• The KIPS Transactions:PartD
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• v.13D no.1 s.104
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• pp.11-22
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• 2006

As we are to deal with more and more XML documents, research on storing and managing XML documents in databases are actively conducted. Employing RDBMS or ORDBMS as a repository of XML documents is currently regarded as most practical. The query results out of XML documents stored in databases could be cached for query performance though the cost of cache consistency against the update of the underlying data is incurred. In this paper, we assume that an ORDBMS is used as a repository for the XML query cache as well as its underlying XML documents, and that XML query cache is refreshed in a deferred way with the update log. When the same XML document was updated multiple times, the deferred refresh of the XML query cache may Bet inefficient. We propose an algorithm that removes or filters such duplicate updates. Based on that, the optimal SQL statements that are to be executed for XML query cache consistency are generated. Through experiments, we show the efficiency of our proposed deferred refresh of XML query cache.

• Journal of KIISE:Databases
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• v.33 no.5
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• pp.551-562
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• 2006

XML query caching for XML database-backed Web applications began to be investigated recently. Despite its practical significance, efficiency of the storage schemes for cached query results has not been addressed. In this paper, we deal with the storage schemes for XML query cache. A fundamental problem that needs to be considered in designing an efficient storage structure for XML query cache is that there exist performance tradeoffs between the two major types of operations on a cached query result. The two are (1) retrieving the whole of it to return the query result and (2) updating just a small portion of it for its incremental refresh against the updates done to its source. We propose eight different storage schemes for XML query cache, which are categorized into three groups: (1) the schemes based on the plain text file, (2) the schemes based on the persistent DOM (PDOM) file, and (3) a scheme employing an RDBMS. We implemented all of them, and compared their performance with each other. We also compared our proposal with a storage scheme based on a current state-of-the-art XML storage scheme, showing that ours is more efficient.

• The Journal of Society for e-Business Studies
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• v.12 no.3
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• pp.211-234
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• 2007

In e-business, XML is a major format of data and it is essential to efficiently process queries against XML data. XML query caching has received much attention for query performance improvement. In employing XML query caching, some efficient technique of cache replacement is required. The previous techniques considered as a replacement unit either the whole query result or the path in the query result. The former is simple to employ but it is not efficient whereas the latter is more efficient and yet the size difference among the potential victims is large, and thus, efficiency of caching would be limited. In this paper, we propose a new technique where the element in the query result is are placement unit to overcome the limitations of the previous techniques. The proposed technique could enhance the cache efficiency to a great extent because it would not pick a victim whose size is too large to store a new cached item, the variance in the size of victims would be small, and the unused space of the cache storage would be small. A technique of XML semantic cache replacement is presented which is based on the replacement function that takes into account cache hit ratio, last access time, fetch time, size of XML semantic region, size of element in XML semantic region, etc. We implemented a prototype XML semantic cache system that employs the proposed technique, and conducted a detailed set of experiments over a LAN environment. The experimental results showed that our proposed technique outperformed the previous ones.

• The KIPS Transactions:PartD
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• v.11D no.2
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• pp.293-304
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• 2004

Recently, caching for the database-backed web applications has received much attention. The results of frequent queries could be cached for repeated reuse or for efficient processing of the relevant queries. Since the emergence of XML as a standard for data exchange on the web, today's web applications are to retrieve information from the remote XML sources across the network, and thus it is desirable to maintain the XML query results in the cache for the web applications. In this paper, we describe implementation of an XML query processing system that supports cache-answerability of XML queries, and evaluate its performance. XML path expression, which is one of the core features of XML query languages including XQuery, XPath, and XQL was considered as the XML query. Their result is maintained as an XML materialized view in the XML cache. The algorithms to rewrite the given XML path expression using its relevant materialized view proposed in [13] were implemented with RDBMS as XML store. The major issues of implementation are described in detail. The results of performance experiments conducted with the implemented system showed effectiveness of cache-answerability of XML queries. Comparison with previous research in terms of performance is also Provided.

• The Journal of Society for e-Business Studies
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• v.11 no.1
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• pp.1-23
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• 2006

As data on the Web is more and more in XML due to proliferation of Web applications such as e-Commerce, it is strongly required to rapidly process XML queries. One of such techniques is XML query caching. For frequently submitted queries, their results could be cached in order to guarantee fast response for the same queries. In this paper, we propose techniques for XML query performance improvement whereby the set of node identifiers(NIS) for an XML query is cached. NIS is most commonly employed as a format of XML query result,, consisting of the identifiers of the XML elements that comprise the query result. With NIS, it is suitable to meet the Web applications data retrieval requirements because reconstruction and/or modification of query results and integration of multiple query results can be efficiently done. Incremental refresh of NIS against its source updates can also be efficiently done. When the query result is requested in XML, however, materialization of NIS is needed by retrieving the source XML elements through their identifiers. In this paper, we consider three different types of NISs. proposing the algorithms of their creation, materialization, and incremental refresh. All of them were implemented using an RDBMS. Through a detailed set of performance experiments, we showed the efficiency of the proposed XML query caching techniques.

• Journal of KIISE:Computing Practices and Letters
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• v.11 no.5
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• pp.393-400
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• 2005

XML makes it possible to query the information created and managed different applications, which is impossible if expressed in other structure or language. In using shipbuilding information management system, there is inefficiency in storing and querying such a large XML document in XDBox. XML proxy cache system is suggested to improve that. In this paper, we suggests XML proxy cache system with thought of update locality found in using shipbuilding information management system.

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

• Proceedings of the Korea Information Processing Society Conference
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• 2005.05a
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• pp.59-62
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• 2005

웹 상에서 XML 로 기술된 데이터가 증가하고, 이를 이용하여 의미 있는 데이터를 검색하는 것의 중요성이 커지고 있다. 웹 상에서 더 좋은 검색 성능을 보이기 위해 XML 질의 결과를 캐쉬하는 방법에 관한 연구들과 캐쉬의 저장 공간과 다양한 질의를 캐쉬에 저장하는 것에 한계가 있기 때문에 캐쉬 교체 기법에 관한 연구들이 있었다. 기존의 XML 캐쉬 교체 정책에는 질의 결과를 교체 단위로 하는 방법과 질의 결과 내의 각 경로들을 교체 단위로 하는 방법이 있는데, 첫번째 방법은 효율이 상대적으로 낮고 두번째 방법은 높은 효율에 비해 교체 연산을 수행하는 부담(overhead)이 크다는 단점이 있었다. 본 논문에서는 위 두 방법의 단점을 해결하기 위해 2 단계로 교체 희생자를 선택하는 방법을 제시한다. 질의 결과들 중에서 교체 희생자를 찾고, 그 희생자 내의 모든 경로들 중에서 다시 교체 희생자를 찾는다. 이는 각 질의 내의 경로가 교체 희생자가 되어 캐쉬 효율을 향상 시키고, 질의 결과에 대해 먼저 교체 대상을 찾으므로 교체 희생자를 찾기 위한 연산을 수행하는 부담을 줄인다. 또한 캐쉬 적중률, 최근 접근 시간, 인출 지연 시간, 객체 크기를 고려하여 교체 희생자를 선택하는 교체 함수를 제시한다. 가상의 시맨틱 데이터에 대한 캐쉬 교체 시스템을 구현하여 본 논문에서 제시한 교체 기법과 교체 함수를 평가한 결과를 기술한다.