public function getFirstExpression()
    {
        $returnValue = null;

        
        if(empty($this->firstExpression)){
        	$property = new core_kernel_classes_Property(RulesRdf::PROPERTY_FIRST_EXPRESSION);
			$this->firstExpression = new core_kernel_rules_Expression($this->getUniquePropertyValue($property)->getUri());
        }
		$returnValue = $this->firstExpression;
        

        return $returnValue;
    }