def getDataset(self, itemId):
        """gets a dataset class"""
        if self._url.lower().find('datasets') > -1:
            url = self._url
        else:
            url = self._url + "/datasets"
        return OpenDataItem(url=url,
                            itemId=itemId,
                            securityHandler=self._securityHandler,
                            proxy_url=self._proxy_url,
                            proxy_port=self._proxy_port)
gets a dataset class