1. Web Information retrieval (Web IR)
Handout #8:Probabilistic information retrieval
Ali Mohammad Zareh Bidoki
ECE Department, Yazd University
Autumn 2011

2. Outline
R(q,d)= P(d,|q)
Autumn 2011

3. Okapi BM25 Algorithm
f(qi,D) is the occurrences of qi in the document D
f(qi;Q) is the occurrences of qi in the query Q
|D| is the length of the document D (i.e., the number of words), and avgdl is the average document length
k1, k3 and b are free
parameters. Usually set k1 = 2.5, k3 = 0 and b = 0.8.
Autumn 2011