Google today released a new Social Graph API. This is a "good and powerful" service for mining relationships between people. This API is based on Google's search for profile pages linked in social networks and blogs. At the same time, this service will also search for relationships between people contained within these data. This can be achieved through standard links between blogs that indicate implicit relationships, or data indicating explicit relationship statuses, such as XFN (XHTML Friends Network), FOAF (Friend of a Friend format), and other standard RDF structures.
In this API, it is stipulated that "sites appearing in Google search services that contain XFN or FOAF data will automatically be included in the Social Graph API." It also includes some public profile data, such as those found on MySpace. Additionally, Google provides some very simple example programs so you can understand which interactive connections your site has. You can also check out Tim O'Reilly's article. There is also this video tutorial from Brad Fitzpatrick, which is another good way to quickly understand the API.
Developers can use web addresses that represent individuals, like blog URLs, to search across network services. The system will return a list of relevant connections and their relationships in JSON format. Plaxo uses this API to provide all the relevant information you want to add to your profile, thus reducing the time spent when new users register.
This may be Google's first step towards innovation around social search (see joining DataPortability.org and Sarah Perez points out). In Tim O'Reilly's view, "this is an innovative move in the field of social networking. It takes a big step towards the fair ground of open standards and intelligent social applications."