Google today released their Social Graph API, a very powerful new service to facilitate the discovery of publicly declared relationships between people. The API is based on Google crawling the web and searching for pages that are associated with an individual - profile pages in many social networks, or blogs and websites associated with one person. Along with that, the service searches for relationships between people that are represented in this data. This can some from standard links between blogs that imply a relationship, or explicitly stated relationships of the formats that are used in social networks XFN, the XHTML Friends Network, or FOAF, the Friend of a Friend format, an RDF structure. We've added a new Social Graph API Profile in our directory.
In the Google Code site for this API it states that "sites that appear in the Google Web Search are automatically included in the Social Graph API if they contain XFN or FOAF data. Additionally, data is included from some other publicly declared profiles, such as MySpace." Along with the API Google has released a very handy demo application that lets you interactively see the links about your own sites, or as Tim O'Reilly describes it debug your Social Graph (our profile of it here). For a good quick introduction to the API check this video from Google's Brad Fitzpatrick:
A developer queries the web service by giving it a node that represents the person, like a blog's web address, and it returns in JSON format the list of nodes connected to it and the nature of the relationship. One user of this API is Plaxo who uses it to reduce new account setup time by taking your publicly available relationship information to suggest links you may want to include in your profile.
The announcement is consistent with Google's joining DataPortability.org, and as Sarah Perez points out, may be a first step towards Google's stated desire to innovate around social search. Tim O'Reilly sees it as "a game-changing play in the social networking space. It's a huge step towards open standards and a level playing field in smart social apps."