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Programming Social Applications by Jonathan LeBlanc

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Building on the Foundation of PubSubHubbub

We’ve already seen how the PubSubHubbub protocol can be used to easily push out updates from a publisher to a series of subscribers, but there is one piece missing in its flow.

Let’s use a practical example to identify this issue. Say a news publisher has a comment widget placed on each news story to allow people to discuss the topic being displayed. This publisher uses a centralized PubSubHubbub hub to push out updates to the content and any recent comments on the article to all subscribers to its feed.

This process works perfectly well to ensure that all of the feed subscribers have the most up-to-date content from the publisher, but what happens if the subscriber site uses the updated comments to augment its existing comment flow? The subscriber may have users of its own that are continuing the conversation beyond what is reflected on the publisher site. If there are many subscribers, this equates to many different conversations seeded with comments from the feed of a publisher that isn’t aware of what is being said in those conversations.

This is one such instance where the Salmon protocol can play a vital role. It can unify the conversation threads between the publisher and a series of trusted subscribers. In doing so, it aggregates these fragmented conversations into a single discussion within an interrelated network of sites.

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