Do you already have a movie database in RDF (with statements like so-and-so directed such-and-such movie) or do you have to make one?

I have done RDF similarity queries with queries similar to

   select ?s2 (count(?s1) as ?cnt) {
       ?s1 ?p ?o .
       ?s2 ?p ?o .
   } group by ?p ?o

where ?s1 is bound to the input movie. That will count the number of shared attributes such as director, actor, year, tagged genre, etc. you can do better if you weight it so po’s that are less common contribute more to the score. Against dbpedia that heuristic does very well for most subjects.