Relational to RDF Data Migration by Query Co-Evaluation

Abstract: In this paper we define a new algorithm to convert an input relational database to an output set of RDF triples. The algorithm can be used to e.g. load CSV data into a financial OWL ontology such as FIBO. The algorithm takes as input a set of relational conjunctive (select-from-where) queries, one for each input table, from the three column (subject, predicate, object) output RDF schema to the input table's relational schema. The algorithm's output is the only set of RDF triples for which a unique round-trip of the input data under the relational queries exists. The output may contain blank nodes, is unique up to unique isomorphism, and can be obtained using elementary formal methods (equational theorem proving and term model construction specifically). We also describe how (generalized) homomorphisms between graphs can be used to write such relational conjunctive (select-from-where) queries, which, due to the lack of structure in the three-column RDF schema, tend to be large in practice. We demonstrate examples of both the algorithm and mapping language on the FIBO financial ontology.