Journal of Logic and Computation - recent issues

Special Issue on Ontology Dynamics

Flouris, G., d'Aquin, M., Antoniou, G., Pan, J., Plexousakis, D. — Mon, 21 Sep 2009 08:00:31 PDT

Base Revision for Ontology Debugging

Ribeiro, M. M., Wassermann, R. — Mon, 21 Sep 2009 08:00:31 PDT

Belief Revision deals with the problem of adding new information to a knowledge base in a consistent way. Ontology Debugging, on the other hand, aims to find the axioms in a terminological knowledge base which caused the base to become inconsistent. In this article, we propose a belief revision approach in order to find and repair inconsistencies in ontologies represented in some description logic (DL). As the usual belief revision operators cannot be directly applied to DLs, we propose new operators that can be used with more general logics and show that, in particular, they can be applied to the logics underlying OWL-DL and Lite.

On Instance-level Update and Erasure in Description Logic Ontologies

De Giacomo, G., Lenzerini, M., Poggi, A., Rosati, R. — Mon, 21 Sep 2009 08:00:31 PDT

A Description Logic (DL) ontology is constituted by two components, a TBox that expresses general knowledge about the concepts and their relationships, and an ABox that describes the properties of individuals that are instances of concepts. We address the problem of how to deal with changes to a DL ontology, when these changes affect only the ABox, i.e. when the TBox is considered invariant. We consider two basic changes, namely instance-level update and instance-level erasure, roughly corresponding to the addition and the deletion of a set of facts involving individuals. We characterize the semantics of instance-level update and erasure on the basis of the approaches proposed by Winslett and by Katsuno and Mendelzon. Interestingly, DLs are typically not closed with respect to instance-level update and erasure, in the sense that the set of models corresponding to the application of any of these operations to a knowledge base in a DL $$\mathcal{L}$$ may not be expressible by ABoxes in $$\mathcal{L}$$. In particular, we show that this is true for DL-Lite$$\mathcal{F}$$, a tractable DL that is oriented towards data-intensive applications. To deal with this problem, we first introduce DL-Lite$$\mathcal{FS}$$, a DL that minimally extends DL-Lite$$\mathcal{F}$$ and is closed with respect to instance-level update, and present a polynomial algorithm for computing instance-level update in this logic. Then, we provide a principled notion of best approximation with respect to a fixed language $$\mathcal{L}$$ of instance-level update and erasure, and exploit the algorithm for instance-level update for DL-Lite$$\mathcal{FS}$$ to get polynomial algorithms for approximated instance-level update and erasure for DL-Lite$$\mathcal{F}$$. These results confirm the nice computational properties of DL-Lite$$\mathcal{F}$$ for data intensive applications, even where information about instances is not only read, but also written.

Trust-based Revision for Expressive Web Syndication

Golbeck, J., Halaschek-Wiener, C. — Mon, 21 Sep 2009 08:00:31 PDT

Interest in web-based syndication systems has been growing as information streams onto the web at an increasing rate. Technologies, like the standard Semantic Web languages RDF and OWL, make it possible to create expressive representations of the content of publications and subscriptions in a syndication framework. Because these languages are based in description logics, this representation allows the application to reasoning to make more precise matching of user interests with published information. A challenge to this approach is that the consistency of the underlying knowledge base must be maintained for these techniques to work. With the frequent addition of information from new publications, it is likely that inconsistencies will arise. There are many potential mechanisms for choosing which inconsistent information to discard from the KB to regain consistency; in the case of news syndication, we argue keeping the most trusted information is important for generating the most valuable matches. Thus, in this article, we present algorithms for belief-base revision, and specifically look at the user's trust in the information sources as a metric for deciding what to keep in the KB and what to remove.

Category-based Equational Reasoning: An Approach to Ontology Integration

Geldart, J., Song, W. — Mon, 21 Sep 2009 08:00:31 PDT

Incorporating dynamic, general computational knowledge into Semantic Web ontologies is becoming increasingly important. The Semantic Web is now being used to model the behaviour of highly dynamic domains such as web-services, but current approaches to ontologies [such as Web Ontology Language (OWL)] are static and crisp. This article develops a new semantics for Resource Description Framework (RDF) based upon ideas from category theory. In so doing, we not only decouple RDF's semantics from crisp set theory, opening the door to easy adoption of models of uncertainty, but also allow the use of equational reasoning in a principled fashion within RDF. We demonstrate the abilities of equational reasoning, whilst explaining its semantic principles in terms of our RDF category, using an example from the domain of genealogy. We further develop an algebra of (equational) ontologies which allows us to express fine relations between ontologies and to build more complex ontologies out of simpler ones.

