Hans Tompits

TU Wien | TU Wien · Institute of Information Systems

A significant challenge in the domain of autonomous vehicles is to ensure a reliable and safe operation in a multitude of contexts. As a consequence, autonomous vehicles must be capable of handling various context changes, such as changing weather conditions as well as software and hardware faults, without human support. To address this issue, we i...

This article deals with advanced notions of equivalence between nonmonotonic logic programs under the answer-set semantics, a topic of considerable interest, because such notions form the basis for program verification and are useful for program optimisation, debugging, and modular programming. In fact, there is extensive research in answer-set pro...

Paraconsistent logics constitute an important class of formalisms dealing with non-trivial reasoning from inconsistent premisses. In this paper, we introduce uniform axiomatisations for a family of nonmonotonic paraconsistent logics based on minimal inconsistency in terms of sequent-type proof systems. The latter are prominent and widely-used forms...

In this paper, we present the tool \(\mathsf {Uhura}\) for developing answer-set programs by means of specifying problem descriptions in a controlled natural language which then are translated into answer-set programming (ASP) rules. The tool is aimed for supporting users not familiar with answer-set programming—or logic-based approaches in general...

Starting with the seminal work on strong equivalence by Lifschitz, Pearce, and Valverde, many different advanced notions of program equivalence have been studied in the area of answer-set programming (ASP). In particular, relativised strong equivalence with projection has been introduced as a generalisation of strong equivalence by parameterising,...

In recent years, several approaches for formalising dishonest agents have been proposed in the artificial-intelligence literature. In particular, many of these approaches are based on a modal-logic setting. A prominent specimen of such a formalism is the multi-modal logic \(\mathsf {BIC}\), proposed by Sakama, Caminada, and Herzig, where the name “...

In recent years, different methods for supporting the development of answer-set programming (ASP) code have been introduced. During such a development process, often it would be desirable to have a natural-language representation of answer sets, e.g., when dealing with domain experts unfamiliar with ASP. In this paper, we address this point and pro...

Clause-elimination techniques that simplify formulas by removing redundant clauses play an important role in modern SAT solving. Among the types of redundant clauses, blocked clauses are particularly popular. For checking whether a clause C is blocked in a formula F, one only needs to consider the so-called resolution neighborhood of C, i.e., the s...

We present \(\mathsf {Harvey}\), a tool for random testing in answer-set programming (ASP) that allows to incorporate constraints to guide the generation of test inputs. Due to the declarative nature of ASP, it can be argued that there is less need for testing than in conventional software development. However, it is shown in practice that testing...

We introduce a stepping methodology for answer-set programming (ASP) that allows for debugging answer-set programs and is based on the stepwise application of rules. Similar to debugging in imperative languages, where the behaviour of a program is observed during a step-by-step execution, stepping for ASP allows for observing the effects that rule...

We introduce a stepping methodology for answer-set programming (ASP) that allows for debugging answer-set programs and is based on the stepwise application of rules. Similar to debugging in imperative languages, where the behaviour of a program is observed during a step-by-step execution, stepping for ASP allows for observing the effects that rule...

Clause-elimination procedures that simplify formulas in conjunctive normal form play an important role in modern SAT solving. Before or during the actual solving process, such procedures identify and remove clauses that are irrelevant to the solving result. These simplifications usually rely on so-called redundancy properties that characterize case...

Clause-elimination procedures that simplify formulas in conjunctive normal form play an important role in modern SAT solving. Before or during the actual solving process, such procedures identify and remove clauses that are irrelevant to the solving result. These simplifications usually rely on so-called redundancy properties that characterize case...

Blocked clauses provide the basis for powerful reasoning techniques used in SAT, QBF, and DQBF solving. Their definition, which relies on a simple syntactic criterion, guarantees that they are both redundant and easy to find. In this paper, we lift the notion of blocked clauses to first-order logic. We introduce two types of blocked clauses, one fo...

In theory and practice of modern SAT solving, clause-elimination procedures are essential for simplifying formulas in conjunctive normal form (CNF). Such procedures identify redundant clauses and faithfully remove them, either before solving in a preprocessing phase or during solving, resulting in a considerable speed up of the SAT solver. A wide n...

We consider a many-sorted variant of Japaridze's polymodal provability logic (GLP). In this variant, which is denoted GLP*, propositional variables are assigned sorts α ≤ ω, where variables of finite sort n < ω are interpreted as Pn+1-sentences of the arithmetical hierarchy, while those of sort ω range over arbitrary ones. We prove that GLP* is ari...

