On 10/03/12 12:57, Paolo Castagna wrote:
Hi, 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.
Paolo
Isn't that a good usecase for query caching?
There is a need for a graph management facility, and an effect of that
could be to have GRAPH ?g {} (or anything optimzied to the same) go look
in the graph info datastructures.
But query caching has so many other advantages, seems a shame not to us it.
Andy
