This work studies relational joins from a theoretical perspective and shows that there exist queries for which the join-project plan suggested by the fractional edge cover approach may be substantially better than any join plan that does not use intermediate projections.Expand

This work provides a characterization of the resolution width introduced in the context of propositional proof complexity in terms of the existential pebble game and a surprising proof that the minimum space of refuting a 3-CNF formula is always bounded from below by the minimum width of refuted it.Expand

This work proves that a system is weakly automatizable exactly when a weak form of the satisfiability problem is solvable in polynomial time, and shows that Resolution proofs of its own consistency require almost exponential size.Expand

It is proved that, although the solver is not explicitly designed for it, with high probability it ends up behaving as width-k resolution after no more than O(n2k+2) conflicts and restarts, where n is the number of variables.Expand

This work proves the exact converse to this: if the core of the structure encoding the scopes of the constraints does not have treewidth at most k, then the k-consistency algorithm is not always correct.Expand

This work provides a characterization of the resolution width introduced in the context of propositional proof complexity in terms of the existential pebble game and a surprising proof that the minimum space of refuting a 3-CNF formula is always bounded from below by the minimum width of refuted it.Expand

It is shown that testing the solvability of systems of equations over a finite Abelian group, a tractable CSP that was previously known not to be definable in Datalog, is not Definable in an infinitary logic with counting and hence that it is not definite in least fixed point logic or its extension with counting.Expand

It is NP-hard to distinguish between formulas that have Resolution refutations of polynomial length and those that do not have subexponential length refutations.Expand

It is shown that refutations by ODBBs polynomially simulate resolution and can be exponentially stronger, and introduces new proof systems, based on representation classes, that have not been considered up to this point.Expand

It is shown that the preservation property holds for classes of acyclic structures, structures of bounded degree, and more generally structures that are wide in a sense that the authors will make precise, and that the property fails for the class of planar graphs.Expand