• International Journal of Contents
• /
• 제3권2호
• /
• pp.6-17
• /
• 2007

Emerging modem database applications require multi-dimensional index structures to provide high performance for data retrieval. In order for a multi-dimensional index structure to be integrated into a commercial database system, efficient techniques that provide transactional access to data through this index structure are necessary. The techniques must support all degrees of isolation offered by the database system. Especially degree 3 isolation, called "no phantom read," protects search ranges from concurrent insertions and the rollbacks of deletions. In this paper, we propose a new phantom protection method for multi-dimensional index structures that uses a multi-level grid technique. The proposed mechanism is independent of the type of the multi-dimensional index structure, i.e., it can be applied to all types of index structures such as tree-based, file-based, and hash-based index structures. In addition, it has a low development cost and achieves high concurrency with a low lock overhead. It is shown through various experiments that the proposed method outperforms existing phantom protection methods for multi-dimensional index structures.

• ETRI Journal
• /
• 제22권2호
• /
• pp.32-42
• /
• 2000

The existing multi-dimensional index structures are not adequate for indexing higher-dimensional data sets. Although conceptually they can be extended to higher dimensionalities, they usually require time and space that grow exponentially with the dimensionality. In this paper, we analyze the existing index structures and derive some requirements of an index structure for content-based image retrieval. We also propose a new structure, for indexing large amount of point data in a high-dimensional space that satisfies the requirements. in order to justify the performance of the proposed structure, we compare the proposed structure with the existing index structures in various environments. We show, through experiments, that our proposed structure outperforms the existing structures in terms of retrieval time and storage overhead.

• Computers and Concrete
• /
• 제31권3호
• /
• pp.241-252
• /
• 2023

Corrosion of rebar is one of the major deteriorating mechanisms that affect the durability of reinforced concrete (RC) structures. The increase in CO₂ concentration in the atmosphere leads to early carbonation and deterioration due to corrosion in RC structures. In the present study, an attempt has been made to modify the existing carbonation depth prediction empirical model. The modified empirical model is verified from the carbonation data collected from selected RC structures of CSIR-SERC campus, Chennai and carbonation data available from the reported literature on in-situ RC structures. Attempt also made to study the carbonation depth in the laboratory specimens using oxygen permeability index (OPI) test. The carbonation depth measured from RC structures and laboratory specimens are compared with estimated carbonation depth obtained from OPI test data. The modified empirical model shows good correlation with measured carbonation depth from the identified RC structures and the reported RC structures from the literature. The carbonation depth estimated from OPI values for both in-situ and laboratory specimens show lesser percentage of error compared to measured carbonation depth. From the present investigation it can be said that the OPI test is the suitable test method for both new and existing RC structures and laboratory RC specimens.

• Smart Structures and Systems
• /
• 제20권4호
• /
• pp.427-440
• /
• 2017

One of the suitable structural damage detection methods using vibrational characteristics are damage-index-based methods. In this study, a damage index for identifying damages in plate structures using frequency response function (FRF) data has been provided. One of the significant challenges of identifying the damages in plate structures is high number of degrees of freedom resulting in decreased damage identifying accuracy. On the other hand, FRF data are of high volume and this dramatically decreases the computing speed and increases the memory necessary to store the data, which makes the use of this method difficult. In this study, FRF data are compressed using two-dimensional principal component analysis (2D-PCA), and then converted into damage index vectors. The damage indices, each of which represents a specific condition of intact or damaged structures are stored in a database. After computing damage index of structure with unknown damage and using algorithm of lookup tables, the structural damage including the severity and location of the damage will be identified. In this study, damage detection accuracy using the proposed damage index in square-shaped structural plates with dimensions of 3, 7 and 10 meters and with boundary conditions of four simply supported edges (4S), three clamped edges (3C), and four clamped edges (4C) under various single and multiple-element damage scenarios have been studied. Furthermore, in order to model uncertainties of measurement, insensitivity of this method to noises in the data measured by applying values of 5, 10, 15 and 20 percent of normal Gaussian noise to FRF values is discussed.

• 정보처리학회논문지D
• /
• 제13D권3호
• /
• pp.325-336
• /
• 2006

최근 LBS(location-based service)를 지원하기 위해, 공간 네트워크를 고려한 연구가 활발히 수행 중에 있다. 본 논문에서는 공간 네트워크 데이터베이스에서의 우수한 질의처리 성능을 위해, 공간 네트워크상에 존재하는 공간 네트워크 자체의 데이터, POI(point of interest), 이동객체 데이터를 위한 효율적인 저장 및 색인 구조를 설계한다. 이를 위해 첫째, 노드와 에지로 구성된 공간 네트워크 자체의 데이터를 관리하기 위해 공간 네트워크 파일 구조를 설계한다. 둘째, 식당, 호텔, 주유소와 같은 POI에 대한 효율적인 접근을 위해 POI 저장 및 색인 구조를 설계한다. 셋째 이동객체의 과거, 현재, 미래 궤적 정보를 효과적으로 관리하기 위해 시그니쳐 기반 저장 및 색인 구조를 설계한다. 마지막으로, 본 논문에서 설계한 저장 및 색인 구조가 기존의 공간 네트워크를 위한 저장구조 및 이동객체를 위한 궤적 색인구조 보다 성능이 우수함을 보인다.

