(25 marks) Consider the following ER-diagram and assumptions for a selling system. gname Group area Belong to sid Salesman pid name Sell Product pname cid Customer producer name Every group has a unique gname. Every salesman has a unique sid. Every customer has a unique cid. Every product has a unique pid. Every product can be uniquely identified by its pname and producer. A salesman belongs to exactly one group. A group contains at least one salesmen. A salesman can sell any number of products to a customer