Slice(Project(Extend(AggregationJoin(Aggregation(??agg1: ?s, SAMPLE,
                                                 {},
                                                 G1=Group((?s),
                                                    BGP( ?s <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://purl.org/ontology/bibo/article>)))),
                     ?s,
                     ??agg1),
              {?s}),
      0,
      20)