[HCI] [Web] NYTimes on Next Generation of Web Apps
Interactions with many Web sites boil down to modern and extremely fast versions of an old and often slow process. If you go to a government office or a bank, for example, you fill out a form, hand it to the clerk or teller and eventually get something back. That is essentially the way most Web sites now work. You enter data on a Web page. You send that information to a distant computer, by pressing "Enter" or "Continue" or clicking a link. Eventually the computer sends something back. The page it sends is usually as static as a form you receive from a clerk. If you want to see something more - the next group of search results, other flights on different dates - you have to send another request and wait for another response.
At maps.google.com, pick the satellite view of any point in America. Then click on the map, and pan it east or west or use the right or left arrow keys for the same effect. With most mapping programs, when you reach the edge of the area initially displayed, you can't go any further without requesting and waiting for more data. With Google's map, you can head east or west - and keep going, all the way around the world, with the ability to zoom in at any point. The detail varies by country, but it is as if Google sent your computer a map of the globe's entire surface as soon as you logged on to its site.
Of course that's not what really happened. Instead, the system was applying two basic tricks to make it seem that you had an infinite map in your machine. One was asynchronous updating - that is, instead of waiting for you to request more data, it was preloading what it thought you might want next, at the edges of the current map. The other was very selective updating, altering only the parts of the display that had actually changed rather than bothering to "refresh" the whole page.
In general, he and others stressed that interacting with "rich" Web sites could become more and more like working at your own computer. For instance, Gmail, the Google e-mail service, now allows more sophisticated on-screen editing of its messages, and commerce sites can recalculate order totals and shipping costs instantly, as if they were spreadsheets. The key, again, is that pages are updated automatically, and only in the specific parts that have changed.