Exercise 2/1
Are the following statements true or false?
In a Boolean retrieval system, stemming 
never lowers precision.
In a Boolean retrieval system, stemming 
never lowers recall.
Stemming increases the size of the 
vocabulary.
Stemming should be invoked at indexing 
time but not while processing a query.
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Exercise 2/5
Exercise 2/4
Exercise 2/9
The Term Vocabulary + Postings list (Chapter 2)
Below is a part of index with positions in the form
doc1: ⟨pos1, pos2, pos3, . . .⟩; doc2: ⟨pos1, pos2, . . .⟩; . . .
angels: 2 : ⟨36, 174, 252, 651⟩; 4 : ⟨12, 22, 102, 432⟩; 7 : ⟨17⟩;
fools: 2 : ⟨1, 17, 74, 222⟩; 4 : ⟨8, 78, 108, 458⟩; 7 : ⟨3, 13, 23, 193⟩;
fear: 2 : ⟨87, 704, 722, 901⟩; 4 : ⟨13, 43, 113, 433⟩; 7 : ⟨18, 328, 528⟩;
in: 2 : ⟨3, 37, 76, 444, 851⟩; 4 : ⟨10, 20, 110, 470, 500⟩; 7 : ⟨5, 15, 25, 195⟩;
rush: 2 : ⟨2, 66, 194, 321, 702⟩; 4 : ⟨9, 69, 149, 429, 569⟩; 7 : ⟨4, 14, 404⟩;
to: 2 : ⟨47, 86, 234, 999⟩; 4 : ⟨14, 24, 774, 944⟩; 7 : ⟨19, 319, 599, 709⟩;
tread: 2 : ⟨57, 94, 333⟩; 4 : ⟨15, 35, 155⟩; 7 : ⟨20, 320⟩; •
where: 2 : ⟨67, 124, 393, 1001⟩; 4 : ⟨11, 41, 101, 421, 431⟩; 7 : ⟨15, 35, 735⟩;
The following terms are phrase queries. Which documents correspond to the following 
queries and on which positions?
The index is incorrect. How? (hint: what properties must each index have?)
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Query1: fools          rush         in
Query2: fools rush in AND angels      fear      to      tread.
For the Porter stemmer group shown in 
Definition 3:
What is the purpose of including an 
identity rule such as SS → SS?
Applying just this rule group, what will 
the following words be stemmed to?: 
circus, canaries, boss
What rule should be added to correctly 
stem pony?
The stemming for pony and ponies might 
seem strange. Does it have a deleterious 
effect on retrieval? Why or why not?
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List the comparisons performed to intersect the 
following sorted non-positional postings lists with 
skip pointers of frequency 5.
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circus
canaries
boss P1 = [2, 10, 12, 16]
P2 = [1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]