http://docs.oasis-open.org/cmis/CMIS/v1.0/cs01/cmis-spec-v1.0.html
CMIS Relationship object:
http://docs.oasis-open.org/cmis/CMIS/v1.0/cs01/cmis-spec-v1.0.html#_Toc243905402
CMIS Relationship Service:
http://docs.oasis-open.org/cmis/CMIS/v1.0/cs01/cmis-spec-v1.0.html#_Toc243905479
The Relationship Services (getObjectRelationships) are used to retrieve the dependent Relationship objects associated with an independent object.