Database Programming Languages

Volume 5708 of the series Lecture Notes in Computer Science pp 68-83

A Tractable Subclass of DTDs for XPath Satisfiability with Sibling Axes

  • Yasunori IshiharaAffiliated withOsaka University
  • , Takuji MorimotoAffiliated withOsaka University
  • , Shougo ShimizuAffiliated withAdvanced Institute of Industrial Technology
  • , Kenji HashimotoAffiliated withNara Institute of Science and Technology
  • , Toru FujiwaraAffiliated withOsaka University

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The paper presents a tractable subclass of DTDs, called DC-DTDs, for XPath satisfiability with sibling axes. A DC-DTD is a DTD such that each content model is in the form of a concatenation of single tag names and Kleene-starred regular expressions. DC-DTDs are a proper subclass of covering DTDs proposed by Montazerian et al., and a proper superclass of disjunction-free DTDs. In this paper, it is shown that tractability by covering DTDs is fragile against sibling axes. Then, tractability of XPath satisfiability with sibling axes under DC-DTDs is demonstrated. Finally, as a limitation of the tractability of DC-DTDs, it is shown that upward axes appearing in qualifiers bring intractability under even disjunction-free DTDs.