Combining Information from Multiple Internet Sources

3.3 Consensus method
The Consensus method was used previously in the AGWI system [1]. The Consensus
approach for conflict solving has been widely described by Nguyen N.T. in [4]. Its main aim is:
given a set of answers reach the common agreement on what the final combined answer should be.
It has been applied to be used in the application under considerations, however with slight
differences. The main assumptions of this approach were not altered – consensus answer is created
at the beginning and then its consistency is evaluated. The consistency part has been slightly
modified. One of steps performed in this algorithm is measuring of distances between result sets.
Modification changes the way; the evaluation of distances takes place. Another difference lies in the
method of choosing of the search engines for results retrieval. In the AGWI system there were more
search engines than there were Search Agents. In this case there are as many Search Agents as there
are search engines which are to be utilized.
First, the result sets are evaluated. A combined result set (without repetition of URLs) from
all result sets is created. Then for each URL its average position in result sets is calculated. After
that the combined result sets is sorted according to the average positions. The consensus answer is
found. Afterwards, it remains to check its consistency.
Listing 3.3.1 presents the pseudo code of algorithm for finding the consensus answer.
Input: Map of results
r 1, 2 ,...,
i
a ,
i i i i
= U U U n where U i , U
i
2 ,...,
U
i
n
result sets.
Output: Consensus answer
r
i
provided by m Search Agents – each in the form
1 are URLs. Map containing weights for
BEGIN
1. create setURLSfrom all URLs from all result sets (without
repetitions)
2. for each U ∈ URLS
-create array
( i)
r ;
t , t 2
,...,
t
1 n
where i
t is position on which U appears in
- if U does not appear in r
( i)
then set t i
as the length of the longest
ranking increased by 1
- divide each i
- calculate average ( U )
(i)
( i)
t by weight ( r ); if ( r ) = 0
t of values t 1
, t 2
,...,
tn
Listing 3.3.1 Consensus method main algorithm
33
weight divide by 0.01
3. consensus answer is obtained by ordering elements of URLSaccording
END
to values t ( U )