Disjunctive logic programming (DLP) is a very expressive formalism. It allows forexpressing every property of finite structures that is decidable in thecomplexity class ΣP2(=NPNP). Despite this high expressiveness, thereare some simple properties, often arising in real-world applications, whichcannot be encoded in a simple and natural manner. Especially properties thatrequire the use of arithmetic operators (like sum, times, or count) on a set ormultiset of elements, which satisfy some conditions, cannot be naturallyexpressed in classic DLP. To overcome this deficiency, we extend DLP byaggregate functions in a conservative way. In particular, we avoid theintroduction of constructs with disputed semantics, by requiring aggregates tobe stratified. We formally define the semantics of the extended language (called ), and illustrate how it can be profitably used for representingknowledge. Furthermore, we analyze the computational complexity of , showing that the addition of aggregates does not bring a highercost in that respect. Finally, we provide an implementation of in DLV—a state-of-the-art DLP system—andreport on experiments which confirm the usefulness of the proposed extensionalso for the efficiency of computation.

Tracers provide users with useful information about program executions. In thisarticle, we propose a “tracer driver”. From a single tracer,it provides a powerful front-end enabling multiple dynamic analysis tools to beeasily implemented, while limiting the overhead of the trace generation. Therelevant execution events are specified by flexible event patterns and a largevariety of trace data can be given either systematically or “ondemand”. The proposed tracer driver has been designed in the contextof constraint logic programming (CLP); experiments have been made withinGNU-Prolog. Execution views provided by existing tools have been easily emulatedwith a negligible overhead. Experimental measures show that the flexibility andpower of the described architecture lead to good performance. The tracer driveroverhead is inversely proportional to the average time between two tracedevents. Whereas the principles of the tracer driver are independent of thetraced programming language, it is best suited for high-level languages, such asCLP, where each traced execution event encompasses numerous low-level executionsteps. Furthermore, CLP is especially hard to debug. The current environments donot provide all the useful dynamic analysis tools. They can significantlybenefit from our tracer driver which enables dynamic analyses to be integratedat a very low cost.

Requirements about the quality of clinical guidelines can be represented byschemata borrowed from the theory of abductive diagnosis, using temporal logicto model the time-oriented aspects expressed in a guideline. Previously, we haveshown that these requirements can be verified using interactive theorem provingtechniques. In this paper, we investigate how this approach can be mapped to thefacilities of a resolution-based theorem prover, otter and acomplementary program that searches for finite models of first-order statements,mace-2. It is shown that the reasoning required for checking thequality of a guideline can be mapped to such a fully automated theorem-provingfacilities. The medical quality of an actual guideline concerning diabetesmellitus 2 is investigated in this way.

In everyday life it happens that a person has to reason out what other peoplethink and how they behave, in order to achieve his goals. In other words, anindividual may be required to adapt his behavior by reasoning about the others'mental state. In this paper we focus on a knowledge-representation languagederived from logic programming which both supports the representation of mentalstates of individual communities and provides each with the capability ofreasoning about others' mental states and acting accordingly. The proposedsemantics is shown to be translatable into stable model semantics of logicprograms with aggregates.

We introduce an extended tableau calculus for answer set programming (ASP). Theproof system is based on the ASP tableaux defined in the work by Gebser andSchaub (Tableau calculi for answer set programming. In Proceedings ofthe 22nd International Conference on Logic Programming (ICLP 2006),S. Etalle and M. Truszczynski, Eds. Lecture Notes in Computer Science, vol.4079. Springer, 11–25) with an added extension rule. We investigatethe power of Extended ASP Tableaux both theoretically and empirically. We studythe relationship of Extended ASP Tableaux with the Extended Resolution proofsystem defined by Tseitin for sets of clauses, and separate Extended ASPTableaux from ASP Tableaux by giving a polynomial-length proof for a family ofnormal logic programs {Φn} for which ASP Tableaux has exponential-length minimal proofs withrespect to n. Additionally, Extended ASP Tableaux implyinteresting insight into the effect of program simplification on the lengths ofproofs in ASP. Closely related to Extended ASP Tableaux, we empiricallyinvestigate the effect of redundant rules on the efficiency of ASP solving.

In this paper, a Gaifman–Shapiro-style module architecture is tailoredto the case of smodels programs under the stable model semantics. Thecomposition of smodels program modules is suitably limited by moduleconditions which ensure the compatibility of the module system with stablemodels. Hence the semantics of an entire smodels program dependsdirectly on stable models assigned to its modules. This result is formalized asa module theorem which truly strengthens V. Lifschitz and H.Turner's splitting-set theorem (June 1994, Splitting a logic program. InLogic Programming: Proceedings of the Eleventh InternationalConference on Logic Programming, Santa Margherita Ligure, Italy, P.V. Hentenryck, Ed. MIT Press, 23–37) for the class of smodelsprograms. To streamline generalizations in the future, the module theorem isfirst proved for normal programs and then extended to cover smodelsprograms using a translation from the latter class of programs to the formerclass. Moreover, the respective notion of module-level equivalence, namelymodular equivalence, is shown to be a proper congruencerelation: it is preserved under substitutions of modules that are modularlyequivalent. Principles for program decomposition are also addressed. Thestrongly connected components of the respective dependency graph can beexploited in order to extract a module structure when there is no explicita priori knowledge about the modules of a program. Thepaper includes a practical demonstration of tools that have been developed forautomated (de)composition of smodels programs.