On 5/5/11 7:12 PM, Curran Kelleher wrote:
Greetings,
I noticed a discrepancy between my expectations and the results I get
from a few SPARQL queries on DBPedia:
Querying DBPedia for a listing of all television stations returns no
results:
|SELECT ?x
WHERE {
{ ?x rdf:type<http://dbpedia.org/class/yago/TelevisionStation104406350> }
}|
However if I specify to include instances of subclasses one
inheritance level down, results do appear:
|SELECT ?station ?subclass
WHERE {
?station rdf:type ?subclass.
?subclass
rdfs:subClassOf<http://dbpedia.org/class/yago/TelevisionStation104406350>
} LIMIT 100|
I expected the first query to return the results of the second (with
additionally all the transitive subclasses), and I just wanted to ask
on this list, is this an incorrect expectation?
Translation: I assumed reasoning with full transitive closure is on by
default.
When an endpoint is exposed to the InterWeb for anyone to use, that mode
is impractical and self fulfilling re. deliberate or inadvertent DOS.
Thus, we make reasoning optional via inference rules and sparql pragmas.
Shouldn't the query engine automatically infer that instances of
subclasses are also instances of superclasses and include those in the
result?
See comments above.
I thought this kind of useful inferencing was one thing that gave
SPARQL it's shine!
Yes! And if its smart then even better :-)
I have pointed out this issue in this blog post
<http://curransoft.com/code/2011/05/querying-dbpedia-for-tv-stations/>. Thanks
for your time!
Please update your post bearing in mind my explanation and links proving
my point below:
Links:
1.
http://virtuoso.openlinksw.com/presentations/SPARQL_Tutorials/SPARQL_Tutorials_Part_2/SPARQL_Tutorials_Part_2.html#(46)
-- Virtuoso Inference Rules Tutorial
2.
http://lod.openlinksw.com/describe/?uri=http%3A%2F%2Fdbpedia.org%2Fclass%2Fyago%2FTelevisionStation104406350
-- No Inference Context (no rule selected) so only 5 pages
3.
http://lod.openlinksw.com/describe/?uri=http%3A%2F%2Fdbpedia.org%2Fclass%2Fyago%2FTelevisionStation104406350&inf=http%3A%2F%2Fdbpedia.org%2Fresource%2Finference%2Frules%2Fyago%23
-- Inference Context on (rule selected via Settings Tab which has
drop-down for rules selection) so 49 pages
4.
http://dbpedia.org/describe/?uri=http%3A%2F%2Fdbpedia.org%2Fclass%2Fyago%2FTelevisionStation104406350&inf=http%3A%2F%2Fdbpedia.org%2Fresource%2Finference%2Frules%2Fyago%23
-- DBpedia example with Inference
5.
http://dbpedia.org/describe/?uri=http%3A%2F%2Fdbpedia.org%2Fclass%2Fyago%2FTelevisionStation104406350
DBpedia example with Inference Off.
Kingsley
Best regards,
Curran Kelleher
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--
Regards,
Kingsley Idehen
President& CEO
OpenLink Software
Web: http://www.openlinksw.com
Weblog: http://www.openlinksw.com/blog/~kidehen
Twitter/Identi.ca: kidehen
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