We can all agree that APIs are great. They open up silos to a wealth of data and functionality, but the vast majority of these Web APIs use the HTTP request-response model, requiring the client to make a request to a server and wait for a response in an interactive fashion. This is fine for the majority of our examples so far, such as sending a Tweet, adding a contact, etc. But what about when you actively want to retrieve updates about a particular resource, such as who’s talking about my company on Twitter today? You wouldn’t have someone sitting there issuing a request every 5 minutes would you? No, ideally you want to be notified in a real-time fashion when someone is talking about your company or when something hap....