I am working on a collaborative-filtering recommender system. I built such a system before in a parallel-threaded environment, querying RDF with SPARQL. This worked well, because of the parallel nature of SPARQL and RDF graphs. However, I am now working in a standard desktop PC, and am wondering if using SPARQL is still the way to go in a largely serial environment. I've looked at dotNetRDF, as I'm using C#, and am wondering if it is any more efficient than simple SQL, especially now that dotNetRDF seems to be moving away from a SQL back-end.
So as far as performance on a few threads go, SQL or dotNetRDF? Tables or graphs?