I would expand on that a analogy a bit, as a book index (like a database index) is not without cost. It takes up space in the book that now can't be used for th

I would expand on that a analogy a bit, as a book index (like a database index) is not without cost. It takes up space in the book that now can't be used for the actual text, it may not be useful for certain types of searches (i.e. the book index lists topics by title, but you're trying to find them by author, etc), and you have to keep the index up to date with later editions of the book (a topic inserted in the middle means you have to adjust the page numbers for a bunch of topics), etc. All in all though, I'd personally be pretty happy with that answer (I'm not the OP, though...)