Google has announced that Google Reader has begun adoption of the PubSubHubbub protocol for shared items. This is a simple, open, server-to-server web-hook based pubsub (publish/subscribe) protocol, as defined on this Google Code page.
Here's a visual overview of what that means:
"All shared item pages have feeds, and now all of those feeds will ping a hub (and there's a <link rel="hub" .../> element in them)," explains Mihai Parparita on the Google Reader Blog. "This means that if you (as a web app developer) would like to more efficiently and quickly monitor Reader shares, you just have to subscribe at the hub to be notified of changes in real-time. If you want to learn more about PubSubHubbub and how it works, see the site and protocol definition."
Google names FriendFeed specifically as a place that takes advantage of such pinging. If you have added your shared items to your FriendFeed account, you and your friends will see them there in real-time. This means they will appear in FriendFeed's real-time search engine.
Adding the PubSubHubbub support was one of the famous 20% projects of a few Googlers. They cite the project as a contributor to making the web a faster place, which of course is a big initiative of Google these days.
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