We consider a many-sorted variant of Japaridze's polymodal provability logic $\mathsf{GLP}$. In this variant, which is denoted $\mathsf{GLP}^\ast$, propositional variables are assigned sorts $\alpha \leq \omega$, where variables of finite sort $n < \omega$ are interpreted as $\Pi_{n+1}$-sentences of the arithmetical hierarchy, while those of sort $...

Traditional proof calculi are mainly studied for formalising the notion of valid inference, i.e., they axiomatise the valid sentences of a logic. In contrast, the notion of invalid inference received less attention. Logical calculi which axiomatise invalid sentences are commonly referred to as complementary calculi or rejection systems. Such calcul...

In this paper, we present SeaLion, an integrated development environment (IDE) for answer-set programming (ASP). SeaLion provides source-code editors for the languages of Gringo and DLV and offers popular amenities like syntax highlighting, syntax checking, code completion, visual program outline, and refactoring functionality. The tool has been re...

We address the problem of belief change in (nonmonotonic) logic programming under answer set semantics. Our formal techniques are analogous to those of distance-based belief revision in propositional logic. In particular, we build upon the model theory of logic programs furnished by SE interpretations, where an SE interpretation is a model of a log...

As is well known, answer-set programs do not satisfy the replacement property in general, i.e., programs and that are equivalent may cease to be so when they are put in the context of some other program , i.e., and may have different (sets of) answer sets. Lifschitz, Pearce, and Valverde (200126. Lifschitz , V , Pearce , D and Valverde , A . 200...

The employment of optimistic model versioning systems allows multiple developers of a team to work independently on their local copies of a software model. The merging process towards one consolidated version can be error-prone and time-consuming when performed without any tool support. Recently, several sophisticated approaches for model merging h...

This book constitutes revised selected papers of the 19th International Conference on Applications of Declarative Programming and Knowledge Management, INAP 2011, and the 25th Workshop on Logic Programming, WLP 2011, held in Vienna, Austria, in September 2011. The 19 papers presented in this volume were carefully reviewed and selected from 27 paper...

While past research in answer-set programming (ASP) mainly focused on theory, ASP solver technology, and applications, the present work situates itself in the context of a quite recent research trend: development support for ASP. In particular, we propose to augment answer-set programs with additional meta-information formulated in a dedicated anno...

In model-driven engineering, models are not primarily developed for documentation and requirement specification purposes, but promoted to first-class artifacts, from which executable code is generated. As a consequence, typical development activities like testing must be performed on the model level. In this paper, we propose to use overlapping inf...

Description-logic programs (or DL-programs for short) combine logic programs under the answer-set semantics with description logics for semantic-web reasoning. In order for a wider acceptance of the formalism among semantic-web engineers, it is vital to have adequate tools supporting the program development process. In particular, methods for debug...

We introduce an answer-set semantics for abstract-constraint programs with disjunction in rule heads in the style of Faber, Leone, and Pfeifer (FLP). To this end, we extend the definition of an answer set for logic programs with aggregates in rule bodies using the usual FLP-reduct. Additionally, we also provide a characterisation of our semantics i...

In software testing, the small-scope hypothesis states that a high proportion of errors can be found by testing a program for all test inputs within some small scope. In this paper, we evaluate the small-scope hypothesis for answer-set programming (ASP). To this end, we follow work in traditional testing and base our evaluation on mutation analysis...

Many applications require complexly structured data objects. Developing new or adapting existing algorithmic solutions for creating such objects can be a non-trivial and costly task if the considered objects are subject to different application-specific constraints. Often, however, it is comparatively easy to declaratively describe the required obj...

Current optimistic model versioning systems, which are indispensable to coordinate the collaboration within teams, are able to detect several kinds of conflicts between two concurrently modified versions of one model. These systems support the detection of syntactical problems such as contradicting changes, violations of the underlying metamodel, a...

We report about the current state and designated features of the tool SeaLion, aimed to serve as an integrated development environment (IDE) for answer-set programming (ASP). A main goal of SeaLion is to provide a user-friendly environment for supporting a developer to write, evaluate, debug, and test answer-set programs. To this end, new support t...

In answer-set programming (ASP), the solutions of a problem are encoded in dedicated models, called answer sets, of a logical theory. These answer sets are computed from the program that represents the theory by means of an ASP solver and returned to the user as sets of ground first-order literals. As this type of representation is often cumbersome...

