Sparql - Applying limiting criteria to predicates - sparql

Question

I'm fairly new to RDF / Sparql, so apologies for any incorrect terminology, and also for the fairly terrible example that follows:
Given the following RDF dataset:
#prefix owl: <http://www.w3.org/2002/07/owl#> .
#prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
#prefix e: <http://www.example.com/#> .
#prefix foaf: <http://xmlns.com/foaf/0.1/> .
e:Freemason a owl:Class .
e:Civilian a owl:Class .
e:Marty a e:Freemason .
e:Eugene a e:Freemason .
e:Mike a e:Freemason .
e:Alan a e:Freemason .
e:Paul a e:Civilian .
e:Marty foaf:knows e:Eugene .
e:Eugene foaf:knows e:Mike .
e:Eugene foaf:knows e:Paul .
e:Paul foaf:knows e:Alan .
I'm trying to identify friends-of-friends that e:Marty knows through other e:Freemasons only.
So:
Marty knows Mike through Eugene, and they're all Freemason's so it's fine
Marty knows Eugene, who has a Civilian friend Paul. Paul has a Freemason friend Alan. However, Marty doesn't have a "freemason only" path to Alan, so he should be excluded.
Here's the SPARQL query I have:
prefix e: <http://www.example.com/#>
prefix foaf: <http://xmlns.com/foaf/0.1/>
SELECT *
{
<http://www.example.com/#Marty> foaf:knows+ ?target .
?target a e:Freemason .
}
This returns:
http://www.example.com/#Eugene
http://www.example.com/#Mike
http://www.example.com/#Alan
Here, Alan is included as he matches the is-a-freemason criteria.
How I do modify the query to exclude Alan?

Answer 1

I don't know the solution in pure SPARQL, sorry.
In OpenLink Virtuoso's SPARQL-BI, the solution is this query
prefix e: <http://www.example.com/#>
prefix foaf: <http://xmlns.com/foaf/0.1/>
select *
where
{
{ select ?orig ?target
where
{ ?orig foaf:knows ?target .
?target a e:Freemason .
}
}
option ( TRANSITIVE,
T_IN(?orig),
T_OUT(?target),
T_DISTINCT,
T_MIN(1)
)
filter ( ?orig = <http://www.example.com/#Marty> )
}
-- with these results --
orig target
<http://www.example.com/#Marty> <http://www.example.com/#Eugene>
<http://www.example.com/#Marty> <http://www.example.com/#Mike>

Answer 2

Here's an example using SPARQL that has been deprecated from the spec (for reasons I never understood) but remains supported in Virtuoso (which will be the case for the unforeseeable future)
## RDF-Turtle Start ##
#prefix owl: <http://www.w3.org/2002/07/owl#> .
#prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
#prefix e: <http://www.example.com/#> .
#prefix foaf: <http://xmlns.com/foaf/0.1/> .
e:Freemason a owl:Class .
e:Civilian a owl:Class .
e:Marty a e:Freemason .
e:Eugene a e:Freemason .
e:Mike a e:Freemason .
e:Alan a e:Freemason .
e:Paul a e:Civilian .
e:Marty foaf:knows e:Eugene .
e:Eugene foaf:knows e:Mike .
e:Eugene foaf:knows e:Paul .
e:Paul foaf:knows e:Alan .
## RDF-Turtle End ##
Using Property Path Pattern from SPARQL that has been deprecated
but preserved in Virtuoso
PREFIX e: <http://kingsley.idehen.net/DAV/home/kidehen/Public/Linked%20Data%20Documents/Tutorials/club-member-test.ttl#>
PREFIX dsn: <http://kingsley.idehen.net/DAV/home/kidehen/Public/Linked%20Data%20Documents/Tutorials/club-member-test.>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT *
FROM dsn:ttl
WHERE {
e:Marty foaf:knows{2} ?target .
?target a e:Freemason .
}
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