Implementing Controlled Query Evaluation in OBDA

In the Ontology Based Data Access (OBDA) framework, users access a relational data source by querying a domain ontology, whose classes and properties are connected to the data via declarative mappings. OBDA is adopted for data management in various sectors, notably healthcare, where confidentiality of information is a key concern that requires data to be properly protected from unauthorized accesses. Controlled Query Evaluation (CQE) is a framework for privacy-preserving query answering in the presence of an ontology. In CQE, policies are used to represent the information that should be kept confidential, and the aim is to devise from policy specifications suitable censors that enforce data protection. Therefore, it is desirable to integrate CQE in OBDA to obtain a robust privacy-aware data management framework. This has been done in the recently proposed Policy-Protected OBDA (PPOBDA) framework, which ensures the integration of CQE within OBDA by embedding policies into mappings. In this paper, we present an open-source solution that implements PPOBDA and a simplified algorithm for policy embedding, compared to previously proposed ones. This facilitates the adoption of PPOBDA using any OBDA query engine capable of translating SPARQL queries into SQL. In our implementation, we rely on Ontop, a state-of-the-art open-source OBDA tool.