The Facebook Platform is a software environment provided by the social networking service Facebook for third-party developers to create their own applications and services that access data in Facebook. It was launched in 2010. The platform offers a set of programming interfaces and tools which enable developers to integrate with the open "social graph" of personal relations and other things like songs, places, and Facebook pages. Applications on facebook.com, external websites, and devices are all allowed to access the graph.
Facebook launched the Facebook Platform on May 24, 2007, providing a framework for software developers to create applications that interact with core Facebook features. A markup language called Facebook Markup Language was introduced simultaneously; it is used to customize the "look and feel" of applications that developers create. Using the Platform, Facebook launched several new applications, including Gifts, allowing users to send virtual gifts to each other, Marketplace, allowing users to post free classified ads, Events, giving users a method of informing their friends about upcoming events, Video, letting users share homemade videos with one another, and social network game, where users can use their connections to friends to help them advance in games they are playing. Many of the popular early social network games would combine capabilities, for instance, one of the early games to reach the top application spot, (Lil) Green Patch, combined virtual Gifts with Event notifications to friends and contributions to charities through Causes.
Third party companies provide application metrics, and several blogs arose in response to the clamor for Facebook applications. On July 4, 2007, Altura Ventures announced the "Altura 1 Facebook Investment Fund," becoming the world's first Facebook-only venture capital firm.
On August 29, 2007, Facebook changed the way in which the popularity of applications is measured, to give attention to the more engaging applications, following criticism that ranking applications only by the number of people who had installed the application was giving an advantage to the highly viral, yet useless applications. Tech blog Valleywag has criticized Facebook Applications, labeling them a "cornucopia of uselessness." Others have called for limiting third-party applications so the Facebook user experience is not degraded.
Applications that have been created on the Platform include chess, which both allow users to play games with their friends. In such games, a user's moves are saved on the website, allowing the next move to be made at any time rather than immediately after the previous move.
By November 3, 2007, seven thousand applications had been developed on the Facebook Platform, with another hundred created every day. By the second annual f8 developers conference on July 23, 2008, the number of applications had grown to 33,000, and the number of registered developers had exceeded 400,000.
Facebook integration was announced for the Xbox 360 and Nintendo DSi on June 1, 2009 at E3. On November 18, 2009, Sony announced an integration with Facebook to deliver the first phase of a variety of new features to further connect and enhance the online social experiences of PlayStation 3. On February 2, 2010, Facebook announced the release of HipHop for PHP as an opensource project. Mark Zuckerberg said that his team from Facebook is developing a Facebook search engine. “Facebook is pretty well placed to respond to people’s questions. At some point, we will. We have a team that is working on it", said Mark Zuckerberg. For him, the traditional search engines return too many results that do not necessarily respond to questions. “The search engines really need to evolve a set of answers: 'I have a specific question, answer this question for me.'"
On June 10, 2014, Facebook announced Haxl, a Haskell library that simplified the access to remote data, such as databases or web-based services. 
High-level Platform components
The Graph API is the core of Facebook Platform, enabling developers to read from and write data into Facebook. The Graph API presents a simple, consistent view of the Facebook social graph, uniformly representing objects in the graph (e.g., people, photos, events, and pages) and the connections between them (e.g., friend relationships, shared content, and photo tags).
Facebook authentication enables developers’ applications to interact with the Graph API on behalf of Facebook users, and it provides a single-sign on mechanism across web, mobile, and desktop apps.
Social plugins – including the Like Button, Recommendations, and Activity Feed – enable developers to provide social experiences to their users with just a few lines of HTML. All social plugins are extensions of Facebook and are specifically designed so no user data is shared with the sites on which they appear.
Open Graph protocol
The Open Graph protocol enables developers to integrate their pages into the social graph. These pages gain the functionality of other graph objects including profile links and stream updates for connected users. As an example, the following is the Open Graph protocol markup for text on Software Master Center:
<meta property="og:type" content="product" />
<meta property="og:url" content="http://www.softwaremastercenter.com/text_20605-1_software.html" />
<meta property="og:image" content="http://regnow.img.digitalriver.com/vendor/20605/Boxshot1.jpg" />
<meta property="og:site_name" content="Software Master Center" />
<meta property="og:description" content="Easily enter international/foreign characters in Internet Explorer." />
Facebook uses iframes to allow third-party developers to create applications that are hosted separately from Facebook, but operate within a Facebook session and are accessed through a user's profile. Since iframes essentially nest independent websites within a Facebook session, their content is distinct from Facebook formatting.
Facebook stopped accepting new FBML applications on March 18, 2011, but continued to support existing FBML tabs and applications. Since January 1, 2012 FBML was no longer supported, and FBML no longer functioned as of June 1, 2012.
Facebook Connect, also called Log in with Facebook, like OpenID, is a set of authentication APIs from Facebook that enable Facebook members to log onto third-party websites, applications, mobile devices and gaming systems with their Facebook identity. While logged in, users can connect with friends via these media and post information and updates to their Facebook profile. Developers can use these services to help their users connect and share with their Facebook friends on and off of Facebook and increase engagement for their website or application.
Originally unveiled during Facebook’s developer conference, F8, in July 2008, Log in with Facebook became generally available in December 2008. According to an article from The New York Times, "Some say the services are representative of surprising new thinking in Silicon Valley. Instead of trying to hoard information about their users, the Internet companies (including Facebook, Google, MySpace and Twitter) all share at least some of that data so people do not have to enter the same identifying information again and again on different sites."
Log in with Facebook cannot be used by users in locations that cannot access Facebook (e.g. China), even if the third-party site is otherwise accessible from that location.
In February 2011, Facebook began to use the hCalendar microformat to mark up events, and the hCard for the events' venues, enabling the extraction of details to users' own calendar or mapping applications.
The UI framework for the mobile website is based on Xhp, Javelin and WURFL. The mobile platform has grown dramatically in popularity since its launch. In December 2012, the number of users signing into the site from mobile devices exceeded web-based logins for the first time.
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The Guardian expressed concerns that users publishing content through a third party provider are exposed to losing their web positioning if their service is removed; and the open graph could force connecting web presence to Facebook social services even for people using their own publishing channels.
Primarily attempting to create viral applications is a method that has certainly been employed by numerous Facebook application developers. Stanford University even offered a class in the Fall of 2007, entitled, Computer Science (CS) 377W: "Create Engaging Web Applications Using Metrics and Learning on Facebook". Numerous applications created by the class were highly successful, and ranked amongst the top Facebook applications, with some achieving over 3.5 million users in a month.
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