Barack Obama has said we need a "Google for government." It's a nice line, but what does it mean? Federal agencies have been online since the mid-'90s. Obama's first crack at a Google-for-government law led to USAspending.gov, a budget tracker that looked like everything else the feds had put up on the Web--until I saw one geek-speak phrase on the home page, so small I almost missed it: API Documentation. To understand its significance, let me tell you how I got subway schedules on my iPhone.

Just a few days after Apple's iPhone launched, a trip planner for the San Francisco Bay Area's subway system, BART, appeared in the iTunes application store, which sells iPhone and iPod software for download. User reviews were mixed. But I was still floored. How could a local government agency move so quickly?

Turns out, it didn't. In 2007, Google engineers asked public-transit agencies across the country to submit their arrival and departure data in a simple, standard, open format--a text file, basically, with a bunch of numbers separated by commas--so Google Maps could generate bus and subway directions. A handful of agencies, including BART, decided to go a step further and publish that raw data online. Once they did that, any programmer could grab the data and write a trip planner, for any platform.

"It's not 1995," BART's Web-site manager, Timothy Moore, explained. "A single Web site is not the endgame anymore. People are planning trips on Google, they're using their iPhones. Because we opened up our schedule, we are in those places."

A couple weeks after that first BART application appeared, a new trip planner went live. This one, called iBART, was a thing of beauty. Free, too. It was written by two former high-school buddies--Ian Leighton, a sophomore at UC Berke­ley, and David Hodge, a sophomore at the University of Southern California. Forty thousand people downloaded the program in just a few weeks.

"We've created competition among developers," Moore said, "to see who can serve our customers best."

I met Moore and Leighton at a gathering in Silicon Valley called TransitCamp. Inspired by a similar event in Toronto, the idea was to brainstorm what you might do with transit-agency data. Nearly 100 people came. One guy was looking to build a Web site that combined an online ride-share forum with BART arrival and departure times. A pilot who runs an air-taxi business was hoping to mash up flight, bus, and subway schedules. Environmental activists were seeking new ways to get cars off the street.

What does any of this have to do with the federal budget? Well, USAspending.gov might look like any other government Web site, but its API--that's Application Programming Interface--allows access to the site's raw data in an open, standard file format, similar to a transit feed. ("Wow," Moore said. "That's really powerful.") Enterprising programmers, researchers, bloggers, or watchdogs like the Sunlight Foundation or Govtrack can grab that data and slice it, dice it, chart it, graph it, map it, or mash it up with new feeds.

It's not just the API that's a big deal, Greg Elin, Sunlight's chief data architect, told me. "It's the discipline an API imposes," he said. To build one, an agency has to record and store data in a way that anticipates public use. "Data sharing is no longer an afterthought," Elin explained. "You begin with the notion that you're going to share information. And you're going to make it easy for people." (Compare that with the approach of the Federal Communications Commission, which allows only limited searching of filings and comments; or that of the Department of Justice, which puts out data on foreign lobbying in unwieldy PDF format and binders.) An API also encourages the release of data in real time, instead of in occasional reports, like Federal Election Commission figures, or earmark spending.

Last September, Moore added a feed that broadcasts imminent train arrivals in real time. He's eager to see what people will do with it. "We can't envision every beneficial use for our data," Moore told me. "We don't have the time, we don't have the resources, and frankly, we don't have the vision. I'm sure there are people out there who have better ideas than we do. That's why we've opened it up."

We'd know a lot more about our government if Washington opened up the same way.