• 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.

• The KIPS Transactions:PartD
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• v.14D no.6
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• pp.605-614
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• 2007

As a standard query language to search XML data, XQuery and XPath were proposed by W3C. By widely using XQuery and XPath languages, recent researches focus on the development of query processing algorithm and data structure for efficiently processing XML query with the enormous XML database system. Recently, when processing XML path expressions, the concept of the structural join which may determine the structural relationship between XML elements, e.g., ancestor-descendant or parent-child, has been one of the dominant XPath processing mechanisms. However, structural joins which frequently occur in XPath query processing require high cost. In this paper, we propose a new structural join algorithm, called SISJ, based on our structured index, called SI, in order to process XPath queries efficiently. Experimental results show that our algorithm performs marginally better than previous ones. However, in the case of high recursive documents, it performed more than 30% by the pruning feature of the proposed method.

• Journal of KIISE:Databases
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• v.32 no.3
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• pp.334-343
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• 2005

Complex queries such as path alld twig patterns have been the focus of much research on processing XML data. Structural join algorithms use a form of encoded structural information for elements in an XML document to facilitate join processing. Recently, structural join algorithms such as Twigstack and TSGeneric- have been developed to process such complex queries, and they have been shown that the processing costs of the algorithms are linearly proportional to the sum of input data. However, the algorithms have a shortcoming that their processing costs increase with the length of a queery. To overcome the shortcoming, we propose the segment join technique to augment the structural join with structural indexes such as the 1-Index. The SegmentTwig algorithm based on the segment join technique performs joins between a pair of segments, which is a series of query nodes, rather than joins between a pair of query nodes. Consequently, the query can be processed by reading only a query node per segment. Our experimental study shorts that segment join algorithms outperform the structural join methods consistently and considerably for various data sets.

• Journal of KIISE:Databases
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• v.33 no.7
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• pp.754-765
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• 2006

In XML keyword search, a search result is defined as a set of the smallest elements (i.e., least common ancestors) containing all query keywords and a granularity of indexing is an XML element instead of a document. Under the conventional index structure, all least common ancestors produced by the combination of the elements, each of which contains a query keyword, are considered as a search result. In this paper, to avoid unnecessary operations of producing the least common ancestors and reduce query process time, we describe a way to construct a partitioned index composed of several partitions and produce a search result by merging those partitions if necessary. When a search result is restricted to be composed of the least common ancestors whose depths are higher than a given minimum depth, under the proposed partitioned index structure, search systems can reduce the query process time by considering only combinations of the elements belonging to the same partition. Even though the minimum depth is not given or unknown, search systems can obtain a search result with the partitioned index, which requires the same query process time to obtain the search result with non-partitioned index. Our experiment was conducted with the XML documents provided by the DBLP site and INEX2003, and the partitioned index could reduce a substantial amount of query processing time when the minimum depth is given.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10c
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• pp.220-222
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• 2002

XML 문서의 효율적인 저장 및 검색을 위한 많은 연구들이 수행되고 있다. 그러나 기존의 연구들에서는 주로 내용 검색의 정확도를 높이기 위해 구조적 정보를 이용하는 방법을 제시하고 있으나, 순수하게 구조만을 대상으로 하는 인덱싱 및 질의 처리 방법 특히 , 동적인 환경을 고려한 인덱싱 및 질의 처리 방법에 대해서는 많이 언급하고 있지 않다. 본 논문에서는 XML 문서에 대한 순수 구조 질의 처리가 가능하고, 엘리먼트의 삭제 및 삽입 등 동적인 변경을 처리할 수 있는 인덱스 구조를 설계한다. 또한 설계된 인덱스 구조를 기반으로 순수 질의 처리 유형을 분류하고 각각에 대한 질의 처리 방안을 제시한다.