Reasoning Support for Mapping Revision

Meilicke, C., Stuckenschmidt, H., Tamilin, A. — Mon, 21 Sep 2009 08:00:31 PDT

Finding correct semantic correspondences between heterogeneous ontologies is one of the most challenging problems in the area of semantic web technologies. As manually constructing such mappings is not feasible in realistic scenarios, a number of automatic matching tools have been developed that propose mappings based on general heuristics. As these heuristics often produce incorrect results, a manual revision is inevitable in order to guarantee the quality of generated mappings. Experiences with benchmarking matching systems revealed that the manual revision of mappings is still a very difficult problem because it has to take the semantics of the ontologies as well as interactions between mappings into account. In this article, we propose methods for supporting human experts in the task of revising automatically created mappings. In particular, we present non-standard reasoning methods for detecting and propagating implications of expert decisions on the correctness of a mapping.

A Multi-Agent System for Dynamic Ontologies

Ottens, K., Hernandez, N., Gleizes, M.-P., Aussenac-Gilles, N. — Mon, 21 Sep 2009 08:00:31 PDT

In the article, we present Dynamo (an acronym of DYNAMic Ontologies), a tool based on an adaptive multi-agent system to construct and maintain an ontology from a domain-specific set of texts. The originality of our proposal is that the adaptative multi-agent system is used both to represent the ontology itself and to produce the ontology. This enables us to propose a system building and maintaining dynamically an ontology according to interactions with the user (also called the ontologist). We present our system and the mechanisms used to build and maintain the ontology from the texts and for the interactions with the ontologist. We also give results of the evaluation of our system.

Multimedia Interpretation for Dynamic Ontology Evolution

Mon, 21 Sep 2009 08:00:31 PDT

The recent success of distributed and dynamic infrastructures for knowledge sharing has raised the need for semiautomatic/automatic ontology evolution strategies. Ontology evolution is generally defined as the timely adaptation of an ontology to changing requirements and the consistent propagation of changes to dependent artifacts. In this article, we present an ontology evolution approach in the context of multimedia interpretation. Ontology evolution in this context relies on the results obtained through reasoning for the interpretation of multimedia resources, through population of the ontology with new individuals or through enrichment of the ontology with new concepts and new semantic relations. The article analyses the results of interpretation, population and enrichment obtained in evaluation experiments in terms of measures such as precision and recall. The evaluation reveals encouraging results.

Editorial

Costantini, S., Watson, R. — Thu, 23 Jul 2009 00:50:15 PDT

Monotonic Answer Set Programming

Gebser, M., Gharib, M., Mercer, R., Schaub, T. — Thu, 23 Jul 2009 00:50:15 PDT

Answer set programming (ASP) does not allow for incrementally constructing answer sets or locally validating constructions like proofs by only looking at a part of the given program. In this article, we elaborate upon an alternative approach to ASP that allows for incremental constructions. Our approach draws its basic intuitions from the area of default logics. We investigate the feasibility of the concept of semi-monotonicity known from default logics as a basis of incrementality. On the one hand, every logic program has at least one answer set in our alternative setting, which moreover can be constructed incrementally based on generating rules. On the other hand, the approach may produce answer sets lacking characteristic properties of standard answer sets, such as being a model of the given program. We show how integrity constraints can be used to re-establish such properties, even up to correspondence with standard answer sets. Furthermore, we develop an SLD-like proof procedure for our incremental approach to ASP, which allows for query-oriented computations. Also, we provide a characterization of our definition of answer sets via a modification of Clark's completion. Based on this notion of program completion, we present an algorithm for computing the answer sets of a logic program in our approach.

From (Quantified) Boolean Formulae to Answer Set Programming

Stephan, I., Da Mota, B., Nicolas, P. — Thu, 23 Jul 2009 00:50:15 PDT

We propose in this article a translation from quantified Boolean formulae to answer set programming. The computation of a solution of a quantified Boolean formula is then equivalent to the computation of a stable model for a normal logic program. The case of unquantified Boolean formulae is also considered since it is equivalent to the case of quantified Boolean formulae with only existential quantifiers.

