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Beata Czarnacka-Chrobot,  Factors of Effective Business Software Systems Development and Enhancement Projects Work Effort Estimation.   journal   = {International Journal of Social, Behavioral, Educational, Economic, Business and Industrial Engineering}, [online]. World Academy of Science, Engineering and Technology. January 2012, vol. 61(1). 39 - 46[viewed 22 September 2018]. Available from: http://waset.org/publications/4596.