What's the difference between department stores and large supermarkets and shopping centers?

Department stores and large supermarkets sell basically the same kinds of goods. The difference is that department stores have counters to separate customers from goods, and they have to rely on salespeople to help them choose goods; And supermarkets are all self-help shopping. The difference between shopping centers and the above two is that shopping centers can have many businesses, but department stores and supermarkets are independent businesses.