Each kind of datasource will need its own kind of configuration data, and such configuration should be sharable among different application-level 'meta-configurations'. So the application config can reference specifier strings for other datasources, and the datasource subclass must acquire its config through that specifier. Perhaps the specifier could be a url, so that configs can be shared through a http server. Or maybe better would be to pass the datasource factory a big long string of configuration info, where that info might come from a file or from a 'config server', http, or sql, and the datasource implementations would only have to create and parse their own data.

I like the SQL config idea. Datasources should be able to serve configurations as well as data, where a configuration is just a blob of text attached to a name, with description and such. Different users on the plane can create their own configuration, write them back to the database, where other users can pull up that configuration. See Chapter 4, Configuration.