Yahoo will launch its platform for Web developers this week, part of an effort to attract more visitors by adding Facebook-like social networking features to Yahoo's Web sites.

Yahoo hopes to drive more traffic to its sites by allowing people to share information about their interests and activities with friends. Like on Facebook, they'll be able to create a network of connections and send alerts to those people when they upload photos to Flickr or comment on a story at Yahoo News, for example.

The platform will extend to non-Yahoo sites such as Amazon and Digg, so that users will be able to see from within Yahoo's Web sites what their friends have been doing elsewhere on the Web. And third-party sites will be able to publish user activity back into the Yahoo network, which could help those sites draw more visitors.

The search company is making the data it stores about users -- such as their contacts, interests and location -- available for developers to build their applications. End users will be able to regulate which of their information friends and developers can see, said Yahoo officials, who previewed the platform in San Francisco on Friday.

It's an ambitious project that required Yahoo to "rewire" its properties to create a single underlying platform that connects them all. Those services existed in the past as "silos" that allowed for little interaction between them, said Ash Patel, executive vice president with Yahoo's Audience Product Division.

"The platform is how we start rewiring and reforming the user experience," he said.

Yahoo launched the first piece of the puzzle last week, a site called Yahoo Profiles where end users can manage their activities, interests and social connections in one place. Next week will mark the launch of the developer component. It's built on top of Yahoo's existing network infrastructure and consists broadly of three layers.

The first is the Yahoo Social Platform, a repository where Yahoo stores the personal data about its users, along with their "social graph," or information about who their friends are. Above that is the Application Platform, which provides the development framework. And above that is the Yahoo Query Language, which developers will use to pull personal user data from Yahoo's servers and write their programs. YQL is very similar to the widely used SQL database language, according to Yahoo.

The platform also makes use of public APIs such as Open Social, for aggregating user data from other social networking sites, and OAuth, a protocol for consuming and publishing personal data. The tools and documentation will be available for free download next week from the Yahoo Developer Network, said Jay Rossiter, head of Yahoo's Open Strategy project. He wouldn't say exactly which day.