Extending the Tractability Results on XPath Satisfiability with Sibling Axes
This paper extends the tractability results on XPath satisfiability with sibling axes under DC-DTDs, which were presented by the authors at DBPL 2009, in the following two directions. First, we provide a condition to extend a class of DTDs without spoiling the tractability of XPath satisfiability, provided that only child, descendant-or-self, parent, ancestor-or-self, following-sibling, and preceding-sibling axes, path union, and qualifier are taken into account. By applying the condition to DC-DTDs, we obtain a strictly broader but still tractable class of DTDs, where operators ? (zero or one occurrence) and + (one or more occurrences) are allowed in regular expressions in a restricted manner. Second, we extend the existing method of analyzing the satisfiability under DC-DTDs to a broader class of XPath expressions. Then, we show that the extended satisfiability analysis can be performed efficiently for a new subclass of XPath expressions.
KeywordsRegular Expression Tractable Class Content Model Candidate Node Schema Graph
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