@PathParam("user_id") String userId, @PathParam("owner_id") String ownerId,
@PathParam("name") String name) {
final Session session = credentials.buildSession(userDAO, userId);
final User owner = findUser(ownerId);
final Document doc = findDocument(owner, name);
checkLinkage(doc, session.getUser());
doc.unlinkUser(session.getUser());
documentDAO.saveOrUpdate(doc);
return Response.noContent().build();
}