Semantic Rhine April 2008
From semanticweb.org
| Semantic Rhine April 2008 | |
|---|---|
Semantic Rhine April 2008
| |
| Start | April 15 2008 (iCal) |
| End | April 15 2008 |
| Location | |
| City: | Koblenz |
| Country: | Germany |
Event in series Semantic Rhine
| |
The April 2008 meeting of the Semantic Rhine gatherings took place at the University of Koblenz.
[edit] Agenda
See below for detailed abstracts.
| 10:45–11:10 | Jürgen Angele | New Product Features of OntoStudio and OntoBroker |
| 11:10–11:35 | Michael Meier, Thomas Hornung | Some Aspects of SPARQL |
| Coffee | ||
| 11:45–12:10 | Fang Wei | dRDF: Entailment for Domain-Restricted RDF |
| 12:10–12:35 | Simon Schenk | On the Semantics of Caching in the Semantic Web |
| Lunch | ||
| 13:35–14:00 | Anne Schlicht | Distributed Resolution for Description Logics - First Results |
| 14:00–14:25 | Claudia Obermaier | Precompilation of Description Logic Tboxes |
| Coffee | ||
| 14:35–15:00 | Sebastian Rudolph | OBDD-based Tbox Reasoning in SHIQ |
| 15:00–15:25 | Markus Krötzsch | Description Logic Rules |
| Coffee + Poster Session | ||
| 16:00–16:25 | Guilin Qi | Inconsistency Handling in Description Logics |
| 16:25–16:50 | Christian Meilicke | Applying Logical Constraints to Ontology Matching |
[edit] Talks
[edit] New Product Features of OntoStudio and OntoBroker
Die nächsten Releases von OntoStudio und OntoBroker stehen vor der Tür und bringen eine ganze Reihe an Neuerungen und zusätzlichen Features. Diese sollen in dem Vortrag jeweils kurz skizziert werden.
[edit] Some Aspects of SPARQL
By Thomas Hornung, Norbert Küchlin, Georg Lausen, Michael Meier, Michael Schmidt
In the first part of the talk we will elaborate on adding key and foreign key constraints to RDF and on checking these constraints using SPARQL. In the second part we will report on a performance benchmark of SPARQL and will point out first implications of applying the benchmark to some SPARQL machines. We will also report on executing SPARQL queries on top of relational RDF storage backends.
This talk is based on the works Relational Databases in RDF: Keys and Foreign Keys and SPARQLing Constraints for RDF
[edit] dRDF: Entailment for Domain-Restricted RDF
By Reinhard Pichler, Axel Polleres, Fang Wei, Stefan Woltran
We introduce domain-restricted RDF (dRDF) which allows to associate an RDF graph with a fixed, finite domain that interpretations for it may range over. We show that dRDF is a real extension of RDF and discuss impacts on the complexity of entailment in dRDF. The entailment problem represents the key reasoning task for RDF and is well known to be NP-complete. Remarkably, we show that the restriction of domains in dRDF raises the complexity of entailment from NP to 
-completeness. In order to lower complexity of entailment for both domain-restricted and unrestricted graphs, we take a closer look at the graph structure. For cases where the structure of RDF graphs is restricted via the concept of bounded treewidth, we prove that the entailment is tractable for unrestricted graphs and coNP-complete for domain-restricted graphs.
[edit] On the Semantics of Caching in the Semantic Web
By Simon Schenk
Reasoning in a distributed environment like the Semantic Web raises the problem that resources may become unavailable. To reduce problems resulting from unavailable sources to improve performance, caching can be used. Caches, however can contain imprecise or outdated information. We propose to distinguish between certain and cached information when reasoning on the semantic web by extending the well known \four lattice of truth and knowledge orders. We discuss how users can be offered additional information about the reliability of inferred information, based on the availability of the corresponding information sources. Based on this extended framework we redefine the well founded semantics for rule based systems and investigate the resulting language.
[edit] Distributed Resolution for Description Logics – First Results
The use of Description Logic as the basis for Semantic Web Languages has led to new requirements with respect to scalable and non-standard reasoning. Description logic is a decidable fragment of FOL but still, the standard reasoning tasks are of exponential complexity, satisfiability and subsumption tests are often intractable on large ontologies. Existing large ontologies have a modular structure like networks of linked ontologies, caused by the development process. However, current reasoning approaches do scarcely take advantage of this structure. The available reasoners do not exploit parallel computation and scalability improvements enabled by distributed reasoning. In this paper, we lay the foundation for developing distributed reasoning methods by showing that the description logic fragment ALC can be distributed. We propose a distributed, complete and terminating algorithm that decides satisfiability of terminologies in ALC. The algorithm is based on recent results on applying resolution to description logics. We show that the resolution procedure proposed by Motik can be distributed amongst multiple resolution solvers by assigning unique sets of literals to individual solvers. This provides the basis for a Highly scalable reasoning infrastructure for Description logics.
