Title : Reasoning with Description Logics Ontologies and Knowledge Graphs

Presenter David Carral
Abstract Ontology-based access to knowledge graphs (KGs) has recently gained a lot of attention. One of the research challenges when accessing these large data structures is to enable "the capability of combining diverse reasoning methods and knowledge representations while guaranteeing the required scalability, according to the reasoning task at hand." [1] In our work, we address this challenge with a focus on reasoning with KGs extended with Description Logics (DL) ontologies. In principle, one could make use of existing DL reasoners to solve these reasoning tasks. However, DL reasoners---which are designed to deal with complex terminological axioms---do not scale well in the presence of large amounts of assertional information. In contrast, existing rule engines such as VLog or RDFOx can efficiently reason with data-intensive knowledge bases. To take advantage of these powerful implementations, we propose several data-independent mappings from DL TBoxes into rule sets that preserve the outcomes of conjunctive query (CQ) answering. Our experiments indicate that reasoning with rule engines over the resulting CQ-preserving rewritings can be significantly more efficient than using state-of-the-art DL reasoners over the original DL ontologies. [1] This quote is taken from the description of a recent Daghstul seminar on "Knowledge Graphs: New Directions for Knowledge Representation on the Semantic Web" (https://www.dagstuhl.de/en/program/calendar/semhp/?semnr=18371)

Title : "Fuzzy Semantic Labeling of Semi-structured Numerical Datasets

Presenter Ahmad Alobaid
Abstract SPARQL endpoints provide access to rich sources of data (e.g. knowledge graphs), which can be used to classify other less struc- tured datasets (e.g. CSV files or HTML tables on the Web). We propose an approach to suggest types for the numerical columns of a collection of input files available as CSVs. Our approach is based on the application of the fuzzy c-means clustering technique to numerical data in the input files, using existing SPARQL endpoints to generate training datasets. Our approach has three major advantages: it works directly with live knowledge graphs, it does not require knowledge-graph profiling before- hand, and it avoids tedious and costly manual training to match val- ues with types. We evaluate our approach against manually annotated datasets. The results show that the proposed approach classifies most of the types correctly for our test sets.