A Translation-based Approach to the Verification of Modular Equivalence

Oikarinen, E., Janhunen, T. — Thu, 23 Jul 2009 00:50:15 PDT

The goal of this article is to foster modular program development in answer set programming using a Gaifman-Shapiro-style module architecture. More specifically, a method for verifying the equivalence of logic program modules is devised and proved correct. The idea is to adapt a translation-based verification technique, which was originally devised for complete programs only, for program modules. In addition, optimization strategies are addressed in order to exploit the modular structure of programs in verification tasks. A number of experiments on verification strategies are also conducted using lpeq which implements the verification method for the smodels system. The preliminary experimental results reported in this article suggest that the modularization of equivalence verification leads to potential time savings especially if the modules involved share a common context.

The Significance of Memory Costs in Answer Set Solver Implementation

Brain, M., De Vos, M. — Thu, 23 Jul 2009 00:50:15 PDT

Implementation costs linked to processor memory subsystems (cache miss costs, stalls due to bandwidth limits, etc.) have been shown to be a factor in the performance of a variety of declarative programming tools. This article investigates their impact on answer set solvers and the factors that control them. Experiments independently altering the size and difficulty of input programs allow a qualitative assessment of whether input program or solver design is a greater factor and a quantitative assessment of how much of problem these issues create.A variety of processor performance metrics are recorded and used to provide a detailed picture of what limits solver performance and dispel a number of common misapprehensions.To demonstrate the degree to which these problems can be addressed, smodels-ie is presented. This is a version of the smodels solver with a number of implementation changes to improve cache utilisation, one major aspect of memory costs.

OntoDLV: An ASP-based System for Enterprise Ontologies

Ricca, F., Gallucci, L., Schindlauer, R., Dell'Armi, T., Grasso, G., Leone, N. — Thu, 23 Jul 2009 00:50:15 PDT

Enterprise/Corporate ontologies are widely adopted to conceptualize business enterprise information. In this area, the semantic peculiarities of Answer Set Programming (ASP), like the Closed World Assumption (CWA) and the Unique Name Assumption (UNA), are more appropriate than the OntologyWeb Language (OWL) assumptions, also because such ontologies frequently stem from relational databases, where both CWA and UNA are adopted. This article presents OntoDLV, a system based on ASP for the specification and reasoning on enterprise ontologies. OntoDLV implements a powerful ontology representation language, called OntoDLP, extending (disjunctive) ASP with all the main ontology features including classes, inheritance, relations and axioms. OntoDLP is strongly typed, and includes also complex type constructors, like lists and sets. Importantly, OntoDLV supports a powerful interoperability mechanism with OWL, allowing the user to retrieve information from OWL ontologies, and build rule-based reasoning on top of OWL ontologies. The system is already used in a number of real-world applications including agent-based systems, information extraction, and text classification.

Efficiently Querying RDF(S) Ontologies with Answer Set Programming

Ianni, G., Martello, A., Panetta, C., Terracina, G. — Thu, 23 Jul 2009 00:50:15 PDT

Ontologies are pervading many areas of knowledge representation and management. To date, most research efforts have been spent on the development of sufficiently expressive languages for the representation and querying of ontologies; however, querying efficiency has received attention only recently, especially for ontologies referring to large amounts of data. In fact, it is still uncertain how reasoning tasks will scale when applied on massive amounts of data. This work is a first step toward this setting: it first shows that Resource Description Framework(Schema) [RDF(S)] ontologies can be expressed, without loss of semantics, into Answer Set Programming (ASP). Then, based on a previous result showing that the SPARQL query language (a candidate W3C recommendation for RDF(S) ontologies) can be mapped to a rule-based language, it shows that efficient querying of big ontologies can be accomplished with a database oriented extension of the well known ASP system DLV, which we recently developed. Results reported in the article show that our proposed framework is promising for the improvement of both scalability and expressiveness of available RDF(S) storage and query systems.

