PageRank, the generally accepted metric of, among other things, how often a page is linked to, is only a small part of the larger story at Google. Talking to Google’s engineers and tracing the history of publicly announced search features, Levy discovers that a good deal of what Google has learned about search comes from the searchers themselves.
Take, for instance, the way Google’s engine learns which words are synonyms. “We discovered a nifty thing very early on,” Singhal says. “People change words in their queries. So someone would say, ‘pictures of dogs,’ and then they’d say, ‘pictures of puppies.’ So that told us that maybe ‘dogs’ and ‘puppies’ were interchangeable. We also learned that when you boil water, it’s hot water. We were relearning semantics from humans, and that was a great advance.”