Federated knowledge base debugging in DL-Lite A

Due to the continuously growing amount of data the federation of different and distributed data sources gained increasing attention. In order to tackle the challenge of federating heterogeneous sources a variety of approaches has been proposed. Especially in the context of the Semantic Web the application of Description Logics is one of the preferred methods to model federated knowledge based on a well-defined syntax and semantics. However, the more data are available from heterogeneous sources, the higher the risk is of inconsistency – a serious obstacle for performing reasoning tasks and query answering over a federated knowledge base. Given a single knowledge base the process of knowledge base debugging comprising the identification and resolution of conflicting statements have been widely studied while the consideration of federated settings integrating a network of loosely coupled data sources (such as LOD sources) has mostly been neglected. In this thesis we tackle the challenging problem of debugging federated knowledge bases and focus on a lightweight Description Logic language, called DL-LiteA, that is aimed at applications requiring efficient and scalable reasoning. After introducing formal foundations such as Description Logics and Semantic Web technologies we clarify the motivating context of this work and discuss the general problem of information integration based on Description Logics. The main part of this thesis is subdivided into three subjects. First, we discuss the specific characteristics of federated knowledge bases and provide an appropriate approach for detecting and explaining contradictive statements in a federated DL-LiteA knowledge base. Second, we study the representation of the identified conflicts and their relationships as a conflict graph and propose an approach for repair generation based on majority voting and statistical evidences. Third, in order to provide an alternative way for handling inconsistency in federated DL-LiteA knowledge bases we propose an automated approach for assessing adequate trust values (i.e., probabilities) at different levels of granularity by leveraging probabilistic inference over a graphical model. In the last part of this thesis, we evaluate the previously developed algorithms against a set of large distributed LOD sources. In the course of discussing the experimental results, it turns out that the proposed approaches are sufficient, efficient and scalable with respect to real-world scenarios. Moreover, due to the exploitation of the federated structure in our algorithms it further becomes apparent that the number of identified wrong statements, the quality of the generated repair as well as the fineness of the assessed trust values profit from an increasing number of integrated sources

Debugging weighted ontologies

We present our work on debugging weighted ontologies. We define this problem as computing a consistent subontology with a maximal sum of ax- iom weights. We present a reformulation of the problem as finding the most prob- able consistent ontology according to a log-linear model and show how existing methods from probabilistic reasoning can be adapted to our problem. We close with a discussion of the possible application of weighted ontology debugging to web scale information extraction

Proceedings of the Second International Workshop on Debugging Ontologies and Ontology Mappings - WoDOOM13

Developing ontologies is not an easy task and, as the ontologies grow in size, they are likely to show a number of defects. Such ontologies, although often useful, also lead to problems when used in semantically-enabled applications. Wrong conclusions may be derived or valid conclusions may be missed. Defects in ontologies can take different forms. Syntactic defects are usually easy to find and to resolve. Defects regarding style include such things as unintended re-dundancy. More interesting and severe defects are the modeling defects which require domain knowledge to detect and resolve such as defects in the structure, and semantic defects such as unsatisfiable concepts and inconsistent ontologies. Further, during the recent years more and more mappings between ontologies with overlapping information have been generated, e.g. using ontology alignment systems, thereby connecting the ontologies in ontology networks. This has led to a new opportunity to deal with defects as the mappings and other ontologies in the network may be used in the debugging of a particular ontology in the network. It also has introduced a new difficulty as the mappings may not always be correct and need to be debugged themselves. The WoDOOM series deals with these issues. This volume contains the pro-ceedings of its second edition: WoDOOM13 - Second International Workshop on Debugging Ontologies and Ontology Mappings held on May 27, 2013 in Montpellier, France. WoDOOM13 was an ESWC 2013 (10th Extended Semantic WebConference) workshop. In his excellent invited talk, Heiner Stuckenschmidt proposed approaches for debugging weighted ontologies. In this generalization of the classical debugging problem, axioms in the ontology to be debugged have weights assigned and the task is to remove axioms from this set such that the resulting model is consistent and the sum of weights is maximal. Further, there were presentations of six full papers. The topics included both detection and repair of defects. Several papers used patterns for the detection. Regarding repairing wrong information, one paper proposed a method for reformulating axioms with the aim to retain as much information as possible. Another paper formalized the repairing of missing information in ontologies as a new abductive reasoning problem. Finally, a recently started EU project was presented in which ontology and mapping management is one of the core components. Two of the papers were selected for republicationin the ESWC 2013 post-proceedings. The editors would like to thank the Program Committee for their work in enabling the timely selection of papers for inclusion in the proceedings. We also appreciate our cooperation with EasyChair as well as our publisher CEURWorkshop Proceedings. May 2013 Patrick Lambrix Guilin Qi Matthew Horridge Bijan Parsi