Answer-set programming (ASP) is an established paradigm for declarative problem solving, yet comparably little work on testing of answer-set programs has been done so far. In a recent paper, foundations for structure-based testing of answer-set programs building on a number of coverage notions have been proposed. In this paper, we develop a framewo...

In the object-oriented world, much effort is spent into the development of dedicated tools to ease programming and to prevent programming errors. Recently, the techniques of model-driven engineering (MDE) have been proven especially valuable to manage the complexity of modern software systems during the software development process. In the world o...

While the purpose of conventional proof calculi is to axiomatise the set of valid sentences of a logic, refutation systems axiomatise the invalid sentences. Such systems are relevant not only for proof-theoretic reasons but also for realising deductive systems for nonmonotonic logics. We introduce Gentzen-type refutation systems for two basic three...

In the context of the Semantic Web, several approaches for combining ontologies, given in terms of theories of classical first-order logic and rule bases, have been proposed. They either cast rules into classical logic or limit the interaction between rules and ontologies. Autoepistemic logic (AEL) is an attractive formalism which allows overcoming...

We introduce a framework for interactive stepping through an answer-set program as a means for debugging. In procedural languages, stepping is a widespread and effective debugging strategy. The idea is to gain insight into the behaviour of a program by executing statement by statement, following the program’s control flow. Stepping has not been con...

In many applications, faults are triggered by events that occur in a particular order. Based on the assumption that most bugs are caused by the interaction of a low number of events, Kuhn et al. recently introduced sequence covering arrays (SCAs) as suitable designs for event sequence testing. In practice, directly applying SCAs for testing is ofte...

Recently, the techniques of model-driven engineering (MDE) have been proven valuable to manage the complexity of modern software systems dur-ing the software development process. In the area of answer-set programming (ASP), the focus is set so far on theoretical aspects, applications, and the devel-opment of efficient solvers, reducing the attentio...

Answer-set programming (ASP) is a well-acknowledged paradigm for declarative problem solving, yet comparably little effort has been spent on the investigation of methods to support the development of answer-set programs. In particular, systematic testing of programs, constituting an integral part of conventional software development, has not been d...

Plagiarism detection is a growing need among educational institutions and solutions for different purposes exist. An important field in this direction is detecting cases of source-code plagiarism. In this paper, we present the tool Kato for supporting the detection of this kind of plagiarism in the area of answer-set programming (ASP). Currently, t...

An important issue towards a broader acceptance of answer-set programming (ASP) is the deployment of tools which support the programmer during the coding phase. In particular, methods for debugging an answer-set program are recognised as a crucial step in this regard. Initial work on debugging in ASP mainly focused on propositional programs, yet pr...

Answer-set programming (ASP) is a well-known formalism for declarative problem solving, enjoying a continuously increasing number of diverse applications. However, arguably one of the main challenges for a wider acceptance of ASP is the need of tools, methods, and methodologies that support the actual programming process. In this paper, we review t...

We address the problem of belief change in (nonmonotonic) logic programming under answer set semantics. Unlike previous approaches to belief change in logic programming, our formal techniques are analogous to those of distance-based belief revision in propositional logic. In developing our results, we build upon the model theory of logic programs f...

The tool cc> is an implementation for testing various parameterised notions of program correspondence between logic programs under the answer- set semantics, based on reductions to quantified propositional logic. One such notion is relativised uniform equivalence with projection, which extends standard uniform equivalence via two additional paramet...

In answer-set programming (ASP), many notions of program equivalence have been introduced and formally analysed. A particular line of research in this direction aims at studying conditions under which certain syntactic constructs can be eliminated from programs preserving some given equivalence relation. In this paper, we continue this endeavour in...

Practically all programming languages used in software engineering allow to split a program into several modules. For fully declarative and nonmonotonic logic programming languages, however, the modular structure of programs is hard to realise, since the output of an entire program cannot in general be composed from the output of its component prog...

This paper considers a semantic approach for merging logic programs under answer set semantics. Given logic programs P 1, ..., P n , the goal is to provide characterisations of the merging of these programs. Our formal techniques are based on notions of relative distance between the underlying SE models of the logic programs. Two approaches are exa...

Equilibrium logic is an approach to nonmonotonic reasoning that extends the stable-model and answer-set semantics for logic programs. In particular, it includes the general case of nested logic programs, where arbitrary Boolean combinations are permitted in heads and bodies of rules, as special kinds of theories. In this paper, we present polynomia...

