Yahoo is swinging the doors of its Web platforms wide open to let outside developers create applications across its network of sites, as well as radically stitching together its online services under the social profile concept.

The idea is to let the hundreds of millions of people who use its Web mail, instant messaging, calendar, photo management, and other online services replicate the social experience that social networks like MySpace and Facebook have made so popular.

This means that Yahoo users will have a profile under which their Yahoo services will fall, and which users will be able to customize by adding applications. This profile will also simplify the map of connections between Yahoo users so that they can find each other and interact more easily and efficiently.

If Yahoo is able to bring this vision to reality, it could pose a major threat to the appeal of MySpace, Facebook, and other social networks, and give Yahoo the boost it has been seeking for years among Web users.

"It is rewiring Yahoo from the inside out, across all of our properties, to fundamentally open up those Web services and provide a consistent development model, a consistent deployment and consumer experience as well," said Ari Balogh, Yahoo's CTO, during a keynote at the Web 2.0 Expo in San Francisco on Thursday.

While Yahoo has had open APIs for a variety of its services for years, Balogh said this initiative will take those efforts to much greater lengths, and it will include streamlining the development process so that it's uniform for developers across Yahoo platforms, he said. "It includes opening it up in a way we have never done before. It's about making the entire Yahoo experience more social," he said.

The process is already ongoing, as Yahoo on Thursday announced the opening up in beta of its Search Monkey development environment, which lets external developers customize Yahoo search results to make them, in theory, more relevant and richer with information. Yahoo had announced its intention to do this in February.

Yahoo expects to hit more significant milestones in its opening-up process throughout the year, he said.

With this vision, Yahoo seems to be finally tossing out the window its failed and misguided attempts to compete against MySpace and Facebook by creating a straight-ahead social networking site, like its disappointing Yahoo 360.

Instead, Yahoo is going to attempt to harness its users worldwide, which have some 10 billion latent social relationships already established amongst themselves via their Yahoo Messenger contact lists, Yahoo Mail address books, and the like.

By unifying all Yahoo user profiles, Yahoo will create its own consistent social graph for the benefit of both consumers and developers, he said. From the social graph, Yahoo will be able to establish relevant connections among users, as well as event streams of what people are doing online, which are popular on Facebook and via FriendFeed.

"We don't think of social as a destination. We think of social as a dimension. It infuses every element of the consumer's experience on the Web," Balogh said.

Yahoo will also take care of making sure that people are in control of the applications they opt to add and thus share data with, as well as making sure that data is kept safe.

This story was updated on April 24, 2008