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Submitted on: 23 March 2008.
Revised on: 16 July 2008.
Accepted on: 14 August 2008.
___________________IT-Information Technology---WALTER DE GRUYTER GMBH
Submitted on: 27 November 2011.
Revised on: 27 February 2012.
Accepted on: 24 April 2012.
___________________IT-Information Technology---WALTER DE GRUYTER GMBH
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Submitted on: 30 October 2017.
Revised on: 29 January 2018.
Accepted on: 02 March 2018.
___________________IT-Information Technology---WALTER DE GRUYTER GMBH