PREFIX atom: <http://atomowl.org/ontologies/atomrdf#>
PREFIX sioc: <http://rdfs.org/sioc/ns#>
PREFIX sioct: <http://rdfs.org/sioc/types#>
SELECT DISTINCT ?post, ?title
WHERE
{
?forum a sioct:BookmarkFolder .
?forum sioc:container_of ?post.
OPTIONAL{?post atom:title ?title }.
}