Hey look - DabbleDB has plugin capabilities, and it's simple:

So, with this talk of services over HTTP, you might be rightly concerned that the next step is to discuss Dabble’s XML web service protocol. You’ll be relieved to find out that Dabble plugins don’t speak XML. They speak CSV (Comma-Separated Values). Dabble passes UTF-8 encoded plain-text, comma-separated data in and expects UTF-8 encoded plain-text, comma-separated data out. Each row in your Dabble application generates a line in a CSV stream. To process a derived field for a Dabble category, you’ll simply need to process each incoming line of CSV and generate a new line of CSV as a response. If you’ve used a UNIX-based operating system, you’re probably familiar with the notion of pipes. The output of one program is piped into the input of another, creating a filter chain. This is conceptually the same as the way Dabble’s plugin IO works. Nice and simple.

Looks pretty neat.