Thongprasit, P., S. Yuphong, and A. Poolkrajang. “The Development of a Soft Skills Model through Self-Learning for Front-Line Service Employees in service’s Business”. Journal of Humanities and Social Sciences Thonburi University, vol. 14, no. 2, May 2020, pp. 97-108, https://so03.tci-thaijo.org/index.php/trujournal/article/view/240392.