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Here are PDFs of the slides of the lectures so far: [[attachment:SearchEnginesWS0910/lecture-1.pdf|Lecture 1]], [[attachment:SearchEnginesWS0910/lecture-2.pdf|Lecture 2]], [[attachment:SearchEnginesWS0910/lecture-3.pdf|Lecture 3]], [[attachment:SearchEnginesWS0910/lecture-4.pdf|Lecture 4]]. | Here are PDFs of the slides of the lectures so far: [[attachment:SearchEnginesWS0910/lecture-1.pdf|Lecture 1]], [[attachment:SearchEnginesWS0910/lecture-2.pdf|Lecture 2]], [[attachment:SearchEnginesWS0910/lecture-3.pdf|Lecture 3]], [[attachment:SearchEnginesWS0910/lecture-4.pdf|Lecture 4]], [[attachment:SearchEnginesWS0910/lecture-5.pdf|Lecture 5]], [[attachment:SearchEnginesWS0910/lecture-6.pdf|Lecture 6]]. |
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Here are .lpd files of the recordings of the lectures so far (except Lecture 2, where we had problems with the microphone): [[http://vulcano.informatik.uni-freiburg.de/lecturnity/lecture-1.lpd|Lecture 1]] [[http://vulcano.informatik.uni-freiburg.de/lecturnity/lecture-3.lpd|Lecture 3]] [[http://vulcano.informatik.uni-freiburg.de/lecturnity/lecture-4.lpd|Lecture 4]]. | Here are .lpd files of the recordings of the lectures so far (except Lecture 2, where we had problems with the microphone): [[http://vulcano.informatik.uni-freiburg.de/lecturnity/lecture-1.lpd|Recording Lecture 1]], [[http://vulcano.informatik.uni-freiburg.de/lecturnity/lecture-3.lpd|Recording Lecture 3]], [[http://vulcano.informatik.uni-freiburg.de/lecturnity/lecture-4.lpd|Recording Lecture 4]], [[http://vulcano.informatik.uni-freiburg.de/lecturnity/lecture-5.lpd|Recording Lecture 5 (no audio)]], [[http://vulcano.informatik.uni-freiburg.de/lecturnity/lecture-6.lpd|Recording Lecture 6 (with audio for a change)]]. |
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Here are PDFs of the exercise sheets so far: [[attachment:SearchEnginesWS0910/exercise-1.pdf|Exercise Sheet 1]], [[attachment:SearchEnginesWS0910/exercise-2.pdf|Exercise Sheet 2]], [[attachment:SearchEnginesWS0910/exercise-3.pdf|Exercise Sheet 3]], [[attachment:SearchEnginesWS0910/exercise-4.pdf|Exercise Sheet 4]]. | Here are PDFs of the exercise sheets so far: [[attachment:SearchEnginesWS0910/exercise-1.pdf|Exercise Sheet 1]], [[attachment:SearchEnginesWS0910/exercise-2.pdf|Exercise Sheet 2]], [[attachment:SearchEnginesWS0910/exercise-3.pdf|Exercise Sheet 3]], [[attachment:SearchEnginesWS0910/exercise-4.pdf|Exercise Sheet 4]], [[attachment:SearchEnginesWS0910/exercise-5.pdf|Exercise Sheet 5]], [[attachment:SearchEnginesWS0910/exercise-6.pdf|Exercise Sheet 6]]. |
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Here are your solutions and comments on the previous exercise sheets: [[SearchEnginesWS0910/ExerciseSheet1|Solutions and Comments 1]], [[SearchEnginesWS0910/ExerciseSheet2|Solutions and Comments 2]], [[SearchEnginesWS0910/ExerciseSheet3|Solutions and Comments 3]] | Here are your solutions and comments on the previous exercise sheets: [[SearchEnginesWS0910/ExerciseSheet1|Solutions and Comments 1]], [[SearchEnginesWS0910/ExerciseSheet2|Solutions and Comments 2]], [[SearchEnginesWS0910/ExerciseSheet3|Solutions and Comments 3]], [[SearchEnginesWS0910/ExerciseSheet4|Solutions and Comments 4]], [[SearchEnginesWS0910/ExerciseSheet5|Solutions and Comments 5]]. |
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= Exercise Sheet 3 = | = Exercise Sheet 6 = |
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[[SearchEnginesWS0910/ExerciseSheet4|Here you can upload your solutions for Exercise Sheet 4]]. | [[SearchEnginesWS0910/ExerciseSheet6|Here you can upload your solutions for Exercise Sheet 6]]. |
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@Bit shifting: The syntax for that is actually the same, irrespectively of whether you use Java, C++, perl, python, or whatever. The >> operator shifts to the right, the << operator shifts to the left, the & operator ands the bits of the two operands and the | operator ors the bits of the two operands. Very simple. You will also find zillions of example programs on the web by typing something like ''java bit shifting'' into Google or whatever your favorite search engine is. '''Hannah 15Nov09 1:16''' | Hello, I wonder what's meant with the ratio demanded in exercise 1. If i have n lists with a maximum length of "a" and a total length of "b". Isn't the ratio something like "a:b"? At least that is what I thought. But adding a colon does not seem to be sufficient for a part of the exercise. Sorry for the meaningless question but I don't want to miss points because I'm not sure how to understand the word ratio. '''Björn 19:39''' |
