Help!~~~How to draw a class diagram of the system

A grocery store wants to automate its inventory.  It has point-of-sale terminals that can record all of the items and quantities that a customer purchases.  It has a similar terminal for the customer service desk to handle returns.  It has another terminal in the loading dock to handle arriving shipments from suppliers.  The fresh food department has terminals to enter losses/discounts due to spoilage.

谢谢哪位大哥能帮个忙画个UML的CLASS DIAGRAM，或者给点思路阿，能确定几个CLASS分别是什么~~~拜谢！