Keywords: Answer Set Programming, HEX-Programs, Modular Logic Programming

Answer Set Programming is a well-established paradigm of declarative programming in close relationship with other declarative formalisms such as SAT Modulo Theories, Constraint Handling Rules, PDDL and many others. Since its first informal editions, ASP systems are compared in the nowadays customary ASP Competition. The fourth ASP Competition, held in 2012/2013, is the sequel to previous editions and it was jointly organized by University of Calabria (Italy) and the Vienna University of Technology (Austria). Participants competed on a selected collection of benchmark problems, taken from a variety of research areas and real world applications. The Competition featured two tracks: the Model& Solve Track, held on an open problem encoding, on an open language basis, and open to any kind of system based on a declarative specification paradigm; and the System Track, held on the basis of fixed, public problem encodings, written in a standard ASP language.

Keywords: Benchmark, Competition

System competitions evaluate solvers and compare state-of-the-art implementations on benchmark sets in a dedicated and controlled computing environment comprising of multiple hosts. An important task for running a competition is the benchmark execution platform that schedules the workload on available benchmark machines, keeps track of failed and finished jobs, and calculates the competition statistics and solver ranking. In this paper we present VCWC, the Versioning Competition Workflow Compiler. This tool takes as input the participating solvers and dedicated benchmark sets and generates a workflow description for executing all necessary (sub-)tasks for generating the final solver rankings and statistics. As jobs may fail during the execution, VCWC supports a gradual refinement of the competition workflow and allows to add or update solvers, instances, benchmarks, or further runs after the machinery has been brought up. We introduce an abstract model for a competition and present the implementation and system architecture for VCWC. Based on this we report how VCWC is used for the Answer Set Programming Competition 2013.

Keywords: Benchmark, Competition

Answer set programs with external source access may introduce new constants that are not present in the program, which is known as value invention. As naive value invention leads to programs with infinite grounding and answer sets, syntactic safety criteria are imposed on programs. However, traditional criteria are in many cases unnecessarily strong and limit expressiveness. We present liberal domain-expansion (de-) safe programs, a novel generic class of answer set programs with external source access that has a finite grounding and allows for value invention. De-safe programs use so-called term bounding functions as a parameter for modular instantiation with concrete---e.g., syntactic or semantic or both---safety criteria. This ensures extensibility of the approach in the future. We provide concrete instances of the framework and develop an operator that can be used for computing a finite grounding. Finally, we discuss related notions of safety from the literature, and show that our approach is strictly more expressive.

Keywords: Answer Set Programming, External source access, Value invention, Safety criteria, Finite grounding