Query hangs, a very long time

[Mark Feblowitz]

This is a fragment of an even larger query that might never complete in our 
lifetimes:

SELECT DISTINCT ?O ?T  ?E
WHERE{  
?E a x:E. 
        { SELECT ?O ?T 
                  WHERE {
                        ?O :oE ?;
                                :oT ?T .
                        } ORDER BY DESC(?T) 
                          LIMIT 3
                }
        }

Here’s what I want:

For every E, the top 3 O’s as sorted by T.

My TDB store contains 779 O’s, 7273 E’s, and a T for every O.

The full query is this:

SELECT DISTINCT ?O ?T ?S ?E ?P
WHERE{  
                ?E a prov:E. 
                { SELECT ?O ?T 
                  WHERE {
                        ?O :otE ?E;
                                :oT ?T .
                        } ORDER BY DESC(?T) 
                          LIMIT 3
                }{ SELECT ?SH
                  WHERE {
                  ?EHS :ehsO ?O. 
                  ?EH :ehEHSf ?EHS. 
                  ?SHS :shsEHS ?EHS; 
                        :shsSH ?SH .
                  ?SH :rank ?SHRank.
                  } ORDER BY ASC(?SHRank)
                    LIMIT 1 
                } 
                ?SH :shS ?S.
        OPTIONAL {?O :op ?P.}
        }

A pretty complex query, and one that *certainly* won’t complete if the simpler 
one won’t.

Thanks,

Mark