Logics for n-ary queries in trees.
In computer science many data are
shaped as trees. In the context of the Web, it is the case
for XML formatted data in particular. XML is a markup language
that has rapidly become a standard for information storage and
As query languages for relational databases are not well-suited to XML data, the need to have query languages specific to XML documents has increased. We distinguish unary queries which select a set of subparts of a document from n-ary queries which select a set of n-tuples of subparts of a document. Many logical formalisms for unary queries have been proposed, but less work has been done on logical formalisms for n-ary queries.
This thesis is a fundamental study of n-ary queries that proposes two logical formalisms for n-ary queries: an extension of the navigational paradigm of the W3C standard XPath to n-ary queries, called the composition language, and an adapation of the spatial logic TQL introduced by Cardelli and Ghelli.
The question of expressive power, the complexity of the query evaluation problem as well as the satisfiability problem are considered. In particular, the satisfiability problem for a TQL fragment is proved to be decidable by reduction to the emptiness test of a new class of tree automata with global constraints that is studied independently.