Despite a large body of work on XPath query processing in relational environment, systematic study of queries containing not-predicates have received little attention in the literature. Particularly, several xml supports of industrial-strength commercial rdbms fail to efficiently evaluate such queries. In this paper, we present an efficient and novel strategy to evaluate not -twig queries in a tree-unaware relational environment. not -twig queries are XPath queries with ancestor–descendant and parent–child axis and contain one or more not-predicates. We propose a novel Dewey-based encoding scheme called Andes ( AN cestor D ewey-based E ncoding S cheme), which enables us to efficiently filter out elements satisfying a not-predicate by comparing their ancestor group identifiers . In this approach, a set of elements under the same common ancestor at a specific level in the xml tree is assigned same ancestor group identifier . Based on this scheme, we propose a novel sql translation algorithm for not -twig query evaluation. Experiments carried out confirm that our proposed approach built on top of an off-the-shelf commercial rdbms significantly outperforms state-of-the-art relational and native approaches. We also explore the query plans selected by a commercial relational optimizer to evaluate our translated queries in different input cardinality. Such exploration further validates the performance benefits of Andes .
The VLDB Journal – Springer Journals
Published: Dec 1, 2012
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