Relaxing and Restraining Queries for OBDA
This work addresses query flexibility in OBDA for users dealing with unstructured and incomplete data, but it is incremental as it builds on existing OBDA frameworks.
The paper tackles the problem of modifying queries in ontology-based data access (OBDA) by relaxing or restraining them to retrieve more or fewer answers, and it shows that conjunctive queries over an extended DL-Lite ontology with complex role inclusions are first-order rewritable.
In ontology-based data access (OBDA), ontologies have been successfully employed for querying possibly unstructured and incomplete data. In this paper, we advocate using ontologies not only to formulate queries and compute their answers, but also for modifying queries by relaxing or restraining them, so that they can retrieve either more or less answers over a given dataset. Towards this goal, we first illustrate that some domain knowledge that could be naturally leveraged in OBDA can be expressed using complex role inclusions (CRI). Queries over ontologies with CRI are not first-order (FO) rewritable in general. We propose an extension of DL-Lite with CRI, and show that conjunctive queries over ontologies in this extension are FO rewritable. Our main contribution is a set of rules to relax and restrain conjunctive queries (CQs). Firstly, we define rules that use the ontology to produce CQs that are relaxations/restrictions over any dataset. Secondly, we introduce a set of data-driven rules, that leverage patterns in the current dataset, to obtain more fine-grained relaxations and restrictions.