Hi Elli!
[apparently your reply didn't come through the mailing list, but this
one should]
31.10.2012 23:11, Elli Schwarz kirjoitti:
Thank you for the tip. Yes, if I generate the index using the
larqbuilder command, I don't get the duplicates in the query, regardless
of the placement of the pf:testMatch line. (As an aside, why does the
default behavior of creating the index allow duplicates, but the default
of the larqbuilder command does not?)
Good to hear that eliminating duplicates works for you. I have no idea
why the defaults are as they are.
However, switching the order of where I place the pf:textMatch line
(while it may slow down the query), should not produce different
results, even if there are duplicates in the index. This would appear to
be a bug in how Larq applies the results of the index lookup to the query.
I'm not sure whether getting or not getting duplicates in specific
situations can be considered a bug. But yes, the implementation of LARQ
seems to be rather simplistic. It might help if the raw index results
were filtered to weed out duplicates before applying them to the query.
Then the choice whether to try to avoid duplicates during indexing would
only be an optimization issue.
BTW I'm not (so far) a LARQ developer, just a fellow user..
-Osma
Hi Elli!
It seems that at least part of your problem is having duplicates in the
LARQ index. Have you tried creating the Lucene index using the
larqbuilder command line tool, instead of removing the index and just
letting Fuseki rebuild it when it starts? See the end of my tutorial [1]
for a recipe.
As I understand it, unless you give larqbuilder the --allow-duplicates
option, it will try to avoid duplicates in the index. Though the index
building will take longer.
I've also noticed that it usually makes sense to place the pf:textMatch
pattern first in the query, otherwise it will be executed many times and
slow down the whole query, sometimes by a lot.
Hope this helps,
-Osma
[1] http://code.google.com/p/onki-light/wiki/InstallFusekiLARQ
On Tue, 23 Oct 2012, Elli Schwarz wrote:
> Hello,
>
>
> I am using Fuseki with Larq (thanks to Osma's recent instructions -
thanks Osma!) where I recompiled Jena (after adding the Larq
dependency) to Jena revision 1399877 (this past Friday morning's version
of the trunk). I'm noticing the following anomaly when querying the data:
>
> First I insert the following triples:
> prefix xsd: <http://www.w3.org/2001/XMLSchema#>
> insert data { graph <urn:test:foo> {
> <urn:test:s1> <urn:test:p1> "foo"^^xsd:string .
> <urn:test:s1> <urn:test:p2> "foo"^^xsd:string .
> <urn:test:s2> <urn:test:p3> "foo"^^xsd:string .
> } }
>
> Then I stop Fuseki, delete my index directory, and restart Fuseki.
(As an aside, I'd be very interested in a fix for this so I don't have
to restart Fuseki to rebuild the index - I'm watching JENA-164 and
hoping someone will be able to work on it soon!) Once Fuseki is back up,
I run the following query (I have default graph set as the union of
named graphs by default):
> PREFIX pf: <http://jena.hpl.hp.com/ARQ/property#>
> select * where {
> <urn:test:s1> ?p ?lit .
> ?lit pf:textMatch "foo" . }
>
> and I get 2 results as I expect:
>
> --------------------------------------------------------------------
> | p | lit |
> ====================================================================
> | <urn:test:p1> | "foo"^^<http://www.w3.org/2001/XMLSchema#string> |
> | <urn:test:p2> | "foo"^^<http://www.w3.org/2001/XMLSchema#string> |
> --------------------------------------------------------------------
> However, when I flip the order of my query like this:
>
> PREFIX pf: <http://jena.hpl.hp.com/ARQ/property#>
> select * where {
> ?lit pf:textMatch "foo" . <urn:test:s1> ?p ?lit .
> I get 6 results, instead of the two I expect:
>
> --------------------------------------------------------------------
> | lit | p |
> ====================================================================
> | "foo"^^<http://www.w3.org/2001/XMLSchema#string> | <urn:test:p1> |
> | "foo"^^<http://www.w3.org/2001/XMLSchema#string> | <urn:test:p2> |
> | "foo"^^<http://www.w3.org/2001/XMLSchema#string> | <urn:test:p1> |
> | "foo"^^<http://www.w3.org/2001/XMLSchema#string> | <urn:test:p2> |
> | "foo"^^<http://www.w3.org/2001/XMLSchema#string> | <urn:test:p1> |
> | "foo"^^<http://www.w3.org/2001/XMLSchema#string> | <urn:test:p2> |
>
--------------------------------------------------------------------My
guess as to what happens is that in the second query, first the query
executer executes the first line (the ?lit pf:textMatch "foo") and this
returns 3 results for foo, since there are 3 literals for "foo". Then,
the next line of the query has three bindings to ?lit, so it produces
the 6 results above (2 for each "foo" literal since there are 2
properties for <urn:test:s1>). I know that I can avoid this by using a
SELECT DISTINCT, but I still think the query shouldn't produce different
results based on switching the order. Additionally, if I put this in a
CONSTRUCT query, I can't use DISTINCT to eliminate the duplicate results
(unless I use a SELECT DISTINCT subquery which I'd rather avoid).
>
> Another point I've noticed is that in my other (much more complex)
queries, against a much larger dataset (~1.5 million triples), if I put
the pf:textMatch line anywhere but in the very beginning of the query,
the query takes a VERY long time to execute. If I put it as the first
line in the query, the query runs quickly. My guess for this is that the
query is executed in order, and it takes much more work for the query
executer to run the other parts of my query which contain many results,
and then have to go back and essentially filter out those results where
the literal doesn't match the pf:textMatch. I can always place the
pf:textMatch line first, but then I'm back to the problem mentioned
above where I get back too many duplicate results.
>
> Thank you very much for your help!
> -Elli
-- Osma Suominen | osma.suomi...@aalto.fi
<mailto:osma.suomi...@aalto.fi> | +358 40 5255 882
Aalto University, Department of Media Technology, Semantic Computing
Research Group
Room 2541, Otaniementie 17, Espoo, Finland; P.O. Box 15500, FI-00076
Aalto, Finland
--
Osma Suominen | osma.suomi...@aalto.fi | +358 40 5255 882
Aalto University, Department of Media Technology, Semantic Computing
Research Group
Room 2541, Otaniementie 17, Espoo, Finland; P.O. Box 15500, FI-00076
Aalto, Finland
