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International Journal of Scientific and Research Publications, Volume 3, Issue 2, February 2013 325
ISSN 2250-3153
constructor of order k. An instance of the k order T is of the
form , where x 1 ,x 2 , . . . , x k are instances
of types T 1 , T 2 , . . . , Tk , respectively. The type T is called
1. A tuple, denoted by T , if the
cardinality (the number of instances) is 1
for every instantiation.
2. An option, denoted by (k )? T , if the
cardinality is either 0 or 1 for every
instantiation.
3. A set, denoted by {k} T , if the cardinality is
greater than 1 for some instantiation.
4. A disjunction, denoted by (T 1 | T 2 | . . . | Tk)
T, if all Ti (i=1,…..k) are options and the
cardinality sum of the k options((T 1 -Tk )
equals 1 for every instantiation
Figure 1 : (a) A web page (b),(c) It’s two different schemas
Definition 2: (Wrapper Induction)
Given a set of n DOM trees, created from some unknown
template T & values, deduce Template, schema & values from
set of DOM trees alone.
B. Methodology
Proposed approach detects schema of web pages by
constructing pattern tree. The process flow of system is as given
in figure below.
Figure 2 : Process flow of System
Proposed system consists of following steps :
Step 1: Take two web pages as input.
Step 2: For each page, we apply VIsion-based Page
Segmentation (VIPS) algorithm to segment Web page & to
build visual block tree.
Step 3: Blocks in visual trees of two web pages are compared to
detect fixed/variant template pages.
Step 4: For fixed template pages, we apply multiple tree merging
algorithm ,which consists of following steps.
• Peer Node Recognition :
• Matrix Alignment :
• Pattern Mining :
• Optional Node Merging :
Step 5 : We create pattern tree & schema is detected.
Step 6 : Data extraction is done by matching pattern tree & html
tree.
Step 7 : From variant template pages ,data is extracted.
C. Algorithms Used
1) VIPS Algorithm
For each input page, we apply VIPS [10] i.e. VIsion-based
Page Segmentation algorithm which is used to segment page into
block structure & then these visual block trees are compared to
check pages belong to fixed or variant template.
In VIsion-based Page Segmentation algorithm, the visionbased
content structure of a page is obtained by combining the
DOM structure and visual cues. For each page, we apply VIPS
[10] algorithm and visual block tree is constructed. Visual block
trees are compared, and on basis of position, size, color, font we
determine whether pages belong to fixed/variant template.
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