Intro to the Atom Publishing Protocol (AtomPub)
Joe Gregorio gives an overview of the Atom Publishing Protocol.
RFC4287:
http://www.ietf.org/rfc/rfc4287.txt
RFC5023:
http://www.rfc-editor.org/rfc/rfc5023.txt
Intro to Google Data:
http://www.youtube.com/watch?v=ADos_xW4_J0
The Google Data APIs:
http://code.google.com/apis/gdata