[edit] Precompilation of Description Logic Tboxes
Knowledge compilation is a common technique for propositional logic knowledge bases. The idea is to transform a given knowledge base into a special normal form, for which queries can be answered efficiently. This precompilation step is very expensive but it only has to be performed once. We propose to apply this technique to knowledge bases defined in Description Logics. For this, we introduce a normal form, called linkless concept descriptions, for ALC concepts. Further we present an algorithm, based on path dissolution, which can be used for this precompilation step. We discuss an efficient satisfiability test as well as a subsumption test for precompiled concept descriptions. Finally we show how to extend this approach in order to precompile Tboxes and to use the precompiled Tboxes for efficient Tbox reasoning.
[edit] OBDD-based Tbox Reasoning in SHIQ
By Sebastian Rudolph, Markus Krötzsch, Pascal Hitzler
We present a new algorithm for reasoning in the description logic SHIQ, which is the most prominent fragment of the Web Ontology Language OWL. The algorithm is based on ordered binary decision diagrams (OBDDs) as a datastructure for storing and operating on large model representations. We thus draw on the success and the proven scalability of OBDD-based systems. To the best of our knowledge, we present the very first algorithm for using OBDDs for reasoning with general TBoxes.
This talk is based on the work Terminological Reasoning in SHIQ with Ordered Binary Decision Diagrams
[edit] Description Logic Rules
By Markus Krötzsch, Sebastian Rudolph, Pascal Hitzler
In this talk, we give a short overview of a number of recent results relating expressive description logics and (first-order logic) rules in a natural and computatinally feasible way. In particular, we summarise the results on DL rules and the tractable DL-based rule language ELP.
This talk is based on the works Expressive Tractable Description Logics based on SROIQ Rules, ELP: Tractable Rules for OWL 2, and All Elephants are Bigger than All Mice
[edit] Inconsistency Handling in Description Logics
By Guilin Qi
In this talk, I will give a short survey of the work on inconsistency handling in description logics that we have done in NeOn project. I will first provide the motivations of inconsistency handling in description logics. Then I give a brief overview of two classes of methods for dealing with inconsistency which have been developed in NeOn project. Finally, I will conclude with some future directions.
[edit] Applying Logical Constraints to Ontology Matching
Automatically discovering semantic relations between ontologies is an important task with respect to overcoming semantic heterogeneity on the semantic web. Ontology matching systems, however, often produce erroneous mappings. In this paper we propose a method for optimizing precision and recall of existing matching systems. The principle of this method is based on the idea that it is possible to infer logical constraints by comparing subsumption relations between concepts of the ontologies to be matched. In order to verify this principle we implemented a system that uses our method as basis for optimizing mappings. We generated a set of synthetic ontologies and corresponding defective mappings and studied the behavior of our method with respect to the properties of the matching problem. The results show that our strategy actually improves the quality of the generated mappings
[edit] Posters
[edit] Ontology Mapping with MDE
The alignment of different ontologies requires the specification, representation and execution of translation rules. The rules need to integrate translations at the lexical, the syntactic and the semantic layer requiring semantic reasoning as well as low-level specification of adhoc conversions of data. Existing formalisms for representing translation rules cannot cover the representation needs of these three layers in one model. We propose a metamodel-based representation of ontology alignments that integrate semantic translations using description logics and lower level translation specifications into one model of representation for ontology alignments.
[edit] Probabilistic Ontology mappings
Creating mappings between ontologies is a common way of approaching the semantic heterogeneity problem on the SemanticWeb. To fit into the landscape of semantic web languages, a suitable, logic-based representation formalism for mappings is needed. We argue that such a formalism has to be able to deal with uncertainty and inconsistencies in automatically created mappings. We analyze the requirements for such a formalism, and we propose a novel approach to probabilistic description logic programs as such a formalism, which tightly combines disjunctive logic programs under the answer set semantics with both description logics and Bayesian probabilities. We define the language, and we show that it can be used to resolve inconsistencies and merge mappings from different matchers based on the level of confidence assigned to different rules. We further discuss different options of implementing question answering in the context of probabilistic ontology mappings
[edit] Approximate Reasoning with Screech
Applications of expressive ontology reasoning for the Semantic Web require scalable algorithms for deducing implicit knowledge from explicitly given knowledge bases. Besides the development of more efficient such algorithms, awareness is rising that approximate reasoning solutions will be helpful and needed for certain application domains. In this paper, we present a comprehensive overview of the \textsc{Screech} approach to approximate reasoning with OWL ontologies, which is based on the KAON2 algorithms, facilitating a compilation of OWL DL TBoxes into Datalog, which is tractable in terms of data complexity. We present three different instantiations of the \textsc{Screech} approach, and report on experiments which show that a significant gain in efficiency can be achieved.
