Containment for XPath Fragments under DTD Constraints
نویسنده
چکیده
The containment and equivalence problems for various fragments of XPath have been studied by a number of authors. For some fragments , deciding containment (and even minimisation) has been shown to be in ptime, while for minor extensions containment has been shown to be conp-complete. When containment is with respect to trees satisfying a set of constraints (such as a schema or DTD), the problem seems to be more diicult. For example, containment under DTDs is conp-complete for an XPath fragment denoted XP f ]g for which containment is in ptime. It is also undecidable for a larger class of XPath queries when the constraints are so-called simple XPath integrity constraints (SXICs). In this paper, we show that containment is decidable for an important fragment of XPath, denoted XP f ];;==g , when the constraints are DTDs. We also identify XPath fragments for which containment under DTDs can be decided in ptime.
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