Efficiently Pinpointing SPARQL Query Containments

Query containment is a fundamental problem in database research, which is relevant for many tasks such as query optimisation, view maintenance and query rewriting. For example, recent SPARQL engines built on Big Data frameworks that precompute solutions to frequently requested query patterns, are conceptually an application of query containment. We present an approach for solving the query containment problem for SPARQL queries - the W3C standard query language for RDF datasets. Solving the query containment problem can be reduced to the problem of deciding whether a sub graph isomorphism exists between the normalized algebra expressions of two queries. Several state-of-the-art methods are limited to matching two queries only, as well as only giving a boolean answer to whether a containment relation holds. In contrast, our approach is fit for view selection use cases, and thus capable of efficiently enumerating all containment mappings among a set of queries. Furthermore, it provides the information about how two queries' algebra expression trees correspond under containment mappings. All of our source code and experimental results are openly available.