An association between two Entities where the playing Entity is considered in some way "part" of the scoping Entity, e.g., as a member, component, ingredient, or content. Being "part" in the broadest sense of the word can mean anything from being an integral structural component to a mere incidental temporary association of a playing Entity with a (generally larger) scoping Entity.
\nhttp://terminology.hl7.org/CodeSystem/v3-RoleClass
where concept is-a PART