• Journal of KIISE:Databases
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• v.31 no.6
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• pp.567-584
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• 2004

As XML becomes popular as the way of presenting information on the web, how to secure XML data becomes an important issue. So far study on XML security has focused on security of data communications by using digital sign or encryption technology. But, it now requires not just to communicate secure XML data on communication but also to manage query process to access XML data since XML data becomes more complicated and bigger. We can manage XML data queries by access control technique. Right now current XML data access control only deals with read operation. This approach has no option to process update XML queries. In this paper, we present XML access control model and technique that can support both read and update operations. In this paper, we will propose the operation for XML document update. Also, We will define action type as a new concept to manage authorization information and process update queries. It results in both minimizing access control steps and reducing memory cost. In addition, we can filter queries that have no access rights at the XML data, which it can reduce unnecessary tasks for processing unauthorized query. As a result of the performance evaluation, we show our access control model is proved to be better than other access control model in update query. But it has a little overhead to decide action type in select query.

• The KIPS Transactions:PartD
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• v.9D no.6
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• pp.999-1008
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• 2002

XML is emerging as a standard data format to exchange and to present data on the Web. There are increasing needs to efficiently store and to query XML data. In this paper. we propose a new schema transformation algorithm based on a common structure extracting technique from XML documents. The common structure is shared by all XML documents referenced by DTD and the uncommon structure is ununiformly appeared on all XML documents referenced by DTD. Based on the extracted common and uncommon structures, we transform XML DTD into relational database schema. We conduct a performance evaluation based on the number of the generated tables, the size of the record, query processing time and the number of joins on the query. The performance of our algorithm is compared with the existing algorithms, then in most cates, our algorithm is better than the existing ones with respect to the number of the generated tables and appearance of NULL values in the tables.

• Journal of the Korean Institute of Intelligent Systems
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• v.16 no.1
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• pp.94-100
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• 2006

Computing paradigm shift to internet-based one has accelerated the use of XML in diverse applications. This phenomena has made the explosive increases of XML data and it triggered many active researches in maintaining very huge amount of XML data in turn. In this paper we present a persistent graph-based XML indexing lot data-centric XML data. In our approach we use 3 graphs to represent XML indexes and XML data itself. They are schema graph, data graph index. And then we have mapped those graphs to B+-trees the persistency. With our approach we can achieve linear query execution time with the increase of XML sizes.

• Proceedings of the Korea Inteligent Information System Society Conference
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• 2002.05a
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• pp.230-238
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• 2002

기업간 전자거래의 급속한 발전은 선진 각국뿐만 아니라 국내에서도 국가적인 차원에서 전자거래 활성화 방안을 수립하여 진행하고 있다. 그러나, 기업-소비자간 거래(B2C)와는 다르게 기업간 전자거래(B2B)의 활성화를 위해서는 기업의 생산 능력 및 가격, 신뢰성에 근거한 고도의 구조화된 정보를 효율적으로 검색할 수 있는 방법이 요구된다. 이러한 고도의 구조화 된 정보에 기반 한 전자거래를 위해서 정부에서도 지난 2001년 8월 XML기반의 전자 거래를 위한 데이터 교환 모델인 ebXML을 권고안으로 선정한 바가 있다. XML을 활용하여 데이터의 구조에 의미를 부여하는 것은 기업에 달려 있지만, 결과적으로 구축한 데이터를 어떻게 효율적으로 검색하여, 자기 기업에 맞는 최적의 전자 거래 파트너를 찾을 것인가라는 문제는 기업간 전자거래(B2B)의 고도화, 활성화를 위한 필수적인 과제이다. 본 논문의 목표는 ebXML 프레임웍에서 효율적인 거래파트너 검색을 위한 XML 기반의 검색시스템을 개발하는 것이며, 이는 중소기업의 정보화 및 경쟁력 강화에 큰 역할을 할 수 있을 것이라 판단된다.

• Journal of Korea Multimedia Society
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• v.12 no.2
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• pp.178-190
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• 2009

XML is recommended by W3C(World Wide Web) and widely accepted as a standard markup language for expression and sharing data. Recently, increasing the use and the amount of XML documents, there is required that easy methods for accessing XML documents at anytime and anywhere, therefore, the distributed XML repository systems is developed. For this, distributed XML repository systems is necessary to research catalog management schemes. In this paper, we design distributed XML database model considering CPU costs, I/O costs, concurrency control, two-phase commits a protocol, queuing delay and so on. And we implement a simulator in order to execute performance evaluation centralized catalog method, fully replicated catalog method, and partitioned catalog method using reasonably setting up environments.