This might be overly complicated, but my subgraph thought was something along the lines of (this example is the totally non-existent DC-as-relationships):
/graph/{pid}/DC is a subgraph defined as:
GRAPH ?g {
<info:fedora/$pid> ?p ?o .
?p <rdfs:isDefinedBy> <http://purl.org/dc/elements/1.1/>
}
and the REST API works along the lines of:
GET /graph/{pid}/DC STMT:=SELECT
PUT /graph/{pid}/DC STMT:=INSERT body
POST /graph/{pid}/DC?predicate={p}&object={o}&type={t} STMT:=INSERTDELETE /graph/{pid}/DC?predicate={p}&object={o}&type={t} STMT:=DELETE
$STMT
WHERE { ?g }
in which Fedora loads the <rdfs:isDefinedBy> statements for the DC core properties, or the Fedora system properties, etc.