PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX atom: <http://atomowl.org/ontologies/atomrdf#> PREFIX sioc: <http://rdfs.org/sioc/ns#> PREFIX sioct: <http://rdfs.org/sioc/types#> SELECT * WHERE { ?forum rdf:type sioct:MessageBoard . ?forum sioc:container_of ?post. OPTIONAL{ ?post atom:title ?title } . OPTIONAL{ ?post atom:published ?date } . }