public function find($identifier)
    {
        $identifier = (string) $identifier;

        //Resolve the real identifier in case an alias was passed
        while(array_key_exists($identifier, $this->_aliases)) {
            $identifier = $this->_aliases[$identifier];
        }

        //Find the identifier
        if($this->offsetExists($identifier))
        {
            $result = $this->offsetGet($identifier);

            if($result instanceof KObjectInterface) {
                $result = $result->getIdentifier();
            }
        }
        else  $result = null;

        return $result;
    }