Not understanding UNION well, or something

[Bob DuCharme]

I'm trying to expand the query shown at 
http://www.snee.com/bobdc.blog/2008/11/sparql-at-the-movies.html#id203668 
to include the director and movie names in the result of the query sent 
to http://data.linkedmdb.org/sparql. I guess my main problem is trying 
to understand how I can set it up so that ?actor is bound to the same 
value throughout the query but ?movie and ?movieName can be bound to 
different values in the two patterns. I know that one actor was in a 
single movie by each of the two directors named below, and while the 
following doesn't give me an error when submitted it gives an unrelated 
set of data. I may be going about it completely wrong.

Any suggestions?

thanks,

Bob

####################

SELECT ?actorName ?dirName ?movieName WHERE {

 ?dir1 <http://data.linkedmdb.org/resource/movie/director_name> "John 
Waters".
 ?dir2 <http://data.linkedmdb.org/resource/movie/director_name> "Steven 
Spielberg".

 ?actor  <http://data.linkedmdb.org/resource/movie/actor_name> ?actorName.

  {
    ?movie <http://data.linkedmdb.org/resource/movie/director> ?dir1;
           <http://data.linkedmdb.org/resource/movie/actor> ?actor;
           <http://purl.org/dc/terms/title> ?movieName.
    ?dir1 <http://data.linkedmdb.org/resource/movie/director_name> 
?dirName.
  }

  UNION

  {
    ?movie <http://data.linkedmdb.org/resource/movie/director> ?dir2;
           <http://data.linkedmdb.org/resource/movie/actor> ?actor;
           <http://purl.org/dc/terms/title> ?movieName.
    ?dir2 <http://data.linkedmdb.org/resource/movie/director_name> 
?dirName.
  }
}