Md. Aminuddin, R., H. Jifeng, and R. Abdullah. “Specifying Concurrent Controller of Production Cell Using the Notation of Shared State and Events of Duration Calculus”. Malaysian Journal of Computer Science, vol. 14, no. 2, Dec. 2001, pp. 81-94, https://ejournal.um.edu.my/index.php/MJCS/article/view/5865.