PREFIX ppeo: <http://purl.org/ppeo/PPEO.owl#>
PREFIX unlock: <http://m-unlock.nl/ontology/>
SELECT ?investigation ?study ?observationUnit ?assay ?sample
WHERE {
	?investigation a jerm:Investigation .
	?investigation jerm:hasPart ?study .
	?study a jerm:Study .
    # Up to study is obligatory
    OPTIONAL {
        ?study jerm:hasPart ?observationUnit .
        ?observationUnit jerm:hasPart ?sample .
        ?sample jerm:hasPart ?assay .
    }
}