Since 2006, google collects API programming interfaces in the Google Data (gdata) project. At their website, you find links to google docs, calendar, spreadsheet, youtube, and more.
It is a one-stop place to find interfaces for the various google services. For Semantic Web developers, it is also a good overview how google shapes its interfaces to its web-based applications. Get inspired by the pros.
Especially the GData protocol and data format is worth a look. It’s a generic API for getting and querying data, based on RSS 2.0 and Atom.
In the GData reference, you find a description of the Atom extensions and a simple query-format extending it.
Assuming a feed is hosted at the URI http://www.example.com/feeds/jo, then elements within the feed can be queried with the following URI:
A kind of “easy going sparql”.
In their own words:
The Google data APIs provide a simple standard protocol for reading and writing data on the web.
These APIs use either of two standard XML-based syndication formats: Atom or RSS. They also have a feed-publishing system that consists of the Atom publishing protocol plus some extensions (using Atom’s standard extension model) for handling queries.
Many Google services support the Google data API protocol.