Bags of words: the search engine

In this tutorial, I will explain the fundamentals of how current search engines work. The emphasis will not be on the engineering (although I will say a little about that), and not at all on business models of web search. Rather I will concentrate on the question of how search engines ever manage to find anything that you might possibly like to know about. You may be the kind of person who is impressed by their (let us say, G*****`s) astonishingly successful efforts; or you may be infuriated by their frequent total failure to read your mind. Either way, I hope to give you a little more insight into what you see.
I will also discuss how we got to the present situation, the current role(s) of search engines, and a little way into the future, including specifically why I think they are not going to go away for a little while yet.