Catrina, thinking about this further, since ASK will terminate with
"true" once a match is found to the query, the following will let you
know whether or not a graph exists:
ASK
WHERE {
GRAPH ?GRAPH_VAR {?s ?p ?o}
}
...where ?GRAPH_VAR is pre-bound to the graph you are looking for. If
a match is found, ASK returns a "true", after finding the first triple
in the graph. If the graph does not exist (in a TBS workspace), ASK
returns a "false".
-- Scott
On Oct 12, 12:00 pm, Scott Henninger <[email protected]>
wrote:
> Catrina; What is the use case here? For finding whether there is any
> data in a graph, either of these examples will work. These are pretty
> core to Jena, so I'm not entirely sure how that would improve on
> either of these (?).
>
> -- Scott
>
> On Oct 12, 11:48 am, Catrina <[email protected]>
> wrote:
>
> > Yes, I thought of that too and I agree it would be more efficient.
> > But, I wondered about the cases where the Ontology might not be
> > defined. As you said in most cases it is defined. That's where I
> > thought my first query example could be handy. Maybe I'll look at
> > creating another custom sparqlmotion module and handle this in java
> > with jena.
>
> > Thanks
>
> > On Oct 12, 11:31 am, Scott Henninger <[email protected]>
> > wrote:
>
> > > Catrina; The second query, using smf:buildURI() to create a resource,
> > > should work. A NPE will occur when executing tops:definesStatements
> > > if the resource defined for ?baseURI does not exist in the model the
> > > query is applied to.
>
> > > Also, I note that your query is returning all triples for the graph,
> > > but you are only interested in whether or not a triple is defined for
> > > the graph. In that case, it will be more efficient to use a triple
> > > pattern. For example, in most cases the owl:Ontology is defined for a
> > > graph. So you could use:
>
> > > ASK
> > > WHERE
> > > { LET (?baseURI := smf:buildURI("http://someGraphUri";)) .
> > > ?baseURI a owl:Ontology .
>
> > > }
>
> > > …and only one triple will need to be found to for ASK to be true.
>
> > > -- Scott
>
> > > On Oct 12, 8:23 am, Catrina <[email protected]>
> > > wrote:
>
> > > > Is it possible to use <urn:var:GRAPH_VAR> in an ASK query? For
> > > > example, I want to dynamically determine if a graph exists with
> > > > something like the following where I previously set GRAPH_VAR.
> > > > ASK WHERE {
> > > > GRAPH <urn:var:GRAPH_VAR> {
> > > > } .
>
> > > > }
>
> > > > I tried something like the following, but I get a NullPointerException
> > > > if the graph does not exists.
> > > > ASK WHERE {
> > > > LET (?baseURI := smf:buildURI("http://someGraphUri";)) .
> > > > ?baseURI tops:definesStatements (?subject ?predicate ?object) .
>
> > > > }
>
> > > > Thanks,
> > > > Catrina- Hide quoted text -
>
> > > - Show quoted text -
--
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