• Journal of Internet Computing and Services
• /
• v.6 no.4
• /
• pp.59-73
• /
• 2005

Caching query results and reusing them in processing of subsequent queries is an important query optimization technique. Materialized view and view indexing are the representative examples of such a technique. The two schemes had received much attention for relational databases, and have been investigated for XML data since XML emerged as the standard for data exchange on the Web. In XML view indexing, XML view xv which is the result of an XML query is represented as an XML view index(XVI), a structure containing the identifiers of xv's underlying XML elements as well as the information on xv. Since XVI for xv stores just the identifiers of the XML elements not the elements themselves, when xv is requested, its XVI should be materialized against xv's underlying XML documents. In this paper, we address the problem of integrating an XML view index management system with an RDBMS based XML storage system. The proposed system was implemented in Java on Windows 2000 Server with each of two different commercial RDBMSs, and used in evaluating performance improvement through XML view indexing as well as its overheads. The experimental results revealed that XML view indexing was very effective with an RDBMS based XML storage system while its overhead was negligible.

• Journal of the Korean Society of Radiology
• /
• v.16 no.3
• /
• pp.295-302
• /
• 2022

Sparse-view computed tomography (CT) imaging technique is able to reduce radiation dose, ensure the uniformity of image characteristics among projections and suppress noise. However, the reconstructed images obtained by the sparse-view CT imaging technique suffer from severe artifacts, resulting in the distortion of image quality and internal structures. In this study, we proposed a convolutional neural network (CNN) with wavelet transformation and residual learning for reducing artifacts in sparse-view CT image, and the performance of the trained model was quantitatively analyzed. The CNN consisted of wavelet transformation, convolutional and inverse wavelet transformation layers, and input and output images were configured as sparse-view CT images and residual images, respectively. For training the CNN, the loss function was calculated by using mean squared error (MSE), and the Adam function was used as an optimizer. Result images were obtained by subtracting the residual images, which were predicted by the trained model, from sparse-view CT images. The quantitative accuracy of the result images were measured in terms of peak signal-to-noise ratio (PSNR) and structural similarity (SSIM). The results showed that the trained model is able to improve the spatial resolution of the result images as well as reduce artifacts in sparse-view CT images effectively. Also, the trained model increased the PSNR and SSIM by 8.18% and 19.71% in comparison to the imaging model trained without wavelet transformation and residual learning, respectively. Therefore, the imaging model proposed in this study can restore the image quality of sparse-view CT image by reducing artifacts, improving spatial resolution and quantitative accuracy.

• Journal of KIISE:Databases
• /
• v.28 no.2
• /
• pp.168-180
• /
• 2001

데이터 웨어하우스 시스템에 대한 OLAP 질의들은 대량의 데이터를 대상으로 복잡한 분석 및 집계 연산을 수행한다. 이러한 고비용의 OLAP 질의들을 효율적으로 실행하는 것은 시 스템의 성능 향상을 위해 매우 중요하다. 이를 위해 본 논문에서는 데이터 웨어하우스 시스 템에 존재하는 여러 종류의 실체 집계 뷰들을 이용하여 주어진 OLAP 질의를 재작성하는 방법을 제안한다. 본 논문에서는 차원 계층들로부터 유도되는 그룹 격자를 이용하여 OLAP 질의와 실체 뷰의 선택 단위, 선택 영역, 집계 단위등을 정의하고, 이들로부터 OLAP 질의 와 식체 뷰에 대한 정규을 정의한다. 그리고 정규형으로 표현된 질의와 실체 뷰 사이의 관 계를 이용하여 실체 뷰가 질의의 재작성에 이용 가능하기 위한 조건을 제시한다. 제안하는 질의 재작성 방법은 데이터 웨어하우스의 메타 정보들과 OLAP 질의 및 실체 뷰들의 특성 을 고려하여 다양한 실체 뷰들을 함께 이용할 수 있으므로, 시스템에 존재하는 실체 뷰들의 효용성을 높이고 주어진 질의를 효율적으로 처리할 수 있다.

• Journal of KIISE:Software and Applications
• /
• v.26 no.5
• /
• pp.604-612
• /
• 1999

