Mining User Generated Content

Social Annotation 41

in this node. At line 1, elements of P

0

are all initialized with 1, because

all tags are contained in the root node. From line 2 to 10, the algorithm

recursively splits each node until the termination condition is satisfied. We

finally gain a hierarchical structure and each node’s semantics is identified by

its corresponding leading tags.

Line 4 of Algorithm 1 is a key part of our model. The function f

D

serves as

a clustering machine. Input the node’s information, and f

D

outputs a series

of effective clusters derived from this node. Each cluster is described by the

value p(c

i

|t

j

) represents the relation between the jth tag and the ith