Bibliografia
Systems modelling [En línia]. Available: http://www.open.edu/openlearn/science-maths-technology/computing-and-ict/systems-computer/systems-modelling/content-section-1. [Últim accés: 10 9 2013].
Systems modelling [En línia]. Available: http://www.open.edu/openlearn/science-maths-technology/computing-and-ict/systems-computer/systems-modelling/content-section-1. [Últim accés: 10 9 2013].