1 citations · 2 across the 4 of their papers we have counts for
4 papers
Comparing Downward Fragments of the Relational Calculus with Transitive Closure on Trees
Jelle Hellings, Marc Gyssens, Yuqing Wu +4
Motivated by the continuing interest in the tree data model, we study the expressive power of downward navigational query languages on trees and chains. Basic navigational queries…
Structural characterizations of the navigational expressiveness of relation algebras on a tree
George H. L. Fletcher, Marc Gyssens, Jan Paredaens +2
Given a document D in the form of an unordered node-labeled tree, we study the expressiveness on D of various basic fragments of XPath, the core navigational language on XML docume…
On the Conditional Independence Implication Problem: A Lattice-Theoretic Approach
Mathias Niepert, Dirk Van Gucht, Marc Gyssens
A lattice-theoretic framework is introduced that permits the study of the conditional independence (CI) implication problem relative to the class of discrete probability measures.…
Well-Definedness and Semantic Type-Checking in the Nested Relational Calculus and XQuery
Jan Van den Bussche, Dirk Van Gucht, Stijn Vansummeren
Two natural decision problems regarding the XML query language XQuery are well-definedness and semantic type-checking. We study these problems in the setting of a relational fragme…