INTO THE DEEP

摘要

With billions of web pages in their indexes, you might imagine that if something is online, search engines will find it for you. In reality, the vast majority of web pages are effectively invisible to them. Some of this "deep web" contains isolated pages with few, if any, hyperlinks, making them difficult to index. Much is stuff you wouldn't want to see anyway: web pages detailing old flight reservations, for example, or out-of-date product reviews on Amazon. However, a large proportion are believed to contain openly accessible databases of everything from information on used cars to the prices of airline seats.