Johannes Oetsch

Catching the ouroboros: On debugging non-ground answer-set programs

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 practical debuggers need to handle programs with variables as well. In this paper, we discuss a debugging technique that is directly geared towards non-ground programs. Following previous work, we address the central debugging question why some interpretation is not an answer set. The explanations provided by our method are computed by means of a meta-programming technique, using a uniform encoding of a debugging request in terms of ASP itself. Our method also permits programs containing comparison predicates and integer arithmetics, thus covering a relevant language class commonly supported by all state-of-the-art ASP solvers.

The Fourth Answer Set Programming Competition: Preliminary Report

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.

Applications of Declarative Programming and Knowledge Management

Invited Talk.- A Guide for Manual Construction of Difference-List Procedures.- Constraints.- Linear Weighted-Task-Sum - Scheduling Prioritized Tasks on a Single Resource.- Efficient Edge-Finding on Unary Resources with Optional Activities.- Encoding of Planning Problems and Their Optimizations in Linear Logic.- Constraint-Based Timetabling System for the German University in Cairo.- Databases and Data Mining.- Squash: A Tool for Analyzing, Tuning and Refactoring Relational Database Applications.- Relational Models for Tabling Logic Programs in a Database.- Integrating XQuery and Logic Programming.- Causal Subgroup Analysis for Detecting Confounding.- Using Declarative Specifications of Domain Knowledge for Descriptive Data Mining.- Extensions of Logic Programming.- Integrating Temporal Annotations in a Modular Logic Language.- Visual Generalized Rule Programming Model for Prolog with Hybrid Operators.- The Kiel Curry System KiCS.- Narrowing for First Order Functional Logic Programs with Call-Time Choice Semantics.- Java Type Unification with Wildcards.- System Demonstrations.- Testing Relativised Uniform Equivalence under Answer-Set Projection in the System cc???.- spock: A Debugging Support Tool for Logic Programs under the Answer-Set Semantics.

Stepping through an answer-set program

We introduce a framework for interactive stepping through an answerset 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 programs control flow. Stepping has not been considered for answer-set programs so far, presumably because of their lack of a control flow. The framework we provide allows for stepwise constructing interpretations following the users intuition on which rule instances to become active. That is, we do not impose any ordering on the rules but give the programmer the freedom to guide the stepping process. Due to simple syntactic restrictions, each step results in a state that guarantees stability of the intermediate interpretation. We present how stepping can be started from breakpoints as in conventional programming and discuss how the approach can be used for debugging using a running example.

On Testing Answer-Set Programs

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 discussed for ASP thus far. In this paper, we fill this gap and develop notions enabling the structural testing of answer-set programs, i.e., we address testing based on test cases that are chosen with respect to the internal structure of a given answer-set program. More specifically, we introduce different notions of coverage that measure to what extent a collection of test inputs covers certain important structural components of the program. In particular, we introduce metrics corresponding to path and branch coverage from conventional testing. We also discuss complexity aspects of the considered notions and give strategies how test inputs that yield increasing (up to total) coverage can be automatically generated.

Random vs. structure-based testing of answer-set programs: an experimental comparison

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 framework for testing answer-set programs based on this work and study how good the structure-based approach to test input generation is compared to random test input generation. The results indicate that random testing is quite ineffective for some benchmarks, while structurebased techniques catch faults with a high ratemore consistently also in these cases.

The SeaLion has Landed: An IDE for Answer-Set Programming—Preliminary Report

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 techniques have to be developed that suit the requirements of the answer-set semantics and meet the constraints of practical applicability. In this respect, SeaLion benefits from the research results of a project on methods and methodologies for answer-set program development in whose context SeaLion is realised. Currently, the tool provides source-code editors for the languages of Gringo and DLV that offer syntax highlighting, syntax checking, refactoring functionality, and a visual program outline. Further implemented features are a documentation generator, support for external solvers, and visualisation as well as visual editing of answer sets. SeaLion comes as a plugin of the popular Eclipse platform and provides itself interfaces for future extensions of the IDE.

Kara: A System for Visualising and Visual Editing of Interpretations for Answer-Set Programs

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 for the user to interpret, tools like ASPVIZ and IDPDraw were developed that allow for visualising answer sets. The tool Kara, introduced in this paper, follows these approaches, using ASP itself as a language for defining visualisations of interpretations. Unlike existing tools that position graphic primitives according to static coordinates only, Kara allows for more high-level specifications, supporting graph structures, grids, and relative positioning of graphical elements. Moreover, generalising the functionality of previous tools, Kara provides modifiable visualisations such that interpretations can be manipulated by graphically editing their visualisations. This is realised by resorting to abductive reasoning techniques using ASP itself. Kara is part of SeaLion, an integrated development environment (IDE) for ASP.

SeaLion: An eclipse-based IDE for answer-set programming with advanced debugging support

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 realised in the context of a research project whose goal is the development of techniques to support the practical coding process of answer-set programs. In this respect, SeaLion is the first IDE for ASP that provides debugging features that work for real-world answer-set programs and supports the rich languages of modern answer-set solvers. Indeed, SeaLion implements a stepping-based debugging approach that allows the developer to quickly track down programming errors by simply following his or her intuitions on the intended semantics. Besides that, SeaLion supports ASP development using model-driven engineering techniques including domain modelling with extended UML class diagrams and visualisation of answer sets in corresponding instance diagrams. Moreover, customised visualisation as well as visual editing of answer sets is realised by the Kara plugin of SeaLion . Further implemented features are a documentation generator based on the Lana annotation language, support for external solvers, and interoperability with external tools. SeaLion comes as a plugin of the popular Eclipse platform and provides interfaces for future extensions of the IDE.

VIDEAS: a development tool for answer-set programs based on model-driven engineering technology

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 of answer-set programming (ASP), the situation is different. Much effort is invested into the development of efficient solvers, but the pragmatics of programming itself has not received much attention and more tool support to ease the actual programming phase would be desirable. To address this issue, we introduce the tool VIDEAS which graphically supports the partial specification of answer-set programs, applying technologies provided by MDE.