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From Paolo Castagna <>
Subject On SELECT DISTINCT ?g WHERE { GRAPH ?g { ?s ?p ?o } } ...
Date Sat, 10 Mar 2012 12:57:38 GMT
this is one of those queries people want to do: SELECT DISTINCT ?g WHERE { GRAPH ?g { ?s ?p
?o } } (see recent thread on jena-users).
It isn't unreasonable: people want to know what are the graphs in an RDF dataset, but as for
SELECT DISTINCT ?p WHERE {?s ?p ?o.} or SELECT DISTINCT ?cls WEHRE {?i a ?cls.}, I do not
see what we could
possibly do to speed things up. It's a scan of the entire index and therefore expensive, even
more so if the index do not fit into RAM.

However, if there was an easy way to see all the triples/quads added/removed, those would
be very easy to compute and fast to return... however, one need to spot the query and have
the optimizer use a
different index for those queries. I also imagine that once you start going doing this path,
more and more 'useful' queries will appear => more and more indexes => more and more
slowdown at write time.


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