public async Task Observe(With.Component.IIdentity client, With.Component.IIdentity entity, With.Component.IIdentity source, With.Component.IIdentity observable)
{
string registrationKey = Registration.Key.For(client, entity);
Registration.IInstance registration;
if (_registrations.TryGetValue(registrationKey, out registration))
{
await _hub.Observe(client.AsDto(), entity.AsDto(), source.AsDto(), observable.AsDto());
}
}