Hi Jindřich,
On 24-Nov-14 10:23 AM, Jindřich Mynarz wrote:
Hi,
every Virtuoso SPARQL endpoint now includes a checkbox called "Strict
checking of void variables". Unfortunately, I haven't been able to
find documentation describing what exactly this checkbox (or debug=on
GET parameter) does. Can you please point me to its authoritative
description?
My motivation: As others in the past (e.g.,
http://boards.openlinksw.com/support/viewtopic.php?f=12&t=1381) I have
on numerous occasions encountered the "Virtuoso 37000 Error SP031:
SPARQL compiler: Variable '_::trans_subj_XYZ is used in subexpressions
of the query but not assigned" error when using SPARQL 1.1 property
paths. With "Strict checking of void variables" turned off, this error
goes away. I'd like to know what exactly is changed.
When "Strict checking of void variables" is checked, this means the
SPARQL Compiler will check if all variables are declared,
and if there are some of the variables that are not declared, an error
will be raised.
For instance ( live link with checked "Strict checking of void
variables" -- http://bit.ly/1zRdfnk):
select ?y
where
{
?s ?p ?o
}
will raise an error:
Virtuoso 37000 Error SP031: SPARQL compiler: Variable 'y' is used in the
query result set but not assigned
which is correct since ?y is not declared in the WHERE clause.
As for the queries in
http://boards.openlinksw.com/support/viewtopic.php?f=12&t=1381 I have
being able to reproduce the issue with this one:
|define sql:signal-void-variables 1
SELECT DISTINCT ?s ?p ?v ?c ?g
FROM <http://our_namespace/plugins/>
FROM <http://our_namespace/something/>
WHERE
{
{
?s ?p ?v .
OPTIONAL { ?v
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type> ?c } .
OPTIONAL { GRAPH ?g { ?s
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type> ?v } }
} .
{ SELECT ?s
WHERE { <http://localhost:8000/11>
<http://our_namespace/something_different/> ?s }
}
}
Live link: -- http://bit.ly/1HD3kXB
Here the last "SELECT" is redundant and can be replaced with plain triple,
i.e. if I change:
|
|{ SELECT ?s
WHERE { <http://localhost:8000/11>
<http://our_namespace/something_different/> ?s }
}
to :
|
|{ ?s ?p ?v .
<http://localhost:8000/11>
<http://our_namespace/something_different/> ?s .
}|
then I get no error -- live link: http://bit.ly/1zRfCGJ
I hope this helped.
Best Regards,
Rumi Kocis
Best,
Jindřich
--
Jindřich Mynarz
http://mynarz.net/#jindrich
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