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Estimating Join Selectivity of Global XQuery Queries in Distributed Environments  

Park, Jong-Hyun (충남대학교 컴퓨터)
Kang, Ji-Hoon (충남대학교 컴퓨터)
Publication Information
Journal of KIISE:Databases / v.34, no.6, 2007 , pp. 564-571 More about this Journal
Abstract
One of the methods for integrating XML data in distributed environments is using XML view. User can query toward distributed local XML views by using global XQuery queries in XQuery which is a standard query language for searching XML data. The global XQuery queries naturally contain join operations because of integrating and searching distributed heterogeneous data. Since join operations are generally expensive for processing a query, its processing technique is very important for efficient processing of global XQuery queries. Therefore there are some studies on the efficient processing of join operations and one of these studies is that selects minimum join cost by estimating a join selectivity. In case of SQL, there are already some researches for estimating a join selectivity and join cost of global SQL queries. However we can not apply their methods for estimating the selectivity of join operations in SQL queries into XQuery queries because of the structural difference between relational data and XML data. Therefore this paper proposes a method for estimating a selectivity of join operations in XQuery queries using the information of XML views. Our contribution is three threefold. First, we define the difference point for estimating join selectivity between SQL and XQuery. Second, we estimate join selectivity in XQuery queries by referring XML views. Third, we evaluate our estimating method.
Keywords
Global XQuery Processing; Estimating Join Selectivity;
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