A Subject Relation is a URI. It is comprised of a ContextId URI combined with an optional identifier string called a SubjectId. The SubjectId, if present, uniquely identifies a Digital Subject within the Context identified by the ContextId. The SubjectId may only be omitted when the Context identified by the ContextId contains exactly one Digital Subject.
Two kinds of Relations are defined: a URIrelation (Hash URI) and XRIrelation. The former is consistent with one of the two proposed W3C's Cool URIs approaches. The latter is an XRI as defined by XRI Syntax 2.0.
relation = URIrelation / XRIrelation URIrelation = contextURI [ "#" subjectId ] XRIrelation = contextXRI [ "//" subjectId ]