Proceedings of the Second International Workshop on Debugging Ontologies and Ontology Mappings - WoDOOM13

Developing ontologies is not an easy task and, as the ontologies grow in size, they are likely to show a number of defects. Such ontologies, although often useful, also lead to problems when used in semantically-enabled applications. Wrong conclusions may be derived or valid conclusions may be missed. Defects in ontologies can take different forms. Syntactic defects are usually easy to find and to resolve. Defects regarding style include such things as unintended re-dundancy. More interesting and severe defects are the modeling defects which require domain knowledge to detect and resolve such as defects in the structure, and semantic defects such as unsatisfiable concepts and inconsistent ontologies. Further, during the recent years more and more mappings between ontologies with overlapping information have been generated, e.g. using ontology alignment systems, thereby connecting the ontologies in ontology networks. This has led to a new opportunity to deal with defects as the mappings and other ontologies in the network may be used in the debugging of a particular ontology in the network. It also has introduced a new difficulty as the mappings may not always be correct and need to be debugged themselves. The WoDOOM series deals with these issues. This volume contains the pro-ceedings of its second edition: WoDOOM13 - Second International Workshop on Debugging Ontologies and Ontology Mappings held on May 27, 2013 in Montpellier, France. WoDOOM13 was an ESWC 2013 (10th Extended Semantic WebConference) workshop. In his excellent invited talk, Heiner Stuckenschmidt proposed approaches for debugging weighted ontologies. In this generalization of the classical debugging problem, axioms in the ontology to be debugged have weights assigned and the task is to remove axioms from this set such that the resulting model is consistent and the sum of weights is maximal. Further, there were presentations of six full papers. The topics included both detection and repair of defects. Several papers used patterns for the detection. Regarding repairing wrong information, one paper proposed a method for reformulating axioms with the aim to retain as much information as possible. Another paper formalized the repairing of missing information in ontologies as a new abductive reasoning problem. Finally, a recently started EU project was presented in which ontology and mapping management is one of the core components. Two of the papers were selected for republicationin the ESWC 2013 post-proceedings. The editors would like to thank the Program Committee for their work in enabling the timely selection of papers for inclusion in the proceedings. We also appreciate our cooperation with EasyChair as well as our publisher CEURWorkshop Proceedings. May 2013 Patrick Lambrix Guilin Qi Matthew Horridge Bijan Parsi

Proceedings of the Second International Workshop on Debugging Ontologies and Ontology Mappings - WoDOOM13

Developing ontologies is not an easy task and, as the ontologies grow in size, they are likely to show a number of defects. Such ontologies, although often useful, also lead to problems when used in semantically-enabled applications. Wrong conclusions may be derived or valid conclusions may be missed. Defects in ontologies can take different forms. Syntactic defects are usually easy to find and to resolve. Defects regarding style include such things as unintended re-dundancy. More interesting and severe defects are the modeling defects which require domain knowledge to detect and resolve such as defects in the structure, and semantic defects such as unsatisfiable concepts and inconsistent ontologies. Further, during the recent years more and more mappings between ontologies with overlapping information have been generated, e.g. using ontology alignment systems, thereby connecting the ontologies in ontology networks. This has led to a new opportunity to deal with defects as the mappings and other ontologies in the network may be used in the debugging of a particular ontology in the network. It also has introduced a new difficulty as the mappings may not always be correct and need to be debugged themselves. The WoDOOM series deals with these issues. This volume contains the pro-ceedings of its second edition: WoDOOM13 - Second International Workshop on Debugging Ontologies and Ontology Mappings held on May 27, 2013 in Montpellier, France. WoDOOM13 was an ESWC 2013 (10th Extended Semantic WebConference) workshop. In his excellent invited talk, Heiner Stuckenschmidt proposed approaches for debugging weighted ontologies. In this generalization of the classical debugging problem, axioms in the ontology to be debugged have weights assigned and the task is to remove axioms from this set such that the resulting model is consistent and the sum of weights is maximal. Further, there were presentations of six full papers. The topics included both detection and repair of defects. Several papers used patterns for the detection. Regarding repairing wrong information, one paper proposed a method for reformulating axioms with the aim to retain as much information as possible. Another paper formalized the repairing of missing information in ontologies as a new abductive reasoning problem. Finally, a recently started EU project was presented in which ontology and mapping management is one of the core components. Two of the papers were selected for republicationin the ESWC 2013 post-proceedings. The editors would like to thank the Program Committee for their work in enabling the timely selection of papers for inclusion in the proceedings. We also appreciate our cooperation with EasyChair as well as our publisher CEURWorkshop Proceedings. May 2013 Patrick Lambrix Guilin Qi Matthew Horridge Bijan Parsi