• The Journal of Society for e-Business Studies
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• v.11 no.4
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• pp.33-48
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• 2006

Since the emergence of XML as the standard for data exchange on the Web, XML warehousing technology is required to efficiently support Web business applications such as e-Commerce. When the RDBMS is employed as the storage for XML warehouse, XML materialized views of the XML warehouse could be provided by leveraging the materialized views of the RDBMS Because XML documents are mapped into relational tuples, an XML query defining an XML materialized view needs to be transformed into SQL. If relational materialized views were defined with the transformed SQL statements, the XML materialized view could be obtained just by XML-tagging the tuples of the corresponding relational materialized views. The foremost advantage of such a scheme is that the RDBMS does take care of XML materialized view consistency except XML tagging whenever their source XML documents are updated. In this paper, we proposed such a scheme of providing XML materialized views, and implemented it using a commercial RDBMS equipped with materialized view facility in Java on Windows 2000 Professional environment. XML documents in TPC-W, Web e-Commerce Benchmark, were used in performance experiments. The experimental results showed that our proposed scheme for XML materialized views was very effective.

• The KIPS Transactions:PartD
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• v.8D no.4
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• pp.327-338
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• 2001

The view can provide the user an appropriate portion of the database through data integration and filtering. Views can be materialized for query performance improvement, and in that cse, their consistency needs to be maintained against the updates of the underlying data. They can be either recomputed or incrementally refreshed by reflecting the relevant updates. Since XML could represent the structural information of the documents, for the XML materialized views, new techniques that differ from the previous ones for incrementally refreshing the relational views are required. In this paper, we propose a framework of XML materialized view management where the XML view derived from the underlying XML documents are materialized and incrementally refreshed against the updates of the underlying documents.

• The KIPS Transactions:PartD
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• v.10D no.3
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• pp.387-398
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• 2003

Materialized views have received much attention for query performance improvement. They need to be refreshed whenever their underlying data sources are updated. They could be recomputed from scratch or they could be incrementally refreshed by reflecting only those portions of updates that affect them. With emergence of XML as the standard for data exchange on the Web, active research is under way on effectively storing and retrieving XML documents. In this paper, we describe a performance study on the incremental refresh of XML materialized views for the case where XML documents are stored in a relational DBMS, and XML materialized views are maintained with incremental refresh. We describe implementation of a prototype XML storage system that supports XML materialized views and their incremental refresh, and report the performance results obtained with the implemented system through a detailed set of experiments on the incremental refresh of XML materialized views. The results show that the XML view maintenance with incremental refresh outperforms the ordinary view recomputation.

• The KIPS Transactions:PartD
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• v.10D no.4
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• pp.621-638
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• 2003

As demand of XML documents in the Web increases, Web service applications that manage XML documents as their resource are increasing. The view mechanism for XML data could be considered for effective in query processing in these Web service applications. If the XML query results are maintained as XML materialized views and their relevant XML query is processed using them, the query response time could be reduced. There are two types of processing an in path expression, which is one of the core features of XML query languages, using XML materialized views. One is the type where the complete query result is obtained from the materialized view, and the other is the type where some of the result is obtained from the materialized view and the rest is from the underlying XML documents. In this paper, we investigate the second type. An XML query in this paper is an XML path expression which is one of the core features of XML query languages. We first describe the storage structures of the XML materialized views derived from the underlying XML documents in the XML repository. Then, we propose the algorithms to decompose a given XML query into the subquery against the materialized view and the subquery against the underlying XML documents, and to integrate the results of these subqueries. Through performance evaluation, we figure out the condition under which our XML query decomposition using materialized views is more effective than the conventional processing.

• The KIPS Transactions:PartD
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• v.8D no.5
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• pp.461-472
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• 2001

Recently, much research on XML query processing considering the structural characteristics of XML documents is conducted, focusing primarily on the development and/or extension of XML query languages and on query optimization for effective retrieval of XML documents. In the XML repository, the XML views derived from the underlying XML documents could be stored materialized for effective retrieval of XML documents, and could be capitalized on for XML query processing In this paper, assuming that the XML views defined in XQL are materialized in the repository, we investigate XQL query processing that capitalizes on them. We describe the storage structure of the XML repository which supports the materialized views, and propose an algorithm that determines whether the given XQL query can be processed with the relevant materialized view adn accordingly transforms the original query into one against it.

• Proceedings of the Korean Information Science Society Conference
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• 2000.10a
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• pp.243-245
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• 2000

W3C(World Wide Web Consortium)가 XML(eXtensible Markup Language)을 차세대 웹 문서 표준으로 제안하면서 많은 응용에서 XML을 사용하려는 다양한 연구가 진행되고 있다. 뷰는 이질적인(heterogeneous) 데이터의 통합 및 여과(filtering) 기능을 통해서 사용자가 요구하는 데이터를 제공한다. 뷰의 구현 기법 중에서 실체 뷰(materialized view)는 뷰의 내용을 직접 저장하는 기법으로서, 사용자의 질의에 빠른 응답시간을 제공할 수 있다. 그러나 실체 뷰는 하부 데이터베이스가 변경되었을 경우에 일관성을 유지해야 하는 오버헤드가 있다. XML은 문서의 구조정보를 나타낼 수 있으므로 기존의 관계 데이터베이스와 객체지향 데이터베이스 등에서 연구되었던 실체 뷰 관리 기법과는 다른 XML 실체 뷰 관리 기법이 요구된다. 본 논문에서는 XML 문서를 대상으로 XML 실체 뷰를 지원하고, 데이터베이스에 저장된 XML 문서가 수정되었을 경우에 XML 실체 뷰에 대해 점진적 갱신(incremental refresh)을 지원하는 XML 실체 뷰 관리 프레임워크(framework)를 제안하였다.

• 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.

• 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.

• Journal of KIISE:Databases
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• v.30 no.3
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• pp.252-272
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• 2003

The view mechanism provides users with appropriate portions of database through data filtering and integration. In the Web era where information proliferates, the view concept is also useful for XML, a future standard for data exchange on the Web. This paper proposes a method of implementing XML views called XML view indexing, whereby XML view xv is represented as an XML view index(XVI) which is 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 but not the elements themselves, when a user requests to retrieve xv, its XVI should be materialized against xv's underlying XML documents. Also an efficient algorithm to incrementally maintain consistency of XVI given a update of xv's underlying XML documents is required. This paper proposes and implements data structures and algorithms for XML view indexing. The performance experiments on XML view indexing reveal that it outperforms view recomputation for repeated accesses to the view, and requires as much as about 30 times less storage space compared to XML view materialization though the latter takes less time for repeated accesses to the view due to no need of materialization.

• Journal of Internet Computing and Services
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• v.10 no.2
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• pp.99-116
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• 2009

For the mapping of two dimensional table structures of relational databases to the hierarchical XML documents, we apply the foreign key relationships of relational databases. In other words, the primary key of another table referenced by a foreign key of one tuple is mapped to the parent of the foreign key. Then XML hierarchies with order are expressed. In addition, the XML view file generated by the foreign key mappings shows side effects in the case of the relational database update for the satisfaction of referential integrity constraint in the foreign key. Thus, by inferring the foreign key roles at the generation of XML hierarchies, we can anticipate where the side effects occur in the hierarchies. We keep the XML view files up-to-date by reflecting the side effects to the XML files at the update of the underlying relational databases.