Ontology-based Data Access: From Theory to Practice
Ontology-based data access (OBDA) has become a popular paradigm for accessing data stored in legacy sources using Semantic Web technologies. In OBDA, users access the data through a conceptual layer, which provides a convenient query vocabulary abstracting from specific aspects related to the data sources. This conceptual layer is typically expressed as an RDF(S) or OWL ontology, and it is connected to the underlying relational databases using R2RML mappings. When the ontology is queried in SPARQL, the OBDA system exploits the mappings to retrieve elements from the data sources and construct the answers expected by the user. Different approaches for query processing in OBDA have been proposed. We focus here on the virtual approach, which avoids materializing triples retrieved through mappings and answers the SPARQL queries by translating them into SQL queries over the database. In this tutorial we will give the audience a gentle introduction to OBDA covering both practical and theoretical aspects. One the practical side, we will illustrate novel challenges for OBDA arising in two large-scale industrial use cases studied in the European project Optique. We will show how to overcome these challenges through efficient translations from SPARQL to SQL, considering mappings, ontologies, and rules. On the theoretical side, we will present recent theoretical development underlying these techniques.
- Introduction to Ontology-based Data Access
- Scalable SPARQL Query Answering in OBDA
- Reconciling SPARQL and SQL Semantics
- Hands on Session
- Building Ontologies and Mappings using Protege.
- Setting up a SPARQL end-point.
- Ontology-based data integration.
- basic knowledge in relational databases, RDF, and SPARQL;
- background in description logics is preferable, but not strictly necessary.