private function doVerb()
    {
        switch ($this->verb) {
            case "Identify":
                return $this->identify();
                break;
            case "ListMetadataFormats":
                return $this->listMetadataFormats();
                break;
            case "ListSets":
                return $this->listSets();
                break;
            case "ListRecords":
                return $this->listRecords();
                break;
            case "ListIdentifiers":
                return $this->listIdentifiers();
                break;
            case "GetRecord":
                return $this->getRecord();
                break;
            default:
                //shouldn't be possible to come here because verb was already checked, but just in case
                throw new BadVerbException("$this->verb is not a valid verb");
        }
    }