The study of various notions of equivalence between logic programs in the area of answer-set programming (ASP) gained increasing interest in recent years. The main reason for this undertaking is that ordinary equivalence between answer-set programs fails to yield a replacement property similar to the one of classical logic. Although many refined pr...

The study of different notions of equivalence is one of the corner- stones of current research in answer-set programming. This is mainly motivated by the needs of program simplification and modular programming, for which or- dinary equivalence is insufficient. A recently introduced equivalence notion in this context is hyperequivalence, which inclu...

We propose a combination of logic programming under the answer set semantics with the description logics and , which underly the Web ontology languages OWL Lite and OWL DL, respectively. To this end, we introduce description logic programs (or dl-programs), which consist of a description logic knowledge base L and a finite set P of description logi...

Logic programs under answer-set semantics constitute an important tool for declarative problem solving. In recent years, two research issues received growing attention. On the one hand, concepts like loops and elementary sets have been proposed in order to extend Clark's completion for computing answer sets of logic programs by means of proposition...

Answer-set programming (ASP) is widely recognised as a vi- able tool for declarative problem solving. However, there is currently a lack of tools for developing answer-set programs. In particular, providing tools for debugging answer-set pro- grams has recently been identified as a crucial prerequisite for a wider acceptance of ASP. In this paper,...

We address the problem of belief revision in (nonmonotonic) logic programming under answer set semantics: given logic programs P and Q, the goal is to determine a program R that corresponds to the revision of P by Q, denoted P Q. Un- like previous approaches in logic programming, our formal techniques are analogous to those of distance-based belief...

Ordered disjunctions have been introduced as a simple, yet expressive approach for representing preferential knowledge by means of logic programs. The semantics for the resulting language is based on the answer-set semantics, but comes in different variants, depending on the particular interpret ation of preference aggregation associated to the ord...

The combination of rules and ontologies has a central role in the ongoing development of the Semantic Web. In pre- vious work, autoepistemic logic (AEL) was advocated as a uniform host formalism to study different such combinations, enabling comparisons on a common basis. In this paper, we continue this line of research and investigate different em...

The study of various notions of equivalence between logic programs in the area of answer-set programming (ASP) gained increasing interest in recent years. The main reason for this undertaking is the failure of ordinary equivalence between answer-set programs to yield a replacement property similar to the one of classical logic. Although many refine...

We consider the problem of representing arbitrary preferences in causal reasoning and planning systems. In planning, a preference may be seen as a goal or constraint that is desirable, but not necessary, to satisfy. To begin, we define a very general query language for histories, or interleaved sequences of world states and actions. Based on this,...

Answer-set programming (ASP) has become an important paradigm for declarative problem solving in recent years. However, to further improve the usability of answer-set programs, the development of software-engineering tools is vital. In particular, the area of debugging provides a challenge in both theoretical and practical terms. This is due to the...

We present a framework for updating logic programs under the an- swer-set semantics that builds on existing work on preferences in logic program- ming. The approach is simple and general, making use of two distinct comple- mentary techniques: defaultification and preference. While defaultification re- solves potential conflicts by inducing more ans...

Practically all programming languages allow the programmer to split a program into several modules which brings along several advantages in software development. In this paper, we are interested in the area of answer-set programming where fully declarative and nonmonotonic languages are applied. In this context, obtaining a modular structure for pr...

Recent research in answer-set programming (ASP) is concerned with the problem of finding faithful transformations of logic programs under the stable semantics. This is in particular relevant in practice when programs with variables are considered, where such transformations play a basic role in (offline) simplifi- cations of logic programs. So far,...

Recent research in nonmonotonic logic programming under the answer-set semantics focuses on different notions of program equivalence. However, previous results do not address the important classes of stratified programs and its subclass of acyclic (i.e., recursion-free) programs, although they are recognized as important tools for knowledge represe...

For a given semantics, two nonmonotonic theories �1 and �2 can be said to be equivalent if they have the same intended models and strongly (resp., uniformly) equivalent if for any �, �1(� and �2(� are equivalent, whereis a set of sentences (resp., literals). In the general case, no restrictions are placed on the language (signature) of �. Relativis...

Logic programs under answer-set semantics constitute an important tool for declarative problem solving. In recent years, two r esearch issues received growing attention. On the one hand, concepts like loops and elementary sets have been proposed in order to extend Clark's completion for comp uting answer sets of logic programs by means of propositi...

