FB
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At Facebook's core is the social graph; people and the connections they have to everything they care about. Historically, Facebook has managed this graph and has expanded it over time as we launch new products (photos, places, etc.). In 2010, we introduced an early version of Open Graph, an extension of the social graph, via the Open Graph protocol , to include 3rd party web sites and pages that people liked throughout the web. We are now extending the Open Graph to include arbitrary actions and objects created by 3rd party apps and enabling these apps to integrate deeply into the Facebook experience. After a user adds your app to their Timeline, app specific actions are shared on Facebook via the Open Graph.
Open Graph protocol - Facebook Developers
Authentication - Facebook Developers
Please note: On May 1, 2012, the offline_access permission will be deprecated. If you are building a new application you shouldn't use this permission. Instead please check the Deprecation of Offline Access Permission document which explains how to start using access tokens that are valid for up to 60 days Authentication gives your app the ability to know the identity of a Facebook user, and to read and write data via Facebook's APIs . The Facebook Platform uses OAuth 2.0 for authentication and authorization.