Class 39: Slides [PPTX]

Sir Tim Berners-Lee, Information Management: A Proposal. 1989.

Sergey Brin and Lawrence Page, The Anatomy of a Large-Scale Hypertextual Web Search Engine.

Our main goal is to improve the quality of web search engines. In 1994, some people believed that a complete search index would make it possible to find anything easily. According to Best of the Web 1994 — Navigators, “The best navigation service should make it easy to find almost anything on the Web (once all the data is entered).” However, the Web of 1997 is quite different. Anyone who has used a search engine recently, can readily testify that the completeness of the index is not the only factor in the quality of search results. “Junk results” often wash out any results that a user is interested in. In fact, as of November 1997, only one of the top four commercial search engines finds itself (returns its own search page in response to its name in the top ten results). One of the main causes of this problem is that the number of documents in the indices has been increasing by many orders of magnitude, but the user’s ability to look at documents has not. People are still only willing to look at the first few tens of results. Because of this, as the collection size grows, we need tools that have very high precision (number of relevant documents returned, say in the top tens of results). Indeed, we want our notion of “relevant” to only include the very best documents since there may be tens of thousands of slightly relevant documents.

There is a bad mistake in the Question 6 of the exam!

The example shown in incorrect. The result should be:

> (define p (mlist 1 2 3 4 5))
> (make-cumulative! p)
> p
{1 3 6 10 15}

The value of each element in the result should be the sum of all elements in the original list up to and including that element. So, the first element in the output list is 1 = 1, the second is 1 + 2 = 3, the third is 1 + 2 + 3 = 6, the fourth is 1 + 2 + 3 + 4 = 10, and the fifth is 1 + 2 + 3 + 4 + 5 = 15.

Sorry for the confusion on this. You will receive full credit for this question if your answer either solves the problem as corrected here, or produces the same outputs as the example shown in the original exam.

Special thanks to Caroline Mattey for reporting the problem.

Class 38: Slides [PPTX], Notes [PDF]

J.C.R. Licklider and Robert W. Taylor, The Computer as a Communication Device, 1968.

Tim Berners-Lee: Answers for Young People

Sorry, I will not be able to hold my scheduled office hours today. I will have my office hours tomorrow (Tuesday, 11-noon). If that doesn’t work, please email me to arrange another time. (Kristina will still have her normal office hours in Davis Commons, noon-1:30 today.)

Everyone in the class should have received an email from the alonzo-bot that summarizes the grades recorded for you so far. If you did not receive this email, or found anything incorrect or confusing in it, please email me,

If you did the J option for PS8, this email should also contain comments on PS8. If you did the other option for PS8, you should have received an email from me in reply to your message.