SPARQL query with/without asterisk

[timmy....@gmail.com]

Hi,

Please check the following SPARQL query:

PREFIX : <http://prefix#>
SELECT (count(distinct ?subject) as ?amount)
WHERE {
  ?subject rdf:type :Patient .
  ?subject :has_gender ?gender .
  ?gender rdf:type :MALE .
}

This query returns 0 while in my humble opinion it should not. ?gender is of type "http://prefix#MALE" as verified by the query below. This query does return the correct amount of patients.

PREFIX : <http://prefix#>
SELECT (count(distinct ?subject) as ?amount)
WHERE {
  ?subject rdf:type :Patient .
  ?subject :has_gender ?gender .
  FILTER (str(?gender) = "http://prefix#MALE")
}

The only way I can get my original query to work, is by adding an asterisk after rdf:type. Why is this necessary? Thanks!

[Héctor Pérez-Urbina]

Hello,

Can you send us the ontology you're querying?

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Best,
Héctor

[Timmy Storms]

Hi Héctor,

Actually, all triples are derived from an odba file, as we were testing ontop previously. We also have an ontology in place, but it is not needed for this basic query.

Don't you agree that the query should work? Is there some more info you'd require?

Thanks,

Timmy

[Héctor Pérez-Urbina]

Timmy,

Since the second query is giving you some results, I assume your data is of the form

:a1 a :Patient ;

:has_gender :MALE .

Therefore, the query binds ?gender to :MALE.

Your first query, however, assumes that the underlying data is of the form

:m a :MALE .

:a1 a :Patient ;

:has_gender :m .

That is, the query is trying to bind ?gender to something that is of type :MALE, which explains the empty results. 

By the way, given the usual semantics of gender, I would suggest to do something like

:a1 a :Patient, :Male .

and use the query

PREFIX : <http://prefix#>
SELECT (count(distinct ?subject) as ?amount)
WHERE {

  ?subject a :Patient, :Male .
}