Ensuring License Compliance in Federated Query Processing

National audience; When two or more licensed datasets participate in the evaluation of a federated query, the query result must be protected by a license that is compliant with each license of the involved datasets. However, such a license does not always exist, and this leads to a query result that cannot be reused. We propose to deal with this issue during the federated query processing by discarding datasets of conflicting licenses. But then, a query with an empty result set can be obtained. To face this problem, we use query relaxation techniques. Our problem statement is, given a SPARQL query and a federation of licensed datasets, how to guarantee a relevant and non-empty query result whose license is compliant with each license of involved datasets? In a distributed environment, the challenge is to limit communication costs when the query relaxation process is necessary. In this paper, to detect and prevent license conflicts, we propose FLiQuE, a license aware query processing strategy for federated query engines. Experiments show that FLiQuE guarantees license compliance, and if necessary, can find relevant relaxed federated queries with a limited overhead in terms of execution time.