Prof. Dr. Ralf Möller
Software, Technology and Systems Group (STS),
Hamburg University of Technology (TUHH)


Publications


2012


Volker Haarslev, Kay Hidde, Ralf Möller, and Michael Wessel. The RacerPro knowledge representation and reasoning system. Semantic Web Journal, 3(3):267–277, 2012.
Bibtex entry  Paper (PDF)

Abstract

RacerPro is a software system for building applications based on ontologies. The backbone of RacerPro is a description logic reasoner. It provides inference services for terminological knowledge as well as for representations of knowledge about individuals. Based on new optimization techniques and techniques that have been developed in the research field of description logics throughout the years, a mature architecture for typical-case reasoning tasks is provided. The system has been used in hundreds of research projects and industrial contexts throughout the last twelve years. W3C standards as well as detailed feedback reports from numerous users have influenced the design of the system architecture in general, and have also shaped the RacerPro knowledge representation and interface languages. With its query and rule languages, RacerPro goes well beyond standard inference services provided by other OWL reasoners.


Özgür L. Özçep, Rolf Grütter, and Ralf Möller. Dynamics of a Nearness Relation—First Results. In Mehul Bhatt, Hans W. Guesgen, and Ernest Davis, editors, Proceedings of the International Workshop on Spatio-Temporal Dynamics (STeDy 2012), 2012.
Bibtex entry  Paper (PDF)

Abstract

The system of administrative units for a state like Switzerland can be formally described by a totally ordered set of nested partitions where, e.g., the municipalities make up a finer partition than the partition induced by districts. Based on these partitions one can define binary non-symmetric nearness relations between regions in which the second argument determines the granularity (or the scaling level) w.r.t. which the first-argument region is to be considered near or not. The logical properties of such nearness relations, especially w.r.t. their relation to proximity relations, have been worked out in the authors’ contribution to ECAI 2012. Referring to these properties, in this paper we extend the investigation to the dynamics of the nearness relation. In particular, we investigate how a change within the total order of partitions (e.g., two municipalities are merged) affects the induced nearness relation.


Özgür L. Özçep, Rolf Grütter, and Ralf Möller. Nearness Rules and Scaled Proximity. In Proc. ECAI 2012, 20th European Conference on Artificial Intelligence, pages 636–641, 2012.
Bibtex entry  Paper (PDF)

Abstract

An artificial intelligence system that processes geothematic data would profit from a (semi-)formal or controlled natural language interface that incorporates concepts for nearness. Though there already exists logical-engineering approaches giving sufficient conditions for nearness relations, we show within a logical analysis that these suffer from some deficiencies. Non-engineering approaches to nearness such as the abstract mathematical approach based on proximity spaces do not deal with the implementation aspects but axiomatically formalize intuitions on nearness relations and provide insights on their nature. Combining the ideas of the engineering approach with the mathematical approach of proximity spaces, we define and analyze new nearness relations that provide a good compromise between implementation needs and the need for an appropriate approximation of the natural nearness concept.


Özgür L. Özçep, Rolf Grütter, and Ralf Möller. Nearness Rules and Scaled Proximity. Technical report (extended version of a paper accepted for publication at ECAI 2012), Institute for Softwaresysteme (STS), Hamburg University of Technology, 2012. Available online at http://www.sts.tu-harburg.de/tech-reports/papers.html.
Bibtex entry  Paper (PDF)

Abstract

An artificial intelligence system that processes geo-thematic data would profit from a (semi-)formal or controlled natural language interface that incorporates concepts for nearness. Though there already exists logical-engineering approaches giving sufficient conditions for nearness relations, we show within a logical analysis that these suffer from some deficiencies. Non-engineering approaches to nearness such as the abstract mathematical approach based on proximity spaces do not deal with the implementation aspects but axiomatically formalize intuitions on nearness relations and provide insights on their nature. Combining the ideas of the engineering approach with the mathematical approach of proximity spaces, we define and analyze new nearness relations that provide a good compromise between implementation needs and the need for an appropriate approximation of the natural nearness concept.


