> On 01 Feb 2016, at 13:49, Andy Seaborne <[email protected]> wrote: > > On 01/02/16 12:11, Joël Kuiper wrote: >> Hey all, >> >> I’m trying to run a query to find the path to the root concept of a graph. >> The entries are defined as rdfs:subClassOf >> >> Currently I’m using >> >> PREFIX skos: <http://www.w3.org/2004/02/skos/core# >> <http://www.w3.org/2004/02/skos/core#>> >> PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema# >> <http://www.w3.org/2000/01/rdf-schema#>> >> PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns# >> <http://www.w3.org/1999/02/22-rdf-syntax-ns#>> >> >> SELECT ?parent ?label >> WHERE { >> GRAPH ?g { >> ?concept rdfs:subClassOf* ?parent >> }} >> >> However on a moderately sized data set < 1M triples, this query sometimes >> takes /minutes/. >> I suspect it has to do with the disk-based TDB (since I hear my HDD spin a >> lot), but still. >> Is there a way to optimise this query, maybe by using a different reasoner? >> And if so how would that reasoner be used! >> >> Thanks in advance, >> >> Joël >> > > If you are using a reasoner and doing rdfs:subClassOf* then that is doing > excessive redundant work. > > (Otherwise, with TDB is materialises more nodes that it needs to.) > > The root is a node without a parent so this might help, without a reasoner: > > PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> > > SELECT ?top > WHERE { > GRAPH ?g { > ?concept rdfs:subClassOf ?top > FILTER NOT EXISTS { ?top rdfs:subClassOf ?x } > } > } >
I wasn’t using a reasoner yet (it’s just the bare Fuseki TDB assembler file). If I understand correctly your query does not allow the path of all the intermediate nodes to be found? E.g. A subclassOf B subclassOf C ….? Thanks :-)
