Hi,
despite using SPARQL for years, cases where different implementations
return different results leave me scratching my head. Can someone help
me out with this?
I have a rather simple query:
PREFIX schema: <https://schema.org/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX sioc: <http://rdfs.org/sioc/ns#>
SELECT * WHERE {
GRAPH ?docGraph {
?doc sioc:has_container <https://localhost:4443/employees/>;
foaf:primaryTopic ?employee.
OPTIONAL { ?employee schema:sponsor ?reportsToEmployee. }
}
}
ORDER BY ?doc
Dydra returns 9 results:
employee,reportsToEmployee
https://localhost:4443/employees/1/#this,https://localhost:4443/employees/2/#this
https://localhost:4443/employees/2/#this,
https://localhost:4443/employees/3/#this,https://localhost:4443/employees/2/#this
https://localhost:4443/employees/4/#this,https://localhost:4443/employees/2/#this
https://localhost:4443/employees/5/#this,https://localhost:4443/employees/2/#this
https://localhost:4443/employees/6/#this,https://localhost:4443/employees/5/#this
https://localhost:4443/employees/7/#this,https://localhost:4443/employees/5/#this
https://localhost:4443/employees/8/#this,https://localhost:4443/employees/2/#this
https://localhost:4443/employees/9/#this,https://localhost:4443/employees/5/#this
Fuseki 3.16.0 returns 9 results:
employee,reportsToEmployee
https://localhost:4443/employees/1/#this,https://localhost:4443/employees/2/#this
https://localhost:4443/employees/2/#this,
https://localhost:4443/employees/3/#this,https://localhost:4443/employees/2/#this
https://localhost:4443/employees/4/#this,https://localhost:4443/employees/2/#this
https://localhost:4443/employees/5/#this,https://localhost:4443/employees/2/#this
https://localhost:4443/employees/6/#this,https://localhost:4443/employees/5/#this
https://localhost:4443/employees/7/#this,https://localhost:4443/employees/5/#this
https://localhost:4443/employees/8/#this,https://localhost:4443/employees/2/#this
https://localhost:4443/employees/9/#this,https://localhost:4443/employees/5/#this
So far so good -- the results are identical. Now I append an OPTIONAL
to the end of the query:
PREFIX schema: <https://schema.org/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX sioc: <http://rdfs.org/sioc/ns#>
SELECT ?employee ?reportsToEmployee ?reportsToEmployeeLabel WHERE {
GRAPH ?docGraph {
?doc sioc:has_container <https://localhost:4443/employees/>;
foaf:primaryTopic ?employee.
OPTIONAL { ?employee schema:sponsor ?reportsToEmployee. }
}
OPTIONAL {
GRAPH ?reportsToEmployeeLabelGraph { ?reportsToEmployee
<http://purl.org/dc/terms/title> ?reportsToEmployeeLabel. }
}
}
ORDER BY ?doc
Dydra returns 9 results:
employee,reportsToEmployee,reportsToEmployeeLabel
https://localhost:4443/employees/1/#this,https://localhost:4443/employees/2/#this,Fuller
https://localhost:4443/employees/2/#this,,
https://localhost:4443/employees/3/#this,https://localhost:4443/employees/2/#this,Fuller
https://localhost:4443/employees/4/#this,https://localhost:4443/employees/2/#this,Fuller
https://localhost:4443/employees/5/#this,https://localhost:4443/employees/2/#this,Fuller
https://localhost:4443/employees/6/#this,https://localhost:4443/employees/5/#this,Buchanan
https://localhost:4443/employees/7/#this,https://localhost:4443/employees/5/#this,Buchanan
https://localhost:4443/employees/8/#this,https://localhost:4443/employees/2/#this,Fuller
https://localhost:4443/employees/9/#this,https://localhost:4443/employees/5/#this,Buchanan
Fuseki 3.16.0 returns 2400+ results:
employee,reportsToEmployee,reportsToEmployeeLabel
https://localhost:4443/employees/1/#this,https://localhost:4443/employees/2/#this,Fuller
https://localhost:4443/employees/2/#this,https://localhost:4443/,Root
https://localhost:4443/employees/2/#this,https://localhost:4443/categories/,Categories
https://localhost:4443/employees/2/#this,https://localhost:4443/categories/1/,Beverages
https://localhost:4443/employees/2/#this,https://localhost:4443/categories/1/#this,Beverages
https://localhost:4443/employees/2/#this,https://localhost:4443/categories/2/,Condiments
https://localhost:4443/employees/2/#this,https://localhost:4443/categories/2/#this,Condiments
https://localhost:4443/employees/2/#this,https://localhost:4443/categories/3/,Confections
https://localhost:4443/employees/2/#this,https://localhost:4443/categories/3/#this,Confections
https://localhost:4443/employees/2/#this,https://localhost:4443/categories/4/,Dairy
Products
https://localhost:4443/employees/2/#this,https://localhost:4443/categories/4/#this,Dairy
Products
https://localhost:4443/employees/2/#this,https://localhost:4443/categories/5/,Grains/Cereals
....
Dydra's result is the one I'm going after, and is based on my
understanding of OPTIONAL. But is it actually correct?
And if Dydra is correct, what is Fuseki doing here? I would have
expected the ?reportsToEmployee bindings from the appended OPTIONAL to
be joined against the first result (without OPTIONAL), but that is not
the case?
Thanks.
Martynas
