Nine Algorithms That Changed the Future: The Ingenious Ideas That Drive Today's Computers

By John Maccormick | Go to book overview

2
Search Engine Indexing: Finding Needles in the
World’s Biggest Haystack

Now, Huck, where we’re a-standing you could touch that hole I got
out of with a fishing-pole. See if you can find it.

—MARK TWAIN, Tom Sawyer

Search engines have a profound effect on our lives. Most of us issue search queries many times a day, yet we rarely stop to wonder just how this remarkable tool can possibly work. The vast amount of information available and the speed and quality of the results have come to seem so normal that we actually get frustrated if a question can’t be answered within a few seconds. We tend to forget that every successful web search extracts a needle from the world’s largest haystack: the World Wide Web.

In fact, the superb service provided by search engines is not just the result of throwing a large amount of fancy technology at the problem. Yes, each of the major search engine companies runs an international network of enormous data centers, containing thousands of server computers and advanced networking equipment. But all of this hardware would be useless without the clever algorithms needed to organize and retrieve the information we request. So in this chapter and the one that follows, we’ll investigate some of the algorithmic gems that are put to work for us every time we do a web search. As we’ll soon see, two of the main tasks for a search engine are matching and ranking. This chapter covers a clever matching technique: the metaword trick. In the next chapter, we turn to the ranking task and examine Google’s celebrated PageRank algorithm.


MATCHING AND RANKING

It will be helpful to begin with a high-level view of what happens when you issue a web search query. As already mentioned, there

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