Özgür L. Özçep and Ralf Möller. Combining DL-Lite with Spatial Calculi for Feasible Geo-thematic Query Answering. In Yevgeny Kazakov, Domenico Lembo, and Frank Wolter, editors, Proceedings of the 25th Iternational Workshop on Description Logics (DL 2012), volume 846, 2012.
Bibtex entry  Paper (PDF)

Abstract

First order logic (FOL) rewritability is a desirable feature for query answering over geo-thematic ontologies because in most geoprocessing scenarios one has to cope with large data volume. Hence, there is a need for combined geo-thematic logics that provide a sufficiently expressive query language allowing for FOL rewritability. The DL-Lite family of description logics is tailored towards FOL rewritability of query answering for unions of conjunctive queries, hence it is a suitable candidate for the thematic component of a combined geo-thematic logic. We show that a weak coupling of DL-Lite with the expressive region connection calculus RCC8 allows for FOL rewritability under a spatial completeness condition for the ABox. Stronger couplings allowing for FOL rewritability are possible only for spatial calculi as weak as the low-resolution calculus RCC2. Already a strong combination of DL-Lite with the low-resolution calculus RCC3 does not allow for FOL rewritability.


Özgür Lütfü Özçep and Ralf Möller. Computationally Feasible Query Answering over Spatio-thematic Ontologies. In Prof. The Fourth International Conference on Advanced Geographic Information Systems, Applications, and Services, GEOProcessing 2012, 2012.
Bibtex entry  Paper (PDF)

Abstract

Providing query answering facilities at the conceptual level of a geographic data model requires deduction, and deduction in geographical information systems (GIS) is a demanding task due to the size of the data that are stored in secondary memory. In particular, this is the case for deductive query answering w.r.t. spatio-thematic ontologies, which provide a logical conceptualization of an application domain involving geographic data. For specific logics (so-called lightweight description logics) and query languages (conjunctive queries) the query answering problem can be solved by compiling the ontology-based query into an SQL query that is posed to the database. Thus, ontology-based query answering becomes as feasible as standard database query answering. In the literature, this kind of query answering by compilation is formalized using the notion of first-order logic (FOL) rewritability. In this paper we show that lightweight description logics such as DL-Lite can be combined with spatial calculi such as the region connection calculus such that FOL rewritability is retained and the expressive power is sufficient for modeling important aspects of GIS data.


Özgür Lütfü Özçep and Ralf Möller. Scalable Geo-thematic Query Answering. In Proc. International Semantic Web Conference (ISWC 2012), pages 658–673, 2012.
Bibtex entry  Paper (PDF)

Abstract

First order logic (FOL) rewritability is a desirable feature for query answering over geo-thematic ontologies because in most geoprocessing scenarios one has to cope with large data volumes. Hence, there is a need for combined geo-thematic logics that provide a sufficiently expressive query language allowing for FOL rewritability. The DL-Lite family of description logics is tailored towards FOL rewritability of query answering for unions of conjunctive queries, hence it is a suitable candidate for the thematic component of a combined geo-thematic logic. We show that a weak coupling of DL-Lite with the expressive region connection calculus RCC8 allows for FOL rewritability under a spatial completeness condition for the ABox. Stronger couplings allowing for FOL rewritability are possible only for spatial calculi as weak as the low-resolution calculus RCC2. Already a strong combination of DL-Lite with the low-resolution calculus RCC3 does not allow for FOL rewritability.


Sebastian Wandelt and Ralf Möller. Towards ABox Modularization of Semi-expressive Description Logics. Journal of Applied Ontology, 7(2):133–167, 2012.
Bibtex entry  Paper (PDF)

Abstract

In the last years, the vision of the Semantic Web fostered the interest in reasoning over large and very large sets of assertional statements in knowledge bases. Traditional tableau-based reasoning systems perform bad answering queries over large data sets, because these reasoning systems are based on efficient use of main memory data structures. Increasing expressivity and worstcase complexity further tighten the memory burden. The purpose of our work is to investigate how to release the main memory burden from tableau-based reasoning systems and perform efficient instance checking over SHI-knowledge bases. The key idea is to reduce instance checking for an individual in a knowledge base to smaller subsets of relevant axioms. Modularization techniques are introduced and further refined in order to increase the granularity of modules. For evaluation purposes, experiments on benchmark and real world knowledge bases are carried out. The principal conclusion is that the main memory burden for instance checking can be released from tableau-based reasoning systems for semi-expressive Description Logics, by using modularization techniques.


Acknowledgments
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