Querying XML with locator semantics
German National Research Center for Information Technology
Integrated Publication and Information Systems Institute
Dolivostraße 15, D-64293 Darmstadt, Germany
The prevailing data model for semi-structured data is XML. XQL is a
query language for XML that supports flexible navigation and filtering
on possibly irregular document trees by means of simple path expressions.
I present an approach to extend XQL with support for joins and for more
expressive extraction. To this end, locators are introduced, which allow
to identify document nodes by paths.
On this basis, a locator algebra (or L'Algebra for short) can be defined,
which supports matching, combination, and restructuring of XML documents
without excessive generation of new nodes. L'Algebra preserves document
order, and - by virtue of the locator semantics - also preservers regular
or irregular structure and navigation history.
I define the semantics of the main operators of L'Algebra, introduce its
axioms, and describe a mapping from XQL expressions to L'Algebra.
Peter Fankhauser has studied computer science at the Technical University
of Vienna. His PHD was on knowledge based methods for the integration of
heterogeneous database schemas. Since 1989 he is affiliated with the
Institute for Integrated Publication and Information Systems of
the GMD (German National Research Center for Information Technology)
in Darmstadt, Germany. He currently works on interoperability of