Experimental Analysis of Graph-based Answer Set Computation over Parallel and Distributed Architectures

Grossi, G., Marchi, M., Pontelli, E., Provetti, A. — Thu, 23 Jul 2009 00:50:15 PDT

This article presents a distributed version of the adjSolver algorithm for computing the answer sets of logic programs. adjSolver operates a classical branch-and-bound structure; its intrinsic parallelism is exploited to control, with a centralized architecture, the delegation of promising search subspaces to distributed handling agents. adjSolver has been implemented and tested on a Beowulf platform, using MPI message passing. The communication overhead was minimized by adopting a compact representation of the data exchanged among agents and by reusing previously-computed partial solutions.

Connections between Belief Revision, Belief Merging and Social Choice

Gabbay, D., Rodrigues, O., Pigozzi, G. — Thu, 21 May 2009 08:29:40 PDT

Geodesic Revision

Georgatos, K. — Thu, 21 May 2009 08:29:40 PDT

The purpose of this article is to introduce a class of distance-based iterated revision operators generated by minimizing the geodesic distance on a graph. Such operators correspond bijectively to metrics and have a simple finite presentation. As distance is generated by distinguishability, our framework is appropriate for modelling contexts where distance is generated by threshold, and therefore, when measurement is erroneous.

Aggregating Judgements by Merging Evidence

Williamson, J. — Thu, 21 May 2009 08:29:40 PDT

The theory of belief revision and merging has recently been applied to judgement aggregation. In this article I argue that judgements are best aggregated by merging the evidence on which they are based, rather than by directly merging the judgements themselves. This leads to a three-step strategy for judgement aggregation. First, merge the evidence bases of the various agents using some method of belief merging. Second, determine which degrees of belief one should adopt on the basis of this merged evidence base, by applying objective Bayesian theory. Third, determine which judgements are appropriate given these degrees of belief by applying a decision-theoretic account of rational judgement formation.

Aggregating Partially Ordered Preferences

Pini, M. S., Rossi, F., Venable, K. B., Walsh, T. — Thu, 21 May 2009 08:29:40 PDT

Preferences are not always expressible via complete linear orders: sometimes it is more natural to allow for the presence of incomparable outcomes. This may hold both in the agents' preference ordering and in the social order. In this article, we consider this scenario and study what properties it may have. In particular, we show that, despite the added expressivity and ability to resolve conflicts provided by incomparability, classical impossibility results (such as Arrow's theorem, Muller–Satterthwaite's theorem and Gibbard–Satterthwaite's theorem) still hold. We also prove some possibility results, generalizing Sen's theorem for majority voting. To prove these results, we define new notions of unanimity, monotonicity, dictator, triple-wise value-restriction and strategy-proofness, which are suitable and natural generalizations of the classical ones for complete orders.

Non-manipulable Social Welfare Functions when Preferences are Fuzzy

Perote-Pena, J., Piggins, A. — Thu, 21 May 2009 08:29:40 PDT

It is well known that many social decision procedures are manipulable through strategic behaviour. Typically, the decision procedures considered in the literature have been social choice correspondences. In this article, we investigate the problem of constructing a social welfare function that is non-manipulable. In this context, individuals attempt to manipulate a social ordering as opposed to a social choice.

Using techniques from fuzzy set theory, we introduce a class of fuzzy binary relations of which exact binary relations are a special case. Operating within this family enables us to prove an impossibility theorem. This theorem states that all non-manipulable social welfare functions are dictatorial, provided that they are not constant. A proof of this theorem first appeared in Perote-Peña and Piggins (2007, J. Math. Econ., 43, 564–580). This article contains a new proof of this theorem which is considerably simpler than the original. Moreover, we also consider a possibility result which this earlier article neglects.

A General Approach to Aggregation Problems

Daniels, T. R., Pacuit, E. — Thu, 21 May 2009 08:29:40 PDT

We discuss a general approach to judgement aggregation based on lattice theory. Agents choose elements of a lattice, and an aggregation procedure yields a ‘social choice’ based on the individual choices. Settings traditionally studied in social choice theory can be thought of as implicational systems, and lattice theory provides an abstraction of such systems. In fact, traditionally studied settings correspond to certain atomistic lattices in our framework. Our aim is to systematically investigate how properties of a given lattice induce constraints on aggregation procedures that lead up to impossibility theorems. We allow for non-atomistic lattices and this raises some subtle issues. We will discuss how well our framework fits in with the traditional approaches to social choice theory, in particular with respect to generalizations of some of the well known axioms, and go on prove an impossibility result that highlights the role of certain lattice theoretical properties. These properties reflect some of the traditional axioms or other aspects of traditional systems.