism for achieving the best of these two types of algorithms. Specifically, we propose the new notion of the transform-space view and present the transform-space view join algorithm. The transform-space view is a virtual transform-space index based on an original-space index. It allows us to "interpret" or "view" an existing original-space index as a transform-space index with no space and negligible time overhead and without actually modifying the structure of the original space index or changing object representation. The transform-space view join algorithm joins two original-space indexes in the transform space through the notion of the transform-space view. Through analysis and experiments, we verify the excellence of the transform-space view join algorithm. The transform-space view join algorithm always outperforms existing ones for all the data sets tested in terms of all three measures used: the one-pass buffer size (the minimum buffer size required for guaranteeing one disk access per page), the number of disk accesses for a given buffer size, and the wall clock time. Thus, it constitutes a lower-bound algorithm. We believe that the proposed transform-space view can be applied to developing various new spatial query processing algorithms in the transform space
Adaptive row major order: a new space filling curve for efficient spatial join processing in the transform space
No full textA transform-space index indexes spatial objects represented as points in the transform space. An advantage of a transform-space index is that optimization of spatial join algorithms using these indexes can be more formal. The authors earlier proposed the Transform-Based Spatial Join algorithm that joins two transform-space indexes. It renders global optimization easy with little overhead by utilizing the characteristics of the transform space. In particular, it allows us to globally determine the order of accessing disk pages, which makes a significant impact on the performance of joins. For this purpose, we use various space filling curves. In this paper, we propose a new space filling curve called the adaptive row major order (ARM order). The ARM order adaptively controls the order of accessing pages and significantly reduces the one-pass buffer Size (the minimum buffer size required for guaranteeing one disk access per page) and the number of disk accesses for a given buffer size. Through analysis and experiments, we verify excellence of the ARM order when used with the Transform-Based Spatial Join. The Transform-Based Spatial Join with the ARM order always outperforms those with other conventional space filling curves in terms of both measures used: the one-pass buffer size and the number of disk accesses. Specifically, it reduces the one-pass buffer size by up to 25.9 times and the number of disk accesses by up to 2.11 times. We conclude that we achieve these results mainly due to global optimization of the order of accessing disk pages using an adaptive space filling curve. (c) 2004 Elsevier Inc. All rights reserved
A physical database design method for multidimensional file organizations
No full textThis paper presents a physical database design methodology for multidimensional file organizations. Physical database design is the process of determining the optimal configuration of physical files and access structures for a given set of queries. Recently, many multidimensional file organizations have been proposed in the literature. However, there has been no effort toward their physical database design. We first show that the performance of query processing is highly affected by the similarity between the shapes of query regions and page regions in the domain space, and then propose a method for finding the optimal configuration of the multidimensional file by controlling the interval ratio of different axes to achieve the similarity. For performance evaluation, we perform extensive experiments with the multilevel grid file, a multidimensional file organization, using various types of queries and record distributions. The results indicate that our proposed method builds optimal multilevel grid files regardless of the query types and record distributions. When the interval ratio of a two-dimensional query region is 1:1024, the performance of the proposed method is enhanced by as much as 7.5 times over that of the conventional method that has an interval ratio of 1:1 employing the cyclic splitting strategy. The performance is further enhanced for query types having higher interval ratios. The result is significant since interval ratios can be far from 1:1 for many practical applications, especially when different axes have different domains. (C) Elsevier Science Inc. 1997
A conflict detection mechanism for authorization using intention types in object-oriented database systems
No full textMany object-oriented database systems have used the notion of implicit authorization to avoid the overhead caused by explicitly storing all authorizations for each object. In implicit authorization, it is very important to detect efficiently conflicts between existing authorizations and new authorizations to be added. In this article we propose a conflict detection mechanism in the OODBMSs using implicit authorization with the notion of intention type authorization. When Lye grant an authorization on a node n in the database granularity hierarchy, the existing method is inefficient in determining the conflicts since it needs to examine all authorizations on the descendants of the node n. In contrast, our mechanism has the advantage of detecting the conflicts at the node n where an explicit authorization is to be granted without examining any authorizations below the node n. Thus, the proposed mechanism can detect a conflict with the average time complexity of O(d), which is smaller than O(m(d)) of existing methods, where m is the number of children nodes at an arbitrary level and d is the difference of levels between the node with an existing explicit authorization and the higher node where an explicit authorization is to be granted. We also show that the additional storage overhead of storing all authorizations is negligible when compared with the total number of all explicit authorizations
A tunable class hierarchy index for object-oriented databases using a multidimensional index structure
No full textThis paper presents a tunable two-dimensional class hierarchy indexing technique (2D-CHI) for object-oriented databases. We use a two-dimensional file organization as the index structure. 2D-CHI deals with the problem of clustering objects in a two-dimensional domain space consisting of the key attribute domain and the class identifier domain. In conventional class indexing techniques using one-dimensional index structures such as the B+-tree, the clustering property is owned exclusively by one attribute. These indexing techniques do not handle the queries that address both the attribute keys and the class identifiers efficiently. 2D-CHI enhances query performance by adjusting the degree of clustering between the key value domain and the class identifier domain based on the precollected usage pattern. For performance evaluation, we first compare 2D-CHI with the conventional class indexing techniques using an analytic cost model based on the assumption of uniform object distribution, and then, verify the cost model through experiments using the multilevel grid file as the two-dimensional index. We further perform experiments with nonuniform object distributions. The experiments show that our proposed method builds optimal class index structures in terms of the total number of page accesses for given the precollected usage pattern regardless of query types and object distributions. (C) 2001 Elsevier Science B.V. All rights reserved
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
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