https://blog.gongquiz.com/2021/02/22/uml%ec%9d%98-%ea%b8%b0%eb%b3%b8-%ea%b5%ac%ec%84%b1%ec%9a%94%ec%86%8c%ea%b0%80-%ec%95%84%eb%8b%8c-%ea%b2%83%ec%9d%80-%ec%a0%95%eb%b3%b4%ec%b2%98%eb%a6%ac%ea%b8%b0%ec%82%ac-2020%eb%85%84-9%ec%9b%94/