At the Forge - Thinking about APIs

The historical evolution of Web sites into applications.

Facebook, the social networking site started by Mark Zuckerberg, has become an extremely popular application on the Web. Facebook users can connect with friends, join groups of like-minded individuals and send messages to others. Early in 2007, Facebook became popular among developers, as well as users, for creating a developer API that goes far beyond the APIs I have described above. In a nutshell, Facebook invited developers to create and deploy new applications that are seamlessly integrated into the full Facebook experience.

Facebook isn't the only site that lets you incorporate your own code into the site. However, the style and methods of this integration are deeper on Facebook than I have seen elsewhere. In the Facebook model, your Web application still resides on your server, but its output is displayed inside the user's Facebook page, alongside other Facebook applications. This definitely is something new and exciting; I can't think of any other Web sites that make it possible for an independent developer to distribute code that integrates into the Web site. The fact that you can use whatever language and platform you prefer, communicating with Facebook in a certain way, marks the beginning of a new kind of API, one in which users can affect the Web service as seen by all users, not just one particular user. The only other site I can think of in this camp is Ning, Marc Andreessen's build-your-own-social-network site.

Moreover, Facebook has taken a page from Amazon and eBay, telling developers that they can go wild, using the Facebook network for commercial as well as nonprofit reasons. Google has had a long-standing policy of allowing access to its maps, for example, but only for publicly accessible Web sites and reasons. It remains to be seen whether Facebook's API will continue to be free of charge and open to all.

Something this sophisticated cannot use any one of the protocols that I mentioned above. Rather, Facebook uses a combination of protocols and techniques to communicate with your Web application, making it possible for your programs to display their output alongside other Facebook applications. Moreover, Facebook makes it possible for your application to grab certain pieces of the user's Facebook data, so even though your application doesn't have access to the back-end Facebook database, it still can know (and display) something about the user's friends. Your application even can send messages and notifications to the user's friends, although Facebook has discovered that this can lead to spamming, so it remains to be seen exactly what happens on this front.


Web sites used to be nothing more than an electronic method for publishing and reading basic information encoded in HTML. But, Web sites evolved into applications, which spawned the first generation of APIs that made it possible to read and write your data. Facebook is the first of the new generation of Web sites that look at themselves as a platform more than an application.

And, although Amazon, Google and eBay have demonstrated the importance and potential of a platform-centric view, Facebook is pioneering the incorporation of third-party applications. True, most Facebook applications created to date are simple or trivial. But, we can expect that these applications will become increasingly sophisticated and useful over time. Facebook's willingness to open up to third-party developers is good for everyone—except for competing sites, such as MySpace and LinkedIn, which still appear to see themselves as standalone sites, rather than platforms for new applications.

This month, I explained why I find Facebook's API to be new and exciting. Next month, we'll look at how you can create your own Facebook applications. Even if you aren't interested in creating applications for Facebook, you owe it to yourself to see how the latest generation of Web applications allow themselves to be modified, not just queried.

Reuven M. Lerner, a longtime Web/database developer and consultant, is a PhD candidate in learning sciences at Northwestern University, studying on-line learning communities. He recently returned (with his wife and three children) to their home in Modi'in, Israel, after four years in the Chicago area.