Find out the missing properties resources - sparql

Question

I am very new to this semantic web and I am doing some experiments with Sparql & DBPEDIA. I wrote a query to find out all the records which has firstName(givenName) and lastName(surName).
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
select count(DISTINCT ?x) where {
?x foaf:givenName ?y;
foaf:surname ?z.
}
When I run this query I got 9,80,000 records. But when I ran the individual queries (for firstName and lastName) I got 9,92,000 records for firstName and 9,80,000 for lastName.
Here my question is how can I get the resources which has only firstName but not the lastName...???

Answer 1

You can use the NOT EXISTS clause with a FILTER to achieve this:
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT (COUNT(DISTINCT ?x) AS ?count)
WHERE
{
?x foaf:givenName ?y .
FILTER(NOT EXISTS { ?x foaf:surname ?z. })
}
This filters out matches for ?x where the NOT EXISTS pattern is also matched.
Alternatively you can use the MINUS clause which does roughly the same bar some minor differences which won't affect your query:
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT (COUNT(DISTINCT ?x) AS ?count)
WHERE
{
?x foaf:givenName ?y .
MINUS { ?x foaf:surname ?z. }
}