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Hi Marius + all: For Exercise 4, an inverted list of size m with doc ids from the range [1..n] is simply a sorted list of m numbers from the range [1..n]. I leave it to you, whether your lists potentially contain duplicates (as in 3, 5, 5, 8, 12, ...) or whether you generate them in a way that they don't contain duplicates (as in 3, 5, 8, 17, ...). It doesn't really matter for the exercise whether your list has duplicated or not. In any case, consider simple flat lists like in the two examples I gave (and like all the examples I gave in this and past lectures), not lists of lists or anything. '''Hannah 15Nov09 1:12am''' | To all: about the selection of the ten prefixes. The idea was that you pick a meaningful variety by hand, that is, such prefixes which one could imagine that one would really type them. The exact selection doesn't really matter, but do avoid extreme cases like a prefix ''yzq'' with one completion and an inverted list of three doc ids. '''Hannah 29Nov09 6:28pm''' |
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@Mirko: Sure, but an inverted list is a list of words where the Doc-IDs are attached to each words in which the words occur. So for Example: If word no. 5 occurs in Doc1, Doc2 and Doc3 and word no. 2 occurs in Doc5, the list would look like: 5 -> Doc1, Doc2, Doc3; 2 -> Doc5. Or am I mistaken? My question then is, how long should these attached lists be in average case? I mean, one could imagine that we got 1mil. documents over 3 words, so these lists could get very large... | To Marius + all: yes, I am sorry, "cost" was very imprecise here, I actually simply meant the time your code takes. '''Hannah 29Nov09 6:19pm''' |
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EDIT: Oh ok. Now, I see your point. It's not an index, it's a list. Okay. So, what is an inverted list with Doc-IDs, then? | So you say that you mean by "costs" the running time? Or do you understand something else when you say we have to calculate the costs? '''Marius 11/29/09 4:58pm''' |
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EDIT EDIT: And to your question, Mirko, take a look at [[http://snippets.dzone.com/posts/show/93]]. Especially at Comment no. 2. Maybe this helps... I think, Java supports StreamWriters/Readers that are able to write/read bytes. '''Marius 11/14/2009 08:46pm''' | Notice about Problem 2: You should use precise timers when measuring the running times. If your collection is very small and you round up your times, it's easy to get 0 ms when merging or scanning the inverted lists. I recommend using microsecond scale. '''Marjan 29Nov09 16:47''' |
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EDIT EDIT EDIT: Sorry, me again. Well, I bothered Wikipedia which redirects from [[http://en.wikipedia.org/wiki/Inverted_list]] to Inverted Index. So it seems to me, this is being used as a synonym. Actually, I think I'm confused enough, now. I'll better wait for any responses... ;-) '''Marius 11/14/2009 9:08 pm''' | To Florian: Yes, you can do anything you want to find those words (as long as you produce the required outputs). '''Marjan 29Nov09 16:44''' |
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@ Marius: i think we are supposed to generate one inverted __list__ of size m, with doc ids from 1..n (therefore n>=m, because no duplicates?). | For exercise 1, should we use one of the methods presented in the lecture to find all words in the collection with the prefixes or can we do just anything to get them (though it might not be as efficient)? '''Florian 29Nov09 03:51pm''' |
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Now a question from my side: ex.4, programming the compression in __java__, is there any __good__ tutorial about how to handle the bit-stuff? (otherwise, i think, it would cost me too much time..) '''Mirko 14Nov09, 19:18''' | When you scan, please make sure that you do something very simple with the elements, like summing up all doc ids, and then outputting that sum. Otherwise a clever compiler might figure out that it can remove the whole loop, because it is not producing a result that is used anywhere. '''Hannah 28Nov09 11:48pm''' |
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Hi, do you have any suggestions what the best numbers for m and n in exercise 4 should look like? Or are we supposed to mess around a bit with ints and longs? And: How long should the list of documents in the inverted index be? '''Marius 14Nov09 6:40pm''' | To Mirko: Yes, scanning means one pass over the elements. '''Marjan 28Nov09 19:19''' |
