Testing the presence of a predicate in SPARQL

Question

I have the following RDF model:

@prefix : <http://test.com/#> .

:graph1   :hasNode   :node1 ;
          :centerNode   :node1 .

:graph1   :hasNode   :node2 .
:graph1   :hasNode   :node3 .

I want to run a SPARQL query in which if a :nodeX is related to a :graphX with a predicate :centerNode I return true (or some other indication) otherwise false; The result would look something like the following:

?n       ?g        ?centered
-----------------------------
:node1   :graph1   true
:node2   :graph1   false
:node3   :graph1   false

Is there a way to do this in SPARQL 1.0? if not, can it be done with in SPARQL 1.1?

Answer 1

You can combine EXISTS and BIND as follows in SPARQL 1.1:

PREFIX : <http://test.com/#>

SELECT * WHERE { 
  ?graph :hasNode ?node .
  BIND( EXISTS { ?graph :centerNode ?node } as ?isCentered )
}

Using Jena's ARQ, I get these results:

$ /usr/local/lib/apache-jena-2.10.0/bin/arq \
   --data predicate.n3 \
   --query predicate.sparql
---------------------------------
| graph   | node   | isCentered |
=================================
| :graph1 | :node3 | false      |
| :graph1 | :node2 | false      |
| :graph1 | :node1 | true       |
---------------------------------

Answer 2

In SPARQL 1.0,

SELECT * { 
  ?graph :hasNode ?node .
  OPTIONAL{ ?graph :centerNode ?node1 FILTER sameterm(?node, ?node1) }
}

and ?node1 will be bound or not bound in the answers. Cardinality is messy though.

OPTIONAL/!BOUND can do a sort of NOT EXISTS:

SELECT * { 
  ?graph :hasNode ?node .
  OPTIONAL{ ?graph :centerNode ?node1 FILTER sameterm(?node, ?node1) }
  FILTER( !bound(?node1) )
}

Answer 3

That's exactly the purpose of ASK queries in SPARQL:

PREFIX : <http://test.com/#>
ASK WHERE { 
  ?graph :hasNode ?node .
  ?graph :centerNode ?node .
}