Retrieval Models
7.1 Overview of Retrieval Models
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7.1.1 Boolean Retrieval
TRUE FALSE AND OR NOT grep
president AND lincoln
NOT
president AND lincoln AND NOT (automobile OR car)
NOT
NOT(automobileORcar)
president AND lincoln AND biography AND life AND birthplace AND get- tysburg AND NOT (automobile OR car)
AND OR
president AND lincoln AND (biography OR life OR birthplace OR gettysburg) AND NOT (automobile OR car)
7.1.2 The Vector Space Model
t t Di
Di = (di1,di2,…,dit),
dij j n
Term1 Term2 … Termt Doc1 d11 d12 … d1t Doc2 d21 d22 … d2t
Docn dn1 dn2 … dnt
D3 (1,1,0,2,0,1,0,1,0,0,1)
Q t
Q = (q1,q2,…,qt),
qj j (0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1)
D1 Tropical Freshwater Aquarium Fish.
D2 Tropical Fish, Aquarium Care, Tank Setup.
D3 Keeping Tropical Fish and Goldfish in Aquariums,
and Fish Bowls.
D4 The Tropical Tank Homepage – Tropical Fish and
Aquariums.
D1 D2 D3 D4
aquarium 1111 bowl 0010 care 0100 fish 1121 freshwater 1000 goldfish 0010 homepage 0001 keep 0010 setup 0100 tank 0101 tropical 1112
t
Cosine(Di, Q) = j=1
D1 = (0.5, 0.8, 0.3) D2 = (0.9, 0.4, 0.2) Q = (1.5, 1.0, 0)
dij · qj j=1 j=1
Cosine(D1, Q) = (0.5 × 1.5) + (0.8 × 1.0) (0.52 + 0.82 + 0.32)(1.52 + 1.02)
= 1.55 = 0.87 (0.98 × 3.25)
Cosine(D2, Q) = (0.9 × 1.5) + (0.4 × 1.0) (0.92 + 0.42 + 0.22)(1.52 + 1.02)
= 1.75 = 0.97 (1.01 × 3.25)
Di
tfik k Di fik k
idf
idfk = nN k
idfk k N nk k idf
dik = ( (fik) + 1) · (N/nk)
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