Thanks, that solves the problem and I'll stick to it for now.
Nonetheless, is it possible to automatically infer being an instance of the
hypothetical class "YoungestPerson" ("the person with the lowest foaf:age
aggregate by house") in Apache Jena as described above? Ideally, I would
prefer to separate my conceptual/declarative model from raw data
manipulation using SPARQL. I am new to RDF & ontologies and I am not sure
to what extent keeping those two is possible and if it is worth to actually
invest a lot of time into that.
Best regards,
Jakub
niedz., 5 gru 2021 o 10:12 Lorenz Buehmann <
buehm...@informatik.uni-leipzig.de> napisał(a):
> Hi,
>
>
> the common pattern in SPARQL is to get the aggregated value in an inner
> query first, then in the outer query get the entity with the aggregated
> value:
>
> SELECT ?house ?person ?lowestAge {
> ?person foaf:age ?lowestAge .
> ?person covidepid:livesIn ?house .
>
>
> {SELECT ?house (min(?age) as ?lowestAge)
> WHERE {
> ?person foaf:age ?age .
> ?person covidepid:livesIn ?house .
> }
> GROUP BY ?house}
> }
>
>
>
> On 03.12.21 02:16, Jakub Jałowiec wrote:
> > Hi,
> > I would appreciate any help with the following problem. I have a bunch of
> > (foaf:Persons, myOntology:livesIn, myOntology:Place) triples. I am trying
> > to find the youngest person in each myOntology:Place (i.e. the person
> with
> > the earliest value of foaf:age for each myOntology:Place).
> > What I've tried so far were:
> > - OWL complex classes (Class Expression Syntax (protegeproject.github.io
> )
> > <http://protegeproject.github.io/protege/class-expression-syntax/>) -
> per
> > my understanding they have too weak expressivity to express aggregates
> > among other individuals associated with them
> > - SPARQL query - something along those lines would work fine but I do not
> > know how to retrieve the IRI of the youngest person:
> >
> >> SELECT ?house (min(?age) as ?lowestAge)
> >> WHERE {
> >> ?person foaf:age ?age .
> >> ?person covidepid:livesIn ?house .
> >> }
> >> GROUP BY ?house
> >
> > I am curious if extraction of the lowest foaf:age value among a group of
> > people could be achieved using Apache Jena rules. From the documentation
> (
> > https://jena.apache.org/documentation/inference/#rules) it seems to me
> that
> > the closest it gets to it is to write my custom built-in function that
> > would do exactly that. Is that correct?
> >
> > Best regards,
> > Jakub
> >
>
