Facebook won the loyalty of more than 800 million users largely by getting them into the habit of visiting again and again to see the latest updates, comments, and photos posted by friends. Now the site will also let outside apps provide even more content, and it will encourage people to spend time looking back over activity from months or even years ago. New features introduced at an event in San Francisco last night will enable users to automatically record their eating, reading, exercise, and other habits over time, share them with friends, and review their previous actions.

The key to the new features is an update to the Timeline page that Facebook founder Mark Zuckerberg introduced at his company's F8 event last September. Now, with a user's permission, third-party websites and mobile apps can record details of what the person is doing and automatically feed that information to the person's Timeline page through a "Timeline app" that sends the data to Facebook and provides the necessary permission and privacy settings.

"Your timeline is not just a way to tell your story based on what you're doing on Facebook, but using your activity out in the rest of the world as well," said Carl Sjogreen, director of platform products at Facebook, at the launch event.

Enthusiasts and researchers have experimented with comprehensively logging their lives for years. In 1998, for example, Microsoft researcher Gordon Bell began trying to digitally capture as much as he could about everything he did. But Bell and others have often found that browsing and reviewing their records presented a greater challenge than capturing them. Facebook's new design could help people do both.

Facebook's hope is not just to hook in users with more experiences, but also to make use of the new trove of data that Timeline apps will provide. The information could help the company's efforts to target ads more cleverly, although Facebook says that for now, data from Timeline apps is not used in that way.