Tim Furche, François Bry, Sebastian Schaffert:
Tim Furche (editor):
Xcerpt 2.0: Specification of the (Core) Language Syntax.

Complete Text [
.pdf, 4.93MB]
In: (I4-D12)

This article defines a revised syntax for the I4 query language, Xcerpt. Indeed, not only a single syntax, but rather three syntactical forms of Xcerpt are introduced: (1) the termsyntax, a non-standard syntax that allows the succinct formulation of queries and is intended mostly for human authors; (2) the XML syntax provides a fine granular language markup in XML, ideal for processing through XML-based tools and for automated query generation or reasoning about query programs; (3) the compact XML syntax is a hybrid syntax of (1) and (2). The concepts are introduced UML. In addition to the formal syntax specification, principles of the syntax design are discussed. Furthermore, for a number of advanced constructs the reasoning supporting the design choice, as well as alternative solutions are illustrated. An impression of how the introduced language constructs allow to write and understand complex queries is given by numerous examples interspersed among the construct specifications. We discuss several major revisions to Xcerpt’s syntax from Deliverable I4-D6 in a second part: identity, grouping, and functions. We conclude with a report on ongoing work about modules and extended RDF support for Xcerpt. In an appendix we provide an ANTLR grammar for most of the core language used in the currently under-development Xcerpt 2.0 prototype.



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