Welcome to the Wiki page of the course Search Engines, WS 2009 / 2010. Lecturer: Hannah Bast. Tutorials: Marjan Celikik. Course web page: click here.

Here are PDFs of the slides of the lectures so far: Lecture 1, Lecture 2.

Here are PDFs of the exercise sheets so far: Exercise Sheet 1, Exercise Sheet 2.

Here are your solutions and comments on the previous exercise sheets: Exercise Sheet 1.

Here are the rules for the exercises as explained in Lecture 2.

Exercise Sheet 2

Here are the details about the three servers (UDP, TCP, HTTP) for Exercise 4:

All three servers are running on our machine vulcano.informatik.uni-freiburg.de (IP address is 132.230.152.135).

The UDP server is running on port 8888 of that machine. You can send it a number and it will then send you back that number of bytes, in packets of 1000 bytes each. (That means you also have to read packets of 1000 bytes each.) The first ten bytes of each packet contain the packet id. That is interesting for checking which packets get lost and in which order packets arrive.

The TCP server is running on port 9999 of that machine. You can send it a request of the form GET /<number of bytes> HTTP/1.1, or you can just use a downloading program like wget or curl and time it.

The HTTP server is running on port 80, as web servers normally do. Just download the file http://vulcano.informatik.uni-freiburg.de/file_100M and measure the time.

For measuring your transfer and error rates, as requested by the exercise, repeat your experiments several times and also at different times, and form the average of these measurements (or report several numbers if you get very different results). You should ask for large amounts of data, like 10 MB or 100 MB.

Here you can upload your solutions for Exercise Sheet 2.

Questions or comments below this line, most recent on top please

Hi Zhongjie + all, as it says above "The first ten bytes of each packet contain the packet id ...". (But it only does that if a packet is larger than 10 bytes.) For example, if you ask for 10000 bytes, the server will send you 10 packets with 1000 bytes each, with ids from 0 to 9. This is interesting information, because your client can use it to print the packet id of each package it receives and see how many packets arrive out of order. You don't have to do this for the exercise, but it's interesting and easy to do. And as you will see then, out of order arrival indeed happens. Hannah 1Nov09 2:07pm

Well, problem solved... You need to send a package end with a '\0' char to server, otherwise server will not respond... But here is another problem: when I send a UDP package like "5\0" to server, I will receive reply package like "xxxxx". If I send "10\0", the reply is "xxxxxxxxxx". And if it is "20\0" I send, it is "0000000000\0xxxxxxxxx" I receive. Confused... Zhongjie 1Nov09 11:20am

I had the same problem. But try to send your query with two linefeeds at the end, like this: send_data = '50\n\n' This makes the UDP server a lot more responsive... Christian 1Nov09 10:26am

hello Marjan, Now its work, thanks. what do you mean about skipping one ex.sheet without loosing any points? I wonder whether my exercise uploaded on 26 of Oct is still counted? Triatmoko 1Nov09 10:19

Hello! I still could not get any response from both the UDP and the TCP server port by now, but HTTP server works fine. If anyone could get some result, please tell me that you can get response from servers, so that I will know it's my own problem... Thank you! Zhongjie 1Nov09 08:43

Hi, I need some clarification on this term "HTTP result header" in Excercise 2 in sheet 2. Will HTTP header contains generic http information or something related to Results? Offcourse our Result will in HTML form. Waleed 1Nov09 5:52AM

I am sorry for the downtime, these maintenance works were announced already several weeks ago, but then I forgot about them because they were scheduled on a Saturday which I thought would not affect me. The downtime also killed our servers, but now they are running again. About the corrections: of course you should get comments on what you did wrong and why you got less points for what. Sorry, if that didn't happen for the first exercise sheet. I will talk with Marjan. Hannah 1Nov09 00:38am

Yes, Eric. Today afternoon and evening was nearly the whole Uni-Net Offline because of intended maintenance. I have a question: Will there be any correction or comments or a sample solution or something like that for every exercise because I now only know how many points I have for every Exercise in Exercise Sheet 1 but I don't know why I have a lack of 1/2 point in one exercise and in another. I think it would be good if anybody will know what he has done wrong or/and what he could have done better. Waldemar 31Oct09 21:08

I cannot connect to vulcano.informatik.uni-freiburg.de:9999 and :8888, neither from outside, nor from inside (logged into pool account). Also the whole informatik.uni... was down a few minutes ago. It's hard to solve exercise 4 without the servers running. Eric 31Oct09 19:00

Hi, I wonder whether those three servers for exercise 4 of sheet 2 online or not? Zhongjie 31Oct09 11:49

To all: Please note that (almost) everybody will get +2 points for Exercise Sheet 1 (previously I did not assign any points to the first and the last problem). Marjan 31Oct09 10:03

To Triatmoko and Ahmed + all: You obviously haven't created your wiki page. Please go to your link and click "Create a new page" and then "Save changes". You should then upload your solutions there and put the link on the wiki like everybody else did. If it is still not clear please ask some of your fellow students. I don't remember if it is mentioned, but you can skip one Exercise Sheet without losing any points. Marjan 31Oct09 09:38

Hi, I have some question about my exercise Sheet 1, I saw in my exercise page that my name, my upload solution and code in gray color and other persons in blue color. I try to click my attachment file in my exercise page, and I have some message that there are no attachment. any body know about this issue?because my exercise uploaded on Monday 26oct Triatmoko 30Oct09 22:18

Hi Björn + all: For Exercise 4 from Exercise Sheet 1 you had to write code that is at least able to process 2-word queries. If your code can indeed only handle 2-word queries and not an arbitrary number of query words, that is also fine for this exercise, you won't get less points because of that. Your second question is also very valid. You should put the various functionalities into modules / classes of their own, so that you can easily combine them for the three different binaries required for Exercises 1 - 3. Each of your three programs will then be quite short, just putting together the right things. I should have added it to my list of evil coding NoNos: never ever duplicate code, but instead put it in a class / module of its own. I hope this answers your questions, if not please ask again. Sorry for the late answer, but I was super busy until now, hardly had time to breathe. Hannah 30Oct09 19:08

I have a question concerning exercise 2. There was no concrete task to produce "query processing code" on ex sheet 1. Are there any requirements that have to be fulfilled? Should it be able to handle two word queries? n-word queries? Additionally there is something else I want to ask: I think it surely isn't bad practice to write a more generic webserver and use it for exercises 1-3. Apart from that it says "change your code" some times in the exercises. How should your submission behave w.r.t. the exercises? Different src files / executables for each exercise? One program that solve each exercises depending on startup parameters? Anything else? Björn 30ct09 2:25pm

I now reorganized the page. Old stuff went to separate pages (links above). The idea is that the front page is always for the current lecture / exercises. The problem with your exercise page should be solved now, Ivo. Hannah 30ct09 00:05am

Having problems to access my exercise page after loging in - IvoChichkovExercises, Ivo 29Oct 22:56pm

Sorry to bother you. I added the Link to exercise sheet 2 with the linked pdf. Needed this to find the sheet as fast as possible. Marius 29Oct 10:04 p.m.

Is there a webpage for exercise sheet 2 somewhere? Johannes 29Oct 07:45 pm