Tractable Combinations of Global Constraints

We study the complexity of constraint satisfaction problems involving global constraints, i.e., special-purpose constraints provided by a solver and represented implicitly by a parametrised algorithm. Such constraints are widely used; indeed, they are one of the key reasons for the success of constraint programming in solving real-world problems. Previous work has focused on the development of efficient propagators for individual constraints. In this paper, we identify a new tractable class of constraint problems involving global constraints of unbounded arity. To do so, we combine structural restrictions with the observation that some important types of global constraint do not distinguish between large classes of equivalent solutions.Comment: To appear in proceedings of CP'13, LNCS 8124. arXiv admin note: text overlap with arXiv:1307.179

Introducing LoCo, a Logic for Configuration Problems

In this paper we present the core of LoCo, a logic-based high-level representation language for expressing configuration problems. LoCo shall allow to model these problems in an intuitive and declarative way, the dynamic aspects of configuration notwithstanding. Our logic enforces that configurations contain only finitely many components and reasoning can be reduced to the task of model construction.Comment: In Proceedings LoCoCo 2011, arXiv:1108.609

Optimization Methods for the Partner Units Problem

Abstract. In this work we present the Partner Units Problem as a novel challenge for optimization methods. It captures a certain type of configuration problem that frequently occurs in industry. Unfortunately, it can be shown that in the most general case an optimization version of the problem is intractable. We present and evaluate encodings of the problem in the frameworks of answer set programming, propositional satisfiability testing, constraint solving, and integer programming. We also show how to adapt these encodings to a class of problem instances that we have recently shown to be tractable.

Wettbewerb und Regulierung jetzt auch in der Wasserwirtschaft

Die Verfügungen der Landeskartellbehörde Hessen gegen Wasserversorger wegen zu hoher Wasserpreise, die auf eine Vergleichsmarktanalyse gestützt wurden, und deren Bestätigung durch den BGH am 2.2.2010 waren erste Vorboten einer sich verschärfenden kartellrechtlichen Entgeltkontrolle der Wasserwirtschaft. Die folgende Entscheidung der Landeskartellbehörde Baden-Württemberg auf der Basis einer Kostenanalyse ein Jahr später ist dagegen unlängst vom OLG Stuttgart gestoppt worden. Vor dem Hintergrund der dadurch ausgelösten Unsicherheiten stellt sich die Frage, ob die Wasserwirtschaft nicht wie die anderen Netzwirtschaften (Telekommunikation, Energie, Post, Eisenbahntransport) auch einer Regulierung durch die in den übrigen Wirtschaftszweigen erfolgreich tätige Bundesnetzagentur unterworfen werden sollte. Der Beitrag gelangt zu dem Ergebnis, dass der kartellrechtliche Ansatz gegenwärtig sinnvoll ist und die Option auf eine abgabenrechtliche Kontrolle beseitigt werden muss. Sollte sich die kartellrechtliche Kontrolle jedoch nicht als wirksam herausstellen, so wäre eine bundeseinheitliche, sektorspezifische Lösung zu prüfen. Summary In the past, the Hessian Cartel Authority issued orders against water suppliers because they were charging excessively high prices and abused their dominant position. Those decisions were based on an analysis of comparable markets. These orders were upheld by the Federal Surpreme Court (BGH) on February 2, 2010. In this development one can see somewhat of a forerunner of a pricing regulation through antitrust law within the water industry. However, the following decision by the Cartel Authority of Baden-Wuerttemberg one year later, which was based on an analysis of the actual costs was only recently quashed by the Higher Regional Court (OLG) of Stuttgart. Considering the resulting insecurities regarding the application of the legal framework, the question arises, whether the water suppliers should be subjected to regulation by the Federal Network Authority – just like other network based industries, such as telecommunications, energy, post and railways. This paper comes to the conclusion that the current approach using the antitrust law is generally reasonable as a first step. What seems even more important than the choice between a sector specific regulation and antitrust law is to abolish the option of an administrative price control of public water suppliers which proved to be ineffective. Should the full application of cartel law, however, turn out to be ineffective in the future, a national sector specific solution should be considered. JEL Classification: K

Lifting Structural Tractability to CSP with Global Constraints

A wide range of problems can be modelled as constraint satisfaction problems (CSPs), that is, a set of constraints that must be satisfied simultaneously. Constraints can either be represented extensionally, by explicitly listing allowed combinations of values, or implicitly, by special-purpose algorithms provided by a solver. Such implicitly represented constraints, known as global constraints, are widely used; indeed, they are one of the key reasons for the success of constraint programming in solving real-world problems. In recent years, a variety of restrictions on the structure of CSP instances that yield tractable classes have been identified. However, many such restrictions fail to guarantee tractability for CSPs with global constraints. In this paper, we investigate the properties of extensionally represented constraints that these restrictions exploit to achieve tractability, and show that there are large classes of global constraints that also possess these properties. This allows us to lift these restrictions to the global case, and identify new tractable classes of CSPs with global constraints.Comment: To appear in proceedings of CP'13, LNCS 812