An Improved Feature Extraction Approach for Web Anomaly Detection Based on Semantic Structure

Algorithm 1

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(i)	Input: given a subgroup obtained by Section 5.1 and initialize as 1
(ii)	Output: a tree node for URLs in
(1)	Create a new node and extract parameter-value collection for a random URL
(2)	if, then
(3)	return the node
(4)	end if
(5)	extract for each URL in , and combine the value of ^th parameter into collection
(6)	calculate of
(7)	if, then
(8)
(9)	else
(10)	= {‘’}
(11)	end if
(12)	further split into several subgroups according to
(13)	for all subgroup do
(14)
(15)	add as a child of node
(16)	end for
(17)	return the node