• Journal of the Korea Society of Computer and Information
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• v.15 no.11
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• pp.11-20
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• 2010

XML view is proposed to integrate between XML data and heterogeneous data over distributed environment and global XML view is used to search distributed heterogeneous data. At this time, standard query language for user is XQuery and the method for processing global XQuery queries over distributed environment is one of the new research topics. One of the basic and simple methods to process distributed SQL queries is that generates local queries for processing a global query and constructs the result of the global query from the results of the local queries. However, the syntax of XQuery differs from SQL because the XQuery contains some special expressions like FOR clauses for querying to semi-structured data, of course, FOR clauses are not used in SQL. Therefore, there are some problems to adopt the method for processing global SQL queries for generating local XQuery queries. This paper defines some problems when generates local XQuery queries for processing global XQuery queries and proposes a method for generating local XQuery queries considered these problems. Also we implement and evaluate a Global XQuery Processor which uses our method.

• Journal of KIISE:Databases
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• v.34 no.6
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• pp.564-571
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• 2007

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.