Advertisements Here is my simple working Sparql query: SELECT DISTINCT ?period ?start ?end WHERE { ?period isA "Period". OPTIONAL { ?period hasStart ?start }. #hasStart OPTIONAL { ?period hasEnd ?end }. #hasEnd } The thing is I’d like to add a variable in the select clause which is the duration between ?end and ?start, like… Read More SPARQL : Handle NULL values returned by OPTIONAL() keyword