public function getDomain()
    {
        $returnValue = null;
        if (is_null($this->domain)){
        	$this->domain = new core_kernel_classes_ContainerCollection(new common_Object(__METHOD__));
			$domainValues = $this->getPropertyValues($this->getProperty(OntologyRdfs::RDFS_DOMAIN));
			foreach ($domainValues as $domainValue){
				$this->domain->add($this->getClass($domainValue));
			}
		}
		$returnValue = $this->domain;
        

        return $returnValue;
    }