Since this is a personal blog, I'd like to go a bit off-topic and take recognize my late mentor Gian-Carlo Rota, whose birthday is today. While I and countless others recall Gian-Carlo most fondly as a mentor and teacher, his crowning achievement was to make combinatorics a respectable branch of modern mathematics. Indeed, combinatorics and probability theory have been instrumental to the progress of information retrieval and information science.
And this nugget of his advice about lecturing seems remarkably appropriate in the context of how information retrieval engines should work:
Every lecture should state one main point and repeat it over and over, like a theme with variations. An audience is like a herd of cows, moving slowly in the direction they are being driven towards. If we make one point, we have a good chance that the audience will take the right direction; if we make several points, then the cows will scatter all over the field. The audience will lose interest and everyone will go back to the thoughts they interrupted in order to come to our lecture.Happy Birthday, Gian-Carlo.