New research from the Hasso Plattner Institute in Potsdam, Germany, aims to quell the frustration and strife that can come when multiple people use a single touch screen. The project, called Bootstrapper, uses cameras below a table to identify different users by their shoes. Each set of shoes is linked to an account that keeps track of a person's actions and preferences.

Unlike other approaches to differentiating between users, Bootstrapper uses low-cost hardware and allows a person's hands to freely interact with the surface. As an added benefit, a user's preferences can be stored according to her shoes, so when she leaves the table, it's easier to resume an activity when she returns.

Previous approaches to the problem have involved affixing sensors to chairs, or using cameras positioned above a table. One approach required users to wear a ring that emits infrared, which was then tracked by the touch-table's cameras.

Patrick Baudisch, professor of computer science at the Hasso Plattner Institute, who developed the prototype system with graduate students Stephan Richter and Christian Holz, says shoes are ideal to track because they offer distinct features such as colors, seams, laces, logos, or stripes. They also typically maintain contact with the ground, unlike hands on a tabletop or bottoms in chairs, so they're easier to track.

Baudisch stresses that Bootstrapper is not intended as a security feature. "People can always spoof the system by buying the same shoes as someone else," he notes. The goal is to make collaboration easier and to log different people's usage over many sessions. The researchers, for example, used it to summarize users' achievements in a mathematics software program.

Bootstrapper collects video of shoes using cameras positioned below the surface of the table. Software extracts information about the texture of the shoe and links it with actions on the touch screen that correspond to hands and arms aligned with the shoes. With a small sample of 18 users and 18 different shoes, the researchers demonstrated that the system could recognize a user with 89 percent accuracy.

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.