데이터웨어하우스는 데이터분석을 위한 특수 목적의 데이터베이스로, 주로 데이터분석을 위한 질의(이하 OLAP 질의)가 던져진다. 그런데 OLAP질의는 수백만개의 레코드를 가지 테이블에 대해 하나 이상의 aggregation 함수와 group-by 연산자가 포함되므로, 질의 처리 시간은 수 분에서 수 시간이 걸린다. 이를 개선하기위하여 데이터 큐브를 구현함에 있어서의 문제는 디스크 공간이 한정되어 있기 때문에 평균 질의 처리 시간이 훨씬 짧아진다하더라도 모든 셀들을 실체화할수 없다. 따라서 한정된 디스크 공간을 최대한 활용하면서 가능한 빠른 평균 질의 처리 시간을 얻을 수 있도록 데이터 큐브의 일부만을 실체화 시켜야한다. 본 논문의 주제와 관련된 연구로는 Harinarayan[4] 이 제안한 greedy 알고리즘이 있다. 이 알고리즘은 1) 데이터 큐브를 격자구조로 표현한후, 2) 격자의 위에서부터 아래로 차례로 뷰들을 방문하면서 방문한 뷰가 실체화되 경우 데이터 큐브에 주는 이익을 계산한다. 3) 그 중 가장 이익이 큰 것을 선택한다. 3) 그중 가장 이익이 큰 것을 선택한다. 2)와 3)의 과정은 k개의 뷰를 선택할 경우, k번 반복된다. 이 알고리즘의 운영 시간은 데이터 큐브를 구성하는 뷰의 개수가 n개이고 그 중에서 k개를 실체화할 경우에 O(kn2)이다. 본 논문에서는 운영 시간을 향상시킨 수정된 greedy 알고리즘을 제안한다. 알고리즘 내부에서 실체화할 뷰를 선택할 때 격자를 단순화시킨 트리를 사용함으로써, 알고리즘 운영시간을 O(kn2)에서 O(kn)으로 향상시켰다.

• Proceedings of the Korea Contents Association Conference
• /
• 2009.05a
• /
• pp.74-78
• /
• 2009

Efficient reasoning has become important for improving the performance of ontology systems as the size of ontology grows. In this paper, we introduce a method that efficiently performs reasoning of RDFS entailment rules (i.e., rdfs7 and rdfs9 rules) and OWL inverse rule using views in the DBMS-based triple sotre. Reasoning is performed by replacing reasoning rules with the corresponding view definition and storing RDF triples into the structured triple tables. When processing queries, the views is referred instead of original tables. In this way, we can reduce the time needed for reasoning and also obtain the space-efficiency of the triple store.

• The KIPS Transactions:PartD
• /
• v.10D no.2
• /
• pp.221-232
• /
• 2003

This paper addresses the query processing component of a wrapper system for a relational database model based on the XML view in integrating databases. The schema of a relational database is represented as XML Schema that is proposed by W3C. Users submit a query using the XML query language XQuery over the XML Schema. The wrapper system to be developed supports an user-defined XML view. XQuery is also used as the view definition language. In this environment, this paper suggests a new XML query processing model. We propose the composition algorithm of an XML view with an user query, the translation algorithm of XQuery into SQL, and the XML template construction algorithm for generating XML documents.

• The KIPS Transactions:PartD
• /
• v.11D no.4
• /
• pp.765-774
• /
• 2004

In order to integrate heterogeneous biological information sources, it is necessary to define the view that represents unified viewpoint for the multiple sources by hiding heterogeneity of the data. We present an XML-based view definition model and show Its operating principles in designing the middleware system to integrate biological information sources. This model supports the user-defined XML view to increase flexibility in constructing the integration system and execute integrated queries on higher level ion. Based on the view-definition model, we present a wrapping model for relational database systems and web resources as well as an application program.

• Journal of Broadcast Engineering
• /
• v.25 no.5
• /
• pp.770-775
• /
• 2020

Since 360-degree ERP frame structure has location-dependent distortion, existing video surveillance algorithms cannot be applied to 360-degree video. In this paper, an activated viewport based event detection method is proposed for 360-degree video. After extracting activated viewports enclosing object candidates, objects are finally detected in the viewports. These objects are tracked in 360-degree video space for region-based event detection. The proposed method is shown to improve the recall and the false negative rate more than 30% compared to the conventional method without activated viewports.

• The KIPS Transactions:PartD
• /
• v.11D no.3
• /
• pp.553-562
• /
• 2004

This paper constructs ERD thesaurus that is storing information about Entity Relationship Diagram(ERD), and proposes an ERD thesaurus-based methodology for view integration in an important conceptual design step in designing databases. To show the usefulness of proposed methodology, the prototype for view integration support system is implemented for the applied case. As a result, ERD thesaurus-based methodology is more effective than the existing methodologies for view Integration in the aspects of affinity analysis, semantic conflicts resolution, and view Integration processes. Therefore, our methodology is expected to be utilized in integrating the existing fragmented schema or designing a large database integration.

• Journal of KIISE:Databases
• /
• v.28 no.4
• /
• pp.620-632
• /
• 2001

This paper proposes a mediator system which can provide a view management function in the today's heterogeneous computing environment including operating system database management systems and other software. while most mediators use view modification mechanism only, the use of view materialization is also considered in this research. In order to optimize the management cost for materialized views the proposed method applies a decay factor for modeling the access behaviors of views In other words, the most recently access pattern gets the highest attention in the optimization process all the necessary it with the CORBA.