public function getDefinition()
 {
     $path = $this->basePath . DIRECTORY_SEPARATOR . $this->definitionName;
     if (!is_file($path) || !is_readable($path)) {
         throw new RuntimeException('The upgrade base path doesn\'t have a definition file for upgrading (' . $path . ')');
     }
     return sfSimpleYamlConfigHandler::replaceConstants(sfSimpleYamlConfigHandler::getConfiguration(array($path)));
 }