Google on Friday launched a new application programming interface (API) to help developers make use of social networking relationship data.

The Google Social Graph API provides developers with a way to leverage social relationships in their applications and on their Web sites. "You can make it easy for users to bring their existing social connections into a new Web site and as a result, users will spend less time rebuilding their social networks and more time giving your app the love it deserves," explained Google engineer Brad Fitzpatrick in a blog post.

For example, a developer using the Social Graph API could create a button for a Web site that would allow a registered user to easily "add friends."

By making social data more portable, Google makes social networks less relevant. In keeping with its mission to organize and index the world's information, Google would prefer to see a single network, the Internet, through which any data can be accessed and, it's hoped, monetized through its ad platform.

If Google's vision proves appealing and social data loses its linkage to a specific social site, Facebook and MySpace may find their ability to retain users substantially diminished. Without the added value of social graph exclusivity, Facebook and MySpace become merely providers of Web hosting for the HTML averse. It's doubtful Facebook could sustain a valuation of $15 billion were it pitched as "Geocities, but with widgets."

It's not clear yet how well Google will be able to monetize social graph data; during the company's fourth quarter financial call Thursday, Google co-founder Sergey Brin observed that social network advertising hadn't performed as well as expected. But the company may yet find a way to use relationship data to target its ads more effectively, provided the privacy issues can be worked out.