• Title, Summary, Keyword: Aggregation Query

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SPEC: Space Efficient Cubes for Data Warehouses (SPEC : 데이타 웨어하우스를 위한 저장 공간 효율적인 큐브)

  • Chun Seok-Ju;Lee Seok-Lyong;Kang Heum-Geun;Chung Chin-Wan
    • Journal of KIISE:Databases
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    • v.32 no.1
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    • pp.1-11
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    • 2005
  • An aggregation query computes aggregate information over a data cube in the query range specified by a user Existing methods based on the prefix-sum approach use an additional cube called the prefix-sum cube(PC), to store the cumulative sums of data, causing a high space overhead. This space overhead not only leads to extra costs for storage devices, but also causes additional propagations of updates and longer access time on physical devices. In this paper, we propose a new prefix-sum cube called 'SPEC' which drastically reduces the space of the PC in a large data warehouse. The SPEC decreases the update propagation caused by the dependency between values in cells of the PC. We develop an effective algorithm which finds dense sub-cubes from a large data cube. We perform an extensive experiment with respect to various dimensions of the data cube and query sizes, and examine the effectiveness and performance ot our proposed method. Experimental results show that the SPEC significantly reduces the space of the PC while maintaining a reasonable query performance.

Normalization of XQuery Queries for Efficient XML Query Processing (효율적인 XML질의 처리를 위한 XQuery 질의의 정규화)

  • 김서영;이기훈;황규영
    • Journal of KIISE:Computing Practices and Letters
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    • v.10 no.5
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    • pp.419-433
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    • 2004
  • As XML becomes a standard for data representation, integration, and exchange on the Web, several XML query languages have been proposed. World Wide Web Consortium(W3C) has proposed XQuery as a standard for the XML query language. Like SQL, XQuery allows nested queries. Thus, normalization rules have been proposed to transform nested XQuery queries to semantically equivalent ones that could be executed more efficiently. However, previous normalization rules are applicable only to restricted forms of nested XQuery queries. Specifically, they can not handle FLWR expressions having nested expressions in the where clause. In this paper, we propose normalization rules for XQuery queries by extending those for SQL queries. Our proposed rules can handle FLWR expressions haying nested expressions in every clause. The major contributions of this paper are as follows. First, we classily nesting types of XQuery queries according to the existence of correlation and aggregation. We then propose normalization rules for each nesting type. Second, we propose detailed algorithms that apply the normalization rules to nested XQuery queries.

Spanning Tree Aggregation Using Attribute of Service Boundary Line (서비스경계라인 속성을 이용한 스패닝 트리 집단화)

  • Kwon, So-Ra;Jeon, Chang-Ho
    • The KIPS Transactions:PartC
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    • v.18C no.6
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    • pp.441-444
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    • 2011
  • In this study, we present a method for efficiently aggregating network state information. It is especially useful for aggregating links that have both delay and bandwidth in an asymmetric network. Proposed method reduces the information distortion of logical link by integration process after similar measure and grouping of logical links in multi-level topology transformation to reduce the space complexity. It is applied to transform the full mesh topology whose Service Boundary Line (SBL) serves as its logical link into a spanning tree topology. Simulation results show that aggregated information accuracy and query response accuracy are higher than that of other known method.

Ontology Versions Management Schemes using Change Set (변경 집합을 이용한 온톨로지 버전 관리 기법)

  • Yun, Hong-Won;Lee, Jung-Hwa;Kim, Jung-Won
    • Journal of Information Technology Applications and Management
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    • v.12 no.3
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    • pp.27-39
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    • 2005
  • The Semantic Web has increased the interest in ontologies recently Ontology is an essential component of the semantic web and continues to change and evolve. We consider versions management schemes in ontology. We study a set of changes based on domain changes, changes in conceptualization, metadata changes, and temporal dimension. Our change specification is represented by a set of changes. A set of changes consists of instance data change, structural change, and identifier change. In order to support a query in ontology versions, we consider temporal dimension includes valid time. Ontology versioning brings about massive amount of versions to be stored and maintained. We present the ontology versions management schemes that are 1) storing all the change sets, 2) storing the aggregation of change sets periodically, and 3) storing the aggregation of change sets using an adaptive criterion. We conduct a set of experiments to compare the performance of each versions management schemes. We present the experimental results for evaluating the performance of the three version management schemes from scheme 1 to scheme 3. Scheme 1 has the least storage usage. The average response time in Scheme 1 is extremely large, those of Scheme 3 is smaller than Scheme 2. Scheme 3 shows a good performance relatively.

