Peter Forret emailed me with an idea: Yahoo Pipes + a query language = SWQL (structured query language for rss).

I think it’s great, this could be implemented as a library for which we could then develop a PHP wrapper. The PHP would look something like:

$swql_connect(“http://pipes.yahoo.com/api”, “username”, “password”); // where the yahoo pipes API serves as the database engine.
$res = swql_query(“SELECT title, description, enclosure FROM rss:http://podcast.example.com/feed/ as rss_feed WHERE len(rss_feed.enclosure) > 0 ORDER BY rss_feed.title”);

Brilliant!