Kappa-Join: Efficient Execution of Existential Quantification in XML Query Languages

Abstract

XML query languages feature powerful primitives for formulating queries involving comparison expressions which are existentially quantified. If such comparisons involve several scopes, they are correlated, and become difficult to evaluate efficiently. In this paper, we develop a new ternary operator, called Kappa-Join, for efficiently evaluating queries with existential quantification. In XML queries, a correlation predicate can occur conjunctively and disjunctively. Our decorrelation approach not only improves performance in the conjunctive case, but also allows decorrelation of the disjunctive case. The latter is not possible with any known technique. In an experimental evaluation, we compare the query execution times of the Kappa-Join with existing XPath evaluation techniques to demonstrate the effectiveness of our new operator.

Indexing and Querying the Compressed XML Data (IQCX)

“…This query can also be thought of as a correlation predicate query, because it compares a local context and an enclosing context. Correlation predicate queries in [5] are referred. Oracle takes time to execute nested queries because for each and every row in the outer table, it fetches each and every row in the inner table.…”

“…Oracle takes time to execute nested queries because for each and every row in the outer table, it fetches each and every row in the inner table. Thus in order to reduce the execution time, a new approach [5] is proposed in which the inner query is executed first and then the outer query is executed with the result of the inner query.…”

Efficiently Querying the Indexed Compressed XML Data (IQX)

“…IQCX proves to be efficient than XSAQCT and TREECHOP techniques. A new ternary operator is developed, called Kappa-Join [7], for efficiently evaluating queries with existential quantification. A correlation predicate which can occur conjunctively and disjunctively in XML queries are decorrelated efficiently in this work.…”

“…This query can also be thought of as a correlation predicate query, because it compares a local context and an enclosing context. Correlation predicate queries in [7] are referred. Oracle takes time to execute nested queries because for each and every row in the outer table, it fetches each and every row in the inner table.…”

“…Oracle takes time to execute nested queries because for each and every row in the outer table, it fetches each and every row in the inner table. Thus in order to reduce the execution time, a new approach [7] is proposed in which the inner query is executed first and then the outer query is executed with the result of the inner query.…”