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A Physical Design Method of Storage Structures for MOLAP Systems of Data Warehouse (데이터 웨어하우스의 다차원 온라인 분석처리 시스템을 위한 저장구조의 물리적 설계기법)

  • Lee Jong-Hak
    • Journal of Korea Multimedia Society
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    • v.8 no.3
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    • pp.297-312
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    • 2005
  • Aggregation is an operation that plays a key role in multidimensional OLAP (MOLAP) systems of data warehouse. Existing aggregation operations in MOLAP have been proposed for file structures such as multidimensional arrays. These tile structures do not work well with skewed distributions. This paper presents a physical design methodology for storage structures ni MOLAP that use the multidimensional tile organizations adapting to a skewed distribution. In uniform data distribution, we first show that the performance of multidimensional analytical processing is highly affected by the similarity of the shapes between query regions and page regions in the domain space of the multidimensional file organizations. And than, in skewed distributions, we reflect the effect of data distributions on the design by using the shapes of the normalized query regions that are weighted with data density of those query regions. Finally, we demonstrate that the physical design methodology theoretically derived is indeed correct in real environments. In the two-dimensional file organizations, the results of experiments indicate that the performance of the proposed method is enhanced by more than seven times over the conventional method. We expect that the performance will be more enhanced when the dimensionality is more than two. The result confirms that the proposed physical design methodology is useful in a practical way.

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Fast, Flexible Text Search Using Genomic Short-Read Mapping Model

  • Kim, Sung-Hwan;Cho, Hwan-Gue
    • ETRI Journal
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    • v.38 no.3
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    • pp.518-528
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    • 2016
  • The searching of an extensive document database for documents that are locally similar to a given query document, and the subsequent detection of similar regions between such documents, is considered as an essential task in the fields of information retrieval and data management. In this paper, we present a framework for such a task. The proposed framework employs the method of short-read mapping, which is used in bioinformatics to reveal similarities between genomic sequences. In this paper, documents are considered biological objects; consequently, edit operations between locally similar documents are viewed as an evolutionary process. Accordingly, we are able to apply the method of evolution tracing in the detection of similar regions between documents. In addition, we propose heuristic methods to address issues associated with the different stages of the proposed framework, for example, a frequency-based fragment ordering method and a locality-aware interval aggregation method. Extensive experiments covering various scenarios related to the search of an extensive document database for documents that are locally similar to a given query document are considered, and the results indicate that the proposed framework outperforms existing methods.

Tracking Moving Objects Using Signature-based Data Aggregation in Sensor Network (센서네트워크에서 시그니처 기반 데이터 집계를 이용한 이동객체 트래킹 기법)

  • Kim, Yong-Ki;Kim, Young-Jin;Yoon, Min;Chang, Jae-Woo
    • Journal of Korea Spatial Information System Society
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    • v.11 no.2
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    • pp.99-110
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    • 2009
  • Currently, there are many applications being developed based on sensor network technology. A tracking method for moving objects in sensor network is one of the main issue of this field. There is a little research on this issue, but most of the existing work has two problems. The first problem is a communication overhead for visiting sensor nodes many times to track a moving object. The second problem is an disability for dealing with many moving objects at a time. To resolve the problems, we, in this paper, propose a signature-based tracking method using efficient data aggregation for moving objects, called SigMO-TRK. For this, we first design a local routing hierarchy tree to aggregate moving objects' trajectories efficiently by using a space filtering technique. Secondly, we do the tracking of all trajectories of moving objects by using signature in a efficient way, our approach generates signatures to method. In addition, by extending the SigMO-TRK, we can retrieve the similar trajectories of moving objects for given a query. Finally, by using the TOSSIM simulator, we show that our signature-based tracking method outperforms the existing tracking method in terms of energy efficiency.

