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

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