SERVICE is a feature of SPARQL 1.1 that allows an executing query to make a SPARQL protocol to another SPARQL endpoint.
It is very helpful to retrieve labels, as it reduces the complexity of SPARQL queries, but is not implemented in sparql-client yet.
@s0rin, I added support for SERVICE on the develop branch (see inline documentation). As with other support, some patterns will be too complicated to express using SPARQL::Query.
SERVICE is a feature of SPARQL 1.1 that allows an executing query to make a SPARQL protocol to another SPARQL endpoint. It is very helpful to retrieve labels, as it reduces the complexity of SPARQL queries, but is not implemented in sparql-client yet.