Pattarapantakul, T., and S. Kanchanasuwan. “Improving the Purchasing Process Using Lean Concept: The Case of Offshore Aviation Services Company”. WMS Journal of Management, vol. 9, no. 3, July 2020, pp. 90-101, https://so06.tci-thaijo.org/index.php/wms/article/view/243628.