How does Google do it?

How does Google do it? 

Well. There are times when you can argue about something and there are times when you just have to accept the job you’re given. I stared at the screen at the email from Our Esteemed Editor. It started off with ‘Can’t remember if I’ve ever suggested this before...’ and went on to ask about a particular algorithm. 

Ha! A ‘suggestion’, no less! Right! I can read between the lines as well as anyone, I didn’t get where I am today, etc. I dashed off a quick reply to the effect that my grandmother learned that algorithm whilst a teacher at Malory Towers (or was it The Chalet School?) and then secretly perused some algorithm books, sweat beading on the old brow. I brought up Google, which only made matters worse. How did they do it? 

Seriously, OEE had raised a thorny problem about whose solution I only had the vaguest idea. The question was that of text searching. How do Google and all the other web search engines enable you to find relevant web pages using only a couple of words? They can’t just download a billion pages and then search them all at your request. They must preprocess them and index them somehow. This article is about how they do this.

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