http://www.theatlantic.com/technology/archive/2010/10/inside-the-google-books-algorithm/65422/
How the search algorithm works in Google Books
Rich Results is the latest in a series of smaller front-end tweaks that have been matched by backend improvements. Now, the book search algorithm takes into account more than 100 "signals," individual data categories that Google statistically integrates to rank your results. When you search for a book, Google Books doesn't just look at word frequency or how closely your query matches the title of a book. They now take into account web search frequency, recent book sales, the number of libraries that hold the title, and how often an older book has been reprinted.So, if you search "Help" now, you get a big blow-up of Kathryn Stockett's 2009 book, not one of the dozens of other books with the same title. Or if you search "dragon tattoo," you get Stieg Larsson's blockbuster, not the 2008 children's book actually called Dragon Tattoo.
"One of the fundamental things we've learned is that the whole is greater than the sum of the parts," Gray said.
This is deeply Google thinking but without the dominant algorithm. It's a Google subspecies that evolved by feeding on a different corpus. There is less data about books than web pages, but there is more structure to it, and there's less spam to contend with. Yet the focus on optimizing an experience from vast amounts of data remains. "You want it to have the standard Google quality as much as possible," Gray said. "[You want it to be] a merger of relevance and utility based on all these things."