Veronika Thost

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Ontology-based data access (OBDA) generalizes query answering in relational databases. It allows to query a database by using the language of an ontology, abstracting from the actual relations of the database. For ontologies formulated in Description Logics of the DL-Lite family, OBDA can be realized by rewriting the query into a classical first-order(More)
Ontology-based data access (OBDA) generalizes query answering in relational databases. It allows to query a database<lb>by using the language of an ontology, abstracting from the actual relations of the database. OBDA can sometimes be<lb>realized by compiling the information of the ontology into the query and the database. The resulting query is(More)
Context-aware applications try to detect specific situations within a changing environment (e.g. a computer system or air traffic observed by radar) in order to react accordingly. To gain information, the environment is observed by sensors (for a computer system, data about its resources is gathered by the operating system), and the results of sensing are(More)
Graph-structured data is used to represent large information collections, called knowledge graphs, in many applications. Their exact format may vary, but they often share the concept that edges can be annotated with additional information, such as validity time or provenance information. Property Graph is a popular graph database format that also provides(More)
Ontology-based data access augments classical query answering over fact bases by adopting the open-world assumption and by including domain knowledge provided by an ontology. We implemented temporal query answering w.r.t. ontologies formulated in the Description Logic DL-Lite. Focusing on temporal conjunctive queries (TCQs), which combine conjunctive(More)
In modelling real-world knowledge, there often arises a need to represent and reason with meta-knowledge. To equip description logics (DLs) for dealing with such ontologies, we enrich DL concepts and roles with finite sets of attribute– value pairs, called annotations, and allow concept inclusions to express constraints on annotations. We show that this may(More)
Large-scale knowledge graphs (KGs) are widely used in industry and academia, and provide excellent use-cases for ontologies. We find, however, that popular ontology languages, such as OWL and Datalog, cannot express even the most basic relationships on the normalised data format of KGs. Existential rules are more powerful, but may make reasoning(More)