Connection-minimal Abduction in EL via Translation to FOL -- Technical Report

Abduction in description logics finds extensions of a knowledge base to makeit entail an observation. As such, it can be used to explain why theobservation does not follow, to repair incomplete knowledge bases, and toprovide possible explanations for unexpected observations. We consider TBoxabduction in the lightweight description logic EL, where the observation is aconcept inclusion and the background knowledge is a TBox, i.e., a set ofconcept inclusions. To avoid useless answers, such problems usually come withfurther restrictions on the solution space and/or minimality criteria that helpsort the chaff from the grain. We argue that existing minimality notions areinsufficient, and introduce connection minimality. This criterion followsOccam's razor by rejecting hypotheses that use concept inclusions unrelated tothe problem at hand. We show how to compute a special class ofconnection-minimal hypotheses in a sound and complete way. Our technique isbased on a translation to first-order logic, and constructs hypotheses based onprime implicates. We evaluate a prototype implementation of our approach onontologies from the medical domain.<br

Reasoning in Description Logic Ontologies for Privacy Management

A rise in the number of ontologies that are integrated and distributed in numerous application systems may provide the users to access the ontologies with different privileges and purposes. In this situation, preserving confidential information from possible unauthorized disclosures becomes a critical requirement. For instance, in the clinical sciences, unauthorized disclosures of medical information do not only threaten the system but also, most importantly, the patient data. Motivated by this situation, this thesis initially investigates a privacy problem, called the identity problem, where the identity of (anonymous) objects stored in Description Logic ontologies can be revealed or not. Then, we consider this problem in the context of role-based access control to ontologies and extend it to the problem asking if the identity belongs to a set of known individuals of cardinality smaller than the number k. If it is the case that some confidential information of persons, such as their identity, their relationships or their other properties, can be deduced from an ontology, which implies that some privacy policy is not fulfilled, then one needs to repair this ontology such that the modified one complies with the policies and preserves the information from the original ontology as much as possible. The repair mechanism we provide is called gentle repair and performed via axiom weakening instead of axiom deletion which was commonly used in classical approaches of ontology repair. However, policy compliance itself is not enough if there is a possible attacker that can obtain relevant information from other sources, which together with the modified ontology still violates the privacy policies. Safety property is proposed to alleviate this issue and we investigate this in the context of privacy-preserving ontology publishing. Inference procedures to solve those privacy problems and additional investigations on the complexity of the procedures, as well as the worst-case complexity of the problems, become the main contributions of this thesis.:1. Introduction 1.1 Description Logics 1.2 Detecting Privacy Breaches in Information System 1.3 Repairing Information Systems 1.4 Privacy-Preserving Data Publishing 1.5 Outline and Contribution of the Thesis 2. Preliminaries 2.1 Description Logic ALC 2.1.1 Reasoning in ALC Ontologies 2.1.2 Relationship with First-Order Logic 2.1.3. Fragments of ALC 2.2 Description Logic EL 2.3 The Complexity of Reasoning Problems in DLs 3. The Identity Problem and Its Variants in Description Logic Ontologies 3.1 The Identity Problem 3.1.1 Description Logics with Equality Power 3.1.2 The Complexity of the Identity Problem 3.2 The View-Based Identity Problem 3.3 The k-Hiding Problem 3.3.1 Upper Bounds 3.3.2 Lower Bound 4. Repairing Description Logic Ontologies 4.1 Repairing Ontologies 4.2 Gentle Repairs 4.3 Weakening Relations 4.4 Weakening Relations for EL Axioms 4.4.1 Generalizing the Right-Hand Sides of GCIs 4.4.2 Syntactic Generalizations 4.5 Weakening Relations for ALC Axioms 4.5.1 Generalizations and Specializations in ALC w.r.t. Role Depth 4.5.2 Syntactical Generalizations and Specializations in ALC 5. Privacy-Preserving Ontology Publishing for EL Instance Stores 5.1 Formalizing Sensitive Information in EL Instance Stores 5.2 Computing Optimal Compliant Generalizations 5.3 Computing Optimal Safe^{\exists} Generalizations 5.4 Deciding Optimality^{\exists} in EL Instance Stores 5.5 Characterizing Safety^{\forall} 5.6 Optimal P-safe^{\forall} Generalizations 5.7 Characterizing Safety^{\forall\exists} and Optimality^{\forall\exists} 6. Privacy-Preserving Ontology Publishing for EL ABoxes 6.1 Logical Entailments in EL ABoxes with Anonymous Individuals 6.2 Anonymizing EL ABoxes 6.3 Formalizing Sensitive Information in EL ABoxes 6.4 Compliance and Safety for EL ABoxes 6.5 Optimal Anonymizers 7. Conclusion 7.1 Main Results 7.2 Future Work Bibliograph

Semantische Informationsintegration - Konzeption eines auf Beschreibungslogiken basierenden Integrationssystems für die Produktentwicklung

Aufgrund der Notwendigkeit, unkontrolliert aufkommende Datenfluten zu beherrschen sowie der steigenden Produktkomplexität resultiert der Handlungsbedarf, skalierbare Informationsintegrationslösungen zu finden, die einen effizienten und kontextbezogenen Zugriff auf Wissen unterstützen. Einsatz eines semantischen Integrationskonzepts in der Produktentwicklung erweitert den Wissensbeschaffungsraum des Ingenieurs enorm und ermöglicht die Interoperabilität heterogener Informationssysteme

Inspecting Java Program States with Semantic Web Technologies

Semantic debugging, as introduced by Kamburjan et al., refers to the practice of applying technologies of the semantic web to query the run-time state of a program and combine it with external domain knowledge. This master thesis aims to take the first step toward making the benefits of semantic debugging available for real-world application development. For this purpose, we implement a semantic debugging tool for the Java programming language, called the Semantic Java Debugger or sjdb. The sjdb tool provides an interactive, command line-based user interface through which users can (1) run Java programs and suspend their execution at user-defined breakpoints, (2) automatically extract RDF knowledge bases with description logic semantics that describe the current state of the program, (3) optionally supplement the knowledge base with external domain knowledge formalized in OWL, (4) run (semantic) queries on this extended knowledge base, and resolve the query results back to Java objects. As part of this debugging tool, the development of an extraction mechanism for knowledge bases from the states of suspended Java programs is one of the main contributions of this thesis. For this purpose, we also devise an OWL formalization of Java runtime states to structure this extraction process and give meaning to the resulting knowledge base. Moreover, case studies are conducted to demonstrate the capabilities of sjdb, but also to identify its limitations, as well as its response times and memory requirements