Date: 2012-07-13 13:56:47
From: jeni@jenitennison.com
Hi,
I have to delete all the data about particular resources in the triplestore, and I'm finding that it's taking an inordinately long time. I have tried separate queries like:
DELETE WHERE {
<http://example.org/x> ?p ?o .
}
;
DELETE WHERE {
<http://example.org/y> ?p ?o .
}
;
?
and I have tried a combined query like:
DELETE {
?s ?p ?o .
} WHERE {
?s ?p ?o .
FILTER (
?s = <http://example.org/x> ||
?s = <http://example.org/y> ||
...
)
}
Both of these seem to perform OK on my OWLIM-Lite instance but not on the OWLIM-SE instance. Could this difference between OWLIM-Lite performance and OWLIM-SE performance be down to a difference in the reasoning that's enabled (I have an empty ruleset on the OWLIM-Lite instance, but currently have the default owl-horst-optimized' on the OWLIM-SE instance)?
Is there an alternative method of deleting all the data about a particular resource that I should use?
Thanks,
Jeni

asked 03 Apr '13, 10:34

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Date: 2012-07-13 19:07:12
From: barry.bishop@ontotext.com
Hi Jeni,
Another issue! Thanks for reporting it. Deleting statements is a bit 
more involved than simply  querying them, so there are several 
possibilities for what might be causing your problem. I'll let the 
developers comment on this first though.
By the way, there is something fundamentally different about OWLIM-Lite 
and OWLIM-SE in this regard:
In OWLIM-Lite, deleting even a single statement triggers the 
recomputation of all inferred statements, because there is no truth 
maintenance mechanism. In your case, you have inference turned off, so 
you won't see any problem. However, if you load a lot of statements in 
to OWLIM-Lite using the owl-max rule-set, you will find deleting 
statements is not so fast.
In OWLIM-SE, which scales to billions of statements, recomputing the 
whole inferred closure every time any statement is deleted is not 
practical. Therefore it uses a completely different mechanism that we 
sometimes call 'smooth delete'. There is still no truth maintenance 
information stored, but what happens is that some forward/backward 
chaining cycles are done to determine which inferences should be deleted 
whenever some explicit statements are retracted. This took a little 
while to get right, but it has proven to be very performant. It is 
possible that you could have uncovered a problem with this mechanism, or 
it could be that the poor delete performance has its cause elsewhere.
Again, I'll wait for the developers to comment on this, but one of us 
will get back to you very soon.
Have a great weekend,
barry
Barry Bishop
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answered 03 Apr '13, 10:34

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Asked: 03 Apr '13, 10:34

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