public function addRole($label, $includedRoles = null, core_kernel_classes_Class $class = null)
    {
        $returnValue = null;

        $includedRoles = is_array($includedRoles) ? $includedRoles : array($includedRoles);
		$includedRoles = empty($includedRoles[0]) ? array() : $includedRoles;
		
		$classRole =  (empty($class)) ? new core_kernel_classes_Class(GenerisRdf::CLASS_ROLE) : $class;
		$includesRoleProperty = new core_kernel_classes_Property(GenerisRdf::PROPERTY_ROLE_INCLUDESROLE);
        $role = $classRole->createInstance($label, "${label} Role");
        
        foreach ($includedRoles as $ir){
        	$role->setPropertyValue($includesRoleProperty, $ir);	
        }
        
        $returnValue = $role;

        return $returnValue;
    }