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And just to clarify what a single-cycle permutation is. Here is an example for an array of size 5 with a permutation that is a single cycle: 5 4 1 3 2. Why single cycle? Well, A[1] = 5, A[5] = 2, A[2] = 4, A[4] = 3, A[3] = 1. (My indices in this example are 1,...,5 and not 0,...,4.) Here is an example of a permutation with three cycles: 2 1 4 3 5. The first cycle is A[1] = 2, A[2] =1. The second cycle is A[3] = 4, A[4] = 3. The third cycle is A[5] = 5. '''Hannah 12Nov09 8:04pm''' Hi Daniel + all, I don't quite understand your question and your example (if your array is 1 5 3 4 2, why is A[1] = 3?). In case you refer to the requirement of the exercise that the permutation consists only of a single cycle. That is because your code should go over each element exactly once (it should, of course, stop after n iterations, where n is the size of the array). If your permutation has more than one cycle, it is hard to achieve that. Also note that for both (1) and (2), the sum of the array values should be sum_i=1,...,n i = n * (n+1) / 2. '''Hannah 12Nov09 7:54pm''' Hi, I just looked at the new exercise sheet 4, in exercise 1 we should generate a permutation and sum the resulting array up, am I wrong or doesn't iterating method two iterate throw the whole array in every situation. for ex.: n= 5 permutation: 1 5 3 4 2, then A[1] = 3, A[A[1]]= A[3] = 1, A[1] = 3 ... '''Daniel 12Nov09 19:44pm''' |
Hi, about exercise2: is by "scanning" meant that one looks at every element exactly once? (=> costs of scanning a list are just the size of the list) '''Mirko 28Nov, 19:12''' |
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, Lecture 3, Lecture 4, Lecture 5, Lecture 6.
Here are .lpd files of the recordings of the lectures so far (except Lecture 2, where we had problems with the microphone): Recording Lecture 1, Recording Lecture 3, Recording Lecture 4, Recording Lecture 5 (no audio), Recording Lecture 6 (with audio for a change).
Here are PDFs of the exercise sheets so far: Exercise Sheet 1, Exercise Sheet 2, Exercise Sheet 3, Exercise Sheet 4, Exercise Sheet 5, Exercise Sheet 6.
Here are your solutions and comments on the previous exercise sheets: Solutions and Comments 1, Solutions and Comments 2, Solutions and Comments 3, Solutions and Comments 4, Solutions and Comments 5.
Exercise Sheet 6
The recordings of all lectures are now available, see above. Lecture 2 is missing because we had technical problems there. To play the recordings (it's .lpd files) you need the Lecturnity Player. You can download the player for free here.
Here are the rules for the exercises as explained in Lecture 2.
Here you can upload your solutions for Exercise Sheet 6.
Questions or comments below this line, most recent on top please
Hello, I wonder what's meant with the ratio demanded in exercise 1. If i have n lists with a maximum length of "a" and a total length of "b". Isn't the ratio something like "a:b"? At least that is what I thought. But adding a colon does not seem to be sufficient for a part of the exercise. Sorry for the meaningless question but I don't want to miss points because I'm not sure how to understand the word ratio. Björn 19:39
To all: about the selection of the ten prefixes. The idea was that you pick a meaningful variety by hand, that is, such prefixes which one could imagine that one would really type them. The exact selection doesn't really matter, but do avoid extreme cases like a prefix yzq with one completion and an inverted list of three doc ids. Hannah 29Nov09 6:28pm
To Marius + all: yes, I am sorry, "cost" was very imprecise here, I actually simply meant the time your code takes. Hannah 29Nov09 6:19pm
So you say that you mean by "costs" the running time? Or do you understand something else when you say we have to calculate the costs? Marius 11/29/09 4:58pm
Notice about Problem 2: You should use precise timers when measuring the running times. If your collection is very small and you round up your times, it's easy to get 0 ms when merging or scanning the inverted lists. I recommend using microsecond scale. Marjan 29Nov09 16:47
To Florian: Yes, you can do anything you want to find those words (as long as you produce the required outputs). Marjan 29Nov09 16:44
For exercise 1, should we use one of the methods presented in the lecture to find all words in the collection with the prefixes or can we do just anything to get them (though it might not be as efficient)? Florian 29Nov09 03:51pm
When you scan, please make sure that you do something very simple with the elements, like summing up all doc ids, and then outputting that sum. Otherwise a clever compiler might figure out that it can remove the whole loop, because it is not producing a result that is used anywhere. Hannah 28Nov09 11:48pm
To Mirko: Yes, scanning means one pass over the elements. Marjan 28Nov09 19:19
Hi, about exercise2: is by "scanning" meant that one looks at every element exactly once? (=> costs of scanning a list are just the size of the list) Mirko 28Nov, 19:12