On 22/08/15 06:37, Nauman Ramzan wrote:
Hi Mark
Did you connect virtuoso with fuseki or you just import data into fuseki ?
On Aug 22, 2015, at 2:56 AM, Mark Feblowitz <[email protected]> wrote:
This seems like it should be a FAQ, but I’m not finding anything useful.
I’m using SPARQL to explore linked data, which includes discovering predicates.
My understanding was that I could bind a subject and use variables for
predicate and object.
It’s important to note that what I’m experiencing is when using dbpedia, which
is built on Virtuoso - perhaps my question should be posted elsewhere? But I am
doing this via a Fuseki endpoint, so there’s at least some relevance :-?
Yes - this is possible see below.
Fuseki is just passing on the query and is not responsible for the
results. "common carrier" :-)
Here’s what I’m trying to do:
I have some queries to a Fuseki endpoint that call out to dbpedia using SERVICE
blocks. Before entering the service I bind a value for ?Player, and then with
the service I pose the query;
PREFIX do: <http://dbpedia.org/ontology/>
...
{SELECT DISTINCT * where {
?Player a do:BasketballPlayer.
?Player ?r ?A.
?Player2 ?r ?A }
Mark - did you test just
SELECT DISTINCT * where {
?Player a do:BasketballPlayer.
?Player ?r ?A.
?Player2 ?r ?A }
in isolation (SERVICE call?) or as a nested SELECT in a larger query?
It is possible, especially in the sub-query form, that the query plan is
expensive because property variables are uncommon (but correct) so less
work goes on into optimizing such plans.
Also an internal timeout executing that part of the query would explain
what you are seeing.
There are going to be a lot of answers - 14,818,205,957? - counting
non-DISTINCT. The DISTINCT version may be significantly more expensive
but
SELECT (count(DISTINCT *) AS ?c) {
is a syntax error for DBpedia though it is legal SPARQL.
Andy
I expected to find a binding for ?r as do:team. And when I pre-bind ?r to that,
I see plenty of bindings for ?A and ?Player2. The one binding that I do see
when leaving ?r unbound is
http://www.w3.org/1999/02/22-rdf-syntax-ns#type
(I notice that dbpedia virtuso is limited - it cannot handle a BIND statement.)
Is the case am I seeing universal behavior or behavior specific to virtuoso?
Either way, are there clever workarounds?
I do know that I can “white-list in” some bindings for ?r, using a VALUES
statement. But that pretty much defeats the discovery purpose. Also, as this is
varied and often schema-less content, I can’t rely on an ontology as a guide to
defined predicates.
Any suggestions?
Thanks,
Mark
