(I had forgotten to create a new thread and ended up re-hijacking this
one. So I'm starting a new thread here... Please in the future, don't
use Reply to start a new thread.)
Kevin, a simple solution is to use the following aggregate:
SELECT ?person1 ?person2 count(?forum)
WHERE
{ ?person1 sioc:follows ?forum .
?person2 sioc:follows ?forum .
FILTER (?person1 != ?person2) .
} GROUP BY ?person1 ?person2
Of course, this will get the results twice, once for person1 and again
for person2. But this is the nature of any pairwise comparison with
SPARQL.
-- Scott
On 5/14/10 1:12 PM, Kevin wrote:
> Scott,
>
> Thanks again. The simple scenario you've outlined I understand. What I
> was going for is:
>
> Show me a list of users who have more than 1 forum they follow in
> common.
> If I get that, then how many forums do they share in common (count)
>
> Kevin
>
> On May 14, 10:29 am, Scott Henninger <[email protected]>
> wrote:
>> Kevin; Unless you need to use aggregate in your query, sub-selects are
>> rarely needed. The key to understanding SPARQL is that it is a mirror of
>> RDF. Each triple represents an edge in a graph. Using variables creates a
>> graph pattern that is matched against the RDF graph.
>> If what you want are the people following the same forum, you can visualize
>> this as a forum as the central node of a graph and finding all people
>> following that forum. Then filter out all cases where it's the same person.
>> SELECT ?person1 ?forum ?person2
>> WHERE
>> { ?person1 sioc:follows ?forum .
>> ?person2 sioc:follows ?forum .
>> FILTER (?person1 != ?person2) .
>> }
>> To get a count of the number of people following a forum use the count
>> aggregate, grouping by the forum matches:
>> SELECT ?forum count(*)
>> WHERE
>> { ?person1 sioc:follows ?forum .
>> ?person2 sioc:follows ?forum .
>> FILTER (?person1 != ?person2) .
>> } GROUP BY ?forum
>> -- Scott
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