• 정보기술과데이타베이스저널
• /
• 제8권2호
• /
• pp.103-114
• /
• 2001

In this paper, we propose an efficient index mechanism for real-time main memory database systems. Existing main memory index structures based on the tree can effectively support range searches. However, it doesn't guarantee the real-time characteristic because difference between the access time of a node and an average access time can be high. The index structures based on the hash have always a regular random access time on the simple searches and that speed is very fast. However they do not support range searches. To solve such problems, we propose a new index mechanism called Hyper Tree-Hash (Hyper-TH) that combines ECBH (Extendible Chained Bucket Hashing) and T＊-tree. ECBH can be dynamically extended and has a very fast access time. T＊-tree effectively supports the range searches. We show through our experiments that the proposed mechanism outperforms existing other index structures.

• Smart Structures and Systems
• /
• 제20권2호
• /
• pp.115-126
• /
• 2017

The modal identification of large civil structures such as bridges under the ambient vibrational conditions has been widely investigated during the past decade. Many operational modal analysis methods have been proposed and successfully used for identifying the dynamic characteristics of the constructed bridges in service. However, there is very limited research available on reliable criteria for the robustness of these identified modal parameters of the bridge structures. In this study, two time-domain operational modal analysis methods, the data-driven stochastic subspace identification (SSI-DATA) method and the covariance-driven stochastic subspace identification (SSI-COV) method, are employed to identify the modal parameters from field recorded ambient acceleration data. On the basis of the SSI-DATA method, the modal contribution indexes of all identified modes to the measured acceleration data are computed by using the Kalman filter, and their applicability to evaluate the robustness of identified modes is also investigated. Here, the benchmark problem, developed by Hong Kong Polytechnic University with field acceleration measurements under different excitation conditions of a cable-stayed bridge, is adopted to show the effectiveness of the proposed method. The results from the benchmark study show that the robustness of identified modes can be judged by using their modal contributions to the measured vibration data. A critical value of modal contribution index of 2% for a reliable identifiability of modal parameters is roughly suggested for the benchmark problem.

• 한국정보과학회논문지:데이타베이스
• /
• 제34권4호
• /
• pp.328-342
• /
• 2007

본 논문에서는 데이타의 갱신이 빈번한 상황에서 데이타의 갱신을 효율적으로 처리하기 위한 색인 기법을 제안한다. 제안하는 색인구조는 대표적인 공간 분할 색인 기법 중 하나인 KDB-트리를 기반으로 하고 있으며, 캐시의 활용도를 높이기 위한 데이타 압축 기법과 포인터 제거 기법을 제안한다. 제안하는 기법의 우수성을 보이기 위해서 기존의 대표적인 캐시를 고려한 색인 구조중 하나인 CR-트리와 실험을 통해 성능을 비교하였으며, 성능평가 결과, 제안하는 색인 구조는 삽입 성능과 갱신 성능, 캐시 활용도 면에서 기존 색인 기법에 비해 각각 85%, 97%, 86% 의 성능이 향상되었다.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2000년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2000
• /
• pp.239-244
• /
• 2000

The necessity of the seismic performance evaluation of existing building structures is raised through the Taiwan earthquake in 1999. In this study, the methods of seismic performance evaluation of existing building structures in U.S.A. and Japan were reviewed, applied them to the three-story office building structures in Seoul. It is found out that it is possible to establish the seismic performance evaluation index of RC structure which meet Korean seismic code. Also it is concluded that if sufficient experimental and analytical data could be obtained, a reliable index for the evaluation of seismic performance of existing structures should be established in Korea.

• International Journal of Contents
• /
• 제1권1호
• /
• pp.50-58
• /
• 2005

Generally, multidimensional data such as image and spatial data require large amount of storage space. There is a limit to store and manage those large amounts of data in single workstation. If we manage the data on parallel computing environment which is being actively researched these days, we can get highly improved performance. In this paper, we propose a parallel multidimensional index structure that exploits the parallelism of the parallel computing environment. The proposed index structure is nP(processor)-nxmD(disk) architecture which is the hybrid type of nP-nD and 1P-nD. Its node structure in-creases fan-out and reduces the height of an index. Also, a range search algorithm that maximizes I/O parallelism is devised, and it is applied to k-nearest neighbor queries. Through various experiments, it is shown that the proposed method outperforms other parallel index structures.