François Bry, Tim Furche, Benedikt Linse, Sebastian Schaffert, Andreas Schroeder:
Tim Furche (editor):
Declarative Semantics and Query Core for the Xcerpt Query Language.

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In: (I4-D8)

This article introduces a preliminary declarative semantics for a subset of the language Xcerpt (so-called grouping-stratifable programs) in form of a classical (Tarski style) model theory, adapted to the specic requirements of Xcerpt's constructs (e.g. the various aspects of incompleteness in query terms, grouping constructs in rule heads, etc.). Most importantly, the model theory uses term simulation as a replacement for term equality to handle incomplete term specifications, and an extended notion of substitutions in order to properly convey the semantics of grouping constructs. Based upon this model theory, a fixpoint semantics is also described, leading to a first notion of forward chaining evaluation of Xcerpt programs. In a second part of this deliverable, syntax, semantics, complexity, and evaluation for the query core of Xcerpt (and many other Web query languages such as XQuery and SPARQL) is introduced and discussed.



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