Recent research in answer-set programming (ASP) fo- cuses on different notions of equivalence between pro- grams which are relevant for program optimisation and modular programming. Prominent among these notions is uniform equivalence, which checks whether two pro- grams have the same semantics when joined with an ar- bitrary set of facts. In this...

Answer-set programming (ASP) is an emerging logic-programming paradigm that strictly separates the description of a probl em from its solving methods. Despite its semantic elegance, ASP suffers from a lack of support for program developers. In particular, tools are needed that help engineers in de- tecting erroneous parts of their programs. Unlike...

The system ccT is a tool for testing correspondence between propositional logic programs under the answer-set semantics with respect to different refined notions of program correspondence. The underlying methodology of ccT is to reduce a given correspondence problem to the satisfiability problem of quantified propositional logic and to employ extan...

The language of HEX-programs under the answer-set semantics is designed for interoperating with heterogeneous sources via external atoms and for meta-reasoning via higher-order literals in the context of the semantic Web. As an important technique in managing knowledge bases, the notion of forgetting has received increasing interest in the knowledg...

Answer-set programming (ASP) is a logic programming paradigm for declarative problem solving which gained increasing importance during the last decade. However, so far hardly any tools exist supporting software engineers in developing answer-set programs, and there are no standard methodologies for handling unexpected outcomes of a program. Thus, w...

Ordered disjunctions have recently been introduced as a simple, yet expressive approach for representing preferen-tial knowledge by means of logic programs. The semantics for the resulting language is based on the answer-set se-mantics, but comes in different flavors, depending on the particular notion of preference associated to the disjunction co...

We present the system dlvhex, a solver for HEX-programs, which are nonmonotonic logic programs admitting both higher-order atoms as well as external atoms. Higher-order features are widely acknowledged as being useful for various tasks, including meta-reasoning. Furthermore, the possibility to exchange knowledge with external sources in a fully dec...

In recent work, a general framework for specifying correspondences between logic programs under the answer-set semantics has been defined. The framework allows to define different notions of equivalence, including well-known notions like strong equivalence as well as refined ones based on the projection of answer sets, where not all parts of an ans...

In recent work, a general framework for specifying correspondences between logic programs under the answer-set semantics has been defined. The framework captures different notions of equivalence, including well-known ones like ordinary, strong, and uniform equivalence, as well as refined ones based on the projection of answer sets where not all par...

In the context of current efforts around Semantic-Web languages, the combination of classical theories in classical first-order logic (and in particular of ontologies in various description logics) with rule languages rooted in logic programming is receiving considerable attention. Existing approaches such as SWRL, dl-programs, and DL + log, differ...

The need for sharing knowledge on the Web—and in particular rules in a standardized format—is an important issue. RuleML [1] has been the most prominent effort in this direction so far. Nonetheless, it turns out that none of the variants available is suitable for expressing nonmonotonic logic programs as used in the answer-set programming (ASP)

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Through the Internet and the World-Wide Web, a vast number of information sources has become available, which offer information on various subjects by different providers, often in heterogeneous formats. This calls for tools and methods for building an advanced information-processing infrastructure. One issue in this area is the selection of suitab...

For realizing the Semantic Web vision, extensive work is underway for getting the layers of its conceived architecture ready. Given that the Ontol- ogy Layer has reached a certain level of maturity with W3C recommendations such as RDF and the OWL Web Ontology Language, current interest focuses on the Rules Layer and its integration with the Ontolog...

We briefly report on the development status of dlvhex, a reasoning engine for HEX-prog- rams, which are nonmonotonic logic programs with higher-order atoms and external atoms. Higher- order features are widely acknowledged as useful for various tasks and are essential in the context of meta-reasoning. Furthermore, the possibility to exchange knowle...

In this paper, we propose a formal framework for specify- ing rule replacements in nonmonotonic logic programs within the answer-set programming paradigm. Of particular interest are replacement schemas retaining specic notions of equiv- alence, among them the prominent notions of strong and uni- form equivalence, which have been introduced as theor...

In recent work, a general framework for specifying program correspondences under the answer-set semantics has been defined. The framework allows to define different notions of equiva- lence, including the well-known notions of strong and uniform equivalence, as well as refined equiv- alence notions based on the projection of answer sets, where not...

This paper continues our earlier work in representing arbitrary preferences in causal reasoning and planning systems, albeit in an oblique fashion. Previously, we de-fined a very general query language relative to histories; from this we specified a second language in which pref-erences on histories are defined. This in turn allowed us to define th...