Characterizing XML Twig Queries with Examples

Slawek Staworko, Piotr Wieczorek

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Typically, a (Boolean) query is a finite formula that defines a possibly infinite set of database instances that satisfy it (positive examples), and implicitly, the set of instances that do not satisfy the query (negative examples). We investigate the following natural question: for a given class of queries, is it possible to characterize every query with a finite set of positive and negative examples that no other query is consistent with. We study this question for twig queries and XML databases. We show that while twig queries are characterizable, they generally require exponential sets of examples. Consequently, we focus on a practical subclass of anchored twig queries and show that not only are they characterizable but also with polynomially-sized sets of examples. This result is obtained with the use of generalization operations on twig queries, whose application to an anchored twig query yields a properly contained and minimally different query. Our results illustrate further interesting and strong connections between the structure and the semantics of anchored twig queries that the class of arbitrary twig queries does not enjoy. Finally, we show that the class of unions of twig queries is not characterizable.
Original languageEnglish
Title of host publication18th International Conference on Database Theory, ICDT 2015, March 23-27, 2015, Brussels, Belgium
Number of pages17
Publication statusPublished - 19 Mar 2015


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