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An Energy-Efficient In-Network Join Query Processing using Synopsis and Encoding in Sensor Network (센서 네트워크에서 시놉시스와 인코딩을 이용한 에너지 효율적인 인-네트워크 조인 질의 처리)

  • Yeo, Myung-Ho;Jang, Yong-Jin;Kim, Hyun-Ju;Yoo, Jae-Soo
    • The Journal of the Korea Contents Association
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    • v.11 no.2
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    • pp.126-134
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    • 2011
  • Recently, many researchers are interested in using join queries to correlate sensor readings stored in different regions. In the conventional algorithm, the preliminary join coordinator collects the synopsis from sensor nodes and determines a set of sensor readings that are required for processing the join query. Then, the base station collects only a part of sensor readings instead of whole readings and performs the final join process. However, it has a problem that incurs communication overhead for processing the preliminary join. In this paper, we propose a novel energy-efficient in-network join scheme that solves such a problem. The proposed scheme determines a preliminary join coordinator located to minimize the communication cost for the preliminary join. The coordinator prunes data that do not contribute to the join result and performs the compression of sensor readings in the early stage of the join processing. Therefore, the base station just collects a part of compressed sensor readings with the decompression table and determines the join result from them. In the result, the proposed scheme reduces communication costs for the preliminary join processing and prolongs the network lifetime.

Spatio-Temporal Data Warehouses Using Fractals (프랙탈을 이용한 시공간 데이터웨어하우스)

  • 최원익;이석호
    • Proceedings of the Korean Information Science Society Conference
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    • pp.46-48
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    • 2003
  • 최근 시공간 데이타에 대한 OLAP연산 효율을 증가시키기 위한 여러 가지 연구들이 행하여지고 있다. 이들 연구의 대부분은 다중트리구조에 기반하고 있다. 다중트리구조는 공간차원을 색인하기 위한 하나의 R-tree와 시간차원을 색인하기 위한 다수의 B-tree로 이루어져 있다. 하지만, 이러한 다중트리구조는 높은 유지비용과 불충분한 질의 처리 효율로 인해 현실적으로 시공간 OLAP연산에 적용하기에는 어려운 점이 있다. 본 논문에서는 이러한 문제를 근본적으로 개선하기 위한 접근 방법으로서 힐버트큐브(Hilbert Cube, H-Cube)를 제안하고 있다. H-Cube는 집계질의(aggregation query) 처리 효율을 높이기 위해 힐버트 곡선을 이용하여 셀들에게 완전순서(total-order)를 부여하고 있으며, 아울러 전통적인 누적합(prefix-sum) 기법을 함께 적용하고 있다. H-Cube는 적응적이며, 완전순서화되어 있으며, 또한 누적합을 이용한 셀 기반의 색인구조이다. 본 논문에서는 H-Cube의 성능 평가를 위해서 다양한 실험을 하였으며, 그 결과로서 유지비용과 질의 처리 효율성면 모두에서 다중트리구조보다 높은 성능 향상이 있음을 보인다.

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Energy-Efficient In-Network Aggregation Query Processing in Sensor Networks with Multiple Sinks (센서 네트워크에서 다중 기지국을 고려한 에너지 효율적인 인-네트워크 병합 질의 처리)

  • Lee, Hyo-Joon;Yeo, Myung-Ho;Kim, Hak-Sin;Yoo, Jae-Soo
    • Proceedings of the Korea Information Processing Society Conference
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    • pp.789-790
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    • 2009
  • 본 논문은 인-네트워크 병합 질의를 처리하는 다중 기지국 센서 네트워크에서 데이터 변동률을 고려하지 않은 경우의 문제점을 분석한다 또한 데이터 변동률과 기지국과의 거리를 고려한 새로운 인-네트워크 병합 질의 처리 기법을 제안하였다. 성능 평가를 통해 제안하는 기법이 기존 기법 우수한 성능을 보인다. 실험 결과, 제안하는 기법이 불필요한 데이터 전송을 최대 32% 감소시켰다.

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