When users share from a blog’s old feed while others use FeedBurner and you don’t canonicalize before aggregating, you can’t reliably count how many times a story has been shared. Canonicalizing something means to find the “standard state” of it
The Google data APIs provide a standard protocol for reading and writing data on the web. These APIs use either Atom or RSS. They also have a feed-publishing system that consists of the Atom publishing protocol plus some extensions for handling queries.