Twig Pattern Matching with Positional Predicates in XML Queries

Twig pattern matching is core operation in XML query processing. Although holistic twig pattern matching algorithms have been studied intensively nowadays, little attention is paid on positional predicates defined on navigation axis. These algorithms cannot be used to implement XPath queries with positional predicates, since the query results fail to be selected from the pattern matching results. For implementation of XPath query with the positional predicates, this paper extends the traditional twig pattern to a new one called ExTwig to deal with both positional predicates and following sibling axis. The corresponding holistic twig pattern matching algorithm TwigPos is also proposed to process ExTwig query. Comparison experiments on large benchmarks show that our algorithm is efficient and practical.