7 papers
Homomorphism Indistinguishability Beyond Graphs: Relational Weisfeiler--Leman and Hypertree Width
Panagiotis Aivasiliotis, Andreas Göbel, Matthias Lanzinger +1
The Weisfeiler--Leman (WL) algorithm is one of the most influential heuristics for the graph isomorphism problem. The expressive power of WL has been extensively studied in the con…
Cuts and Gauges for Submodular Width
Matthias Lanzinger
Submodular width is a central structural measure governing the complexity of conjunctive query evaluation. In this paper we recast submodular width in geometric terms. We how that…
FPT Parameterisations of Fractional and Generalised Hypertree Width
Matthias Lanzinger, Igor Razgon, Daniel Unterberger
We present the first fixed-parameter tractable (FPT) algorithms for exact computation of generalized hypertree width (ghw) and fractional hypertree width (fhw). Our algorithms are…
From Alternation to FPRAS: Toward a Complexity Classification of Approximate Counting
Markus Hecher, Matthias Lanzinger
Counting problems are fundamental across mathematics and computer science. Among the most subtle are those whose associated decision problem is solvable in polynomial time, yet who…
Selective Use of Yannakakis' Algorithm to Improve Query Performance: Machine Learning to the Rescue
Daniela Böhm, Georg Gottlob, Matthias Lanzinger +4
Query optimization has played a central role in database research for decades. However, more often than not, the proposed optimization techniques lead to a performance improvement…
Soft and Constrained Hypertree Width
Matthias Lanzinger, Cem Okulmus, Reinhard Pichler +2
Hypertree decompositions provide a way to evaluate Conjunctive Queries (CQs) in polynomial time, where the exponent of this polynomial is determined by the width of the decompositi…