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Submitted on: 23 February 2004.
Revised on: 19 June 2004.
Accepted on: 18 July 2004.
___________________Journal of Grid Computing---SPRINGER
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Submitted on: 14 May 2009.
Revised on: 06 July 2009.
Accepted on: 19 July 2009.
___________________Journal of Grid Computing---SPRINGER
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