LATERAL: Binding already for ?label (same value)

[Martynas Jusevičius]

Hi,

I found a use case for LATERAL and I'm testing a query like this:

PREFIX worker: <https://example.org/ontology/worker#>
PREFIX wd:     <https://w3id.org/atomgraph/workday#>
PREFIX foaf:   <http://xmlns.com/foaf/0.1/>
PREFIX rdfs:   <http://www.w3.org/2000/01/rdf-schema#>
PREFIX owl:    <http://www.w3.org/2002/07/owl#>

CONSTRUCT {
  ?dgsWorker owl:sameAs ?wdWorker .
}
WHERE {
  ?dgsWorker a worker:Person ;
             rdfs:label ?label .

  LATERAL {
    SERVICE <http://localhost:8181/workday/sparql> {
      SELECT ?wdWorker ?label {
          ?wdWorker a wd:Worker ;
                    foaf:name ?label .
      }
    }
  }
}

It gets names from a local file and reconciles them against a virtual
SPARQL endpoint.
The query produces results but each SERVICE call prints a warning like this:

14:39:59 WARN  QueryIterCommonParent$ConverterExtend :: Binding already for
?label (same value)

What does this mean exactly? Does the query need reformulation to avoid
this?

Thanks.

Martynas