摘要
Finding all occurrences of a twig query in an XML database is a core operation for efficient evaluation of XML queries. It is important to effiectively handle twig queries with wildcards. In this paper, a novel path-partitioned encoding scheme is proposed for XML documents to capture paths of all elements, and a twig query is modeled as an XPattern extended from tree pattern. After definition, simplification, normalization, verification and initialization of the XPattern, both work sets and a join plan are generated. According to these measures, an effiective algorithm to answer for a twig query, called DMTwig, is designed without unnecessary elements and invalid structural joins. The algorithm can adaptively deal with twig queries with branch ([ ]), child edge (/), descendant edge (//), and wildcard (*) synthetically. We show that path-partitioned encoding scheme and XPattern guarantee the I/O and CPU optimality for twig queries. Experiments on representative data set indicate that the proposed solution performs significantly.
Finding all occurrences of a twig query in an XML database is a core operation for efficient evaluation of XML queries. It is important to effiectively handle twig queries with wildcards. In this paper, a novel path-partitioned encoding scheme is proposed for XML documents to capture paths of all elements, and a twig query is modeled as an XPattern extended from tree pattern. After definition, simplification, normalization, verification and initialization of the XPattern, both work sets and a join plan are generated. According to these measures, an effiective algorithm to answer for a twig query, called DMTwig, is designed without unnecessary elements and invalid structural joins. The algorithm can adaptively deal with twig queries with branch ([ ]), child edge (/), descendant edge (//), and wildcard (*) synthetically. We show that path-partitioned encoding scheme and XPattern guarantee the I/O and CPU optimality for twig queries. Experiments on representative data set indicate that the proposed solution performs significantly.
基金
supported by the National High-Tech Research and Development Plan of China (Grant No.2005AA4Z3030)
