Google data APIs ("GData" for short) is a new Google protocol for "reading and writing data on the web". It's described here:
"GData combines common XML-based syndication formats (Atom and RSS) with a feed-publishing system based on the Atom publishing protocol, plus some extensions for handling queries."
So GData is a new protocol, but "based on Atom 1.0 and RSS 2.0." Actually at first glance it seems to be a mix of RSS and APIs. It bears a bit of resemblance to the Atom syndication format, with its extensibility and publication protocol. But apparently GData does more than Atom:
"In various contexts, it's useful to be able to send a query to a server and receive a response containing a list of matching results. Neither Atom nor RSS provides a way to do that, but GData does."
When they talk about possible uses, it looks like Google is targeting its own increasingly integrated web apps:
"All sorts of services can provide GData feeds, from public services like blog feeds or news syndication feeds to personalized data like email or calendar events or task-list items."
It's an interesting development by Google and is sure to ruffle a few feathers in the RSS and Atom camps, both of which are sensitive and prickly at the best of times. More on this as I investigate.