term = $term; $this->scheme = $scheme; $this->label = $label; } public function __toString() { // There is no $this->data here return md5(serialize($this)); } public function get_term() { if ($this->term !== null) { return $this->term; } else { return null; } } public function get_scheme() { if ($this->scheme !== null) { return $this->scheme; } else { return null; } } public function get_label() { if ($this->label !== null) { return $this->label; } else { return $this->get_term(); } } }