Constructing a sparql query using rdf4j

Question

I'm trying to construct a SPARQL query using the rdf4j documentation: https://rdf4j.org/documentation/tutorials/sparqlbuilder/

I am a newbie to java (and stackoverflow, apologies if this is poorly written), but I think I have included the right beginning steps. I have instantiated a select query, a prefix and a variable in the following way:

    SelectQuery draftQuery = Queries.SELECT();

    Prefix default = SparqlBuilder.prefix("dc", Rdf.iri("url"));

    Variable draftCount = SparqlBuilder.var("draftCount");

url has been substituted with the right prefix

The query I am trying to write is: SELECT ?x WHERE { :team_1 :draftCount ?x}, but ?x has no rdf:type and is simply a value that is attached to :draftCount. I have no idea how to write it as a SPARQL query within java, because from what I understand within the docs, the example included where the product is a book, the product has rdf:type "book". I don't want to query multiple variables (e.g. :team_1 ?x ?y) because there are other triples attached to the team and I want to query them separately. I want to have another SPARQL query later that is similar but is SELECT ?x WHERE { :team_1 :completedCount ?x},

How can I write this query? This is what I have so far:

    draftQuery.prefix(default).select(draftCount)

not sure what exactly you are asking for, but the tutorial is quite good from my point of view. Why are you not doing exactly what is shown in the first example there? Why do you think `draftCount` is a variable? In your query `SELECT ?x WHERE { :team_1 :draftCount ?x}` it is an RDF predicate, or not? I mean, it's called `:draftCount` which is clearly a prefixed URI. — UninformedUser, Apr 06 '21 at 12:04

score 4 · Accepted Answer · answered Apr 07 '21 at 00:30

You made a good start, but you are mixing up variables and IRIs: :team_1 and :draftCount are IRIs in your query, not variables. Only ?x is a variable. Since you are using the default namespace for your IRs, just create a Prefix object for the default namespace, like so:

Prefix defaultNs = SparqlBuilder.prefix(Rdf.iri("http://example.org/"));

and then you can use that to create Iri objects for use in the query, like so:

Iri team1 = defaultNs.iri("team_1");

To add a relation other than rdf:type using the SparqlBuilder, use the .has method.

Putting it all together, to produce this SPARQL query string:

PREFIX: <http://example.org/>
SELECT ?x WHERE { :team_1 :draftCount ?x}

You do this:

Prefix defaultNs = SparqlBuilder.prefix(Rdf.iri("http://example.org/"));
Iri team_1 = defaultNs.iri("team_1"), draftCount = defaultNs.iri("draftCount");
Variable x = SparqlBuilder.var("x");
        
SelectQuery query = Queries.SELECT()
            .prefix(defaultNs)
            .select(x)
            .where(team_1.has(draftCount, x));

System.out.println(query.getQueryString());

Constructing a sparql query using rdf4j

1 Answers1