In a company database, details of the customers, the products sold and the orders made by customers are stored in the relations Customer, Product and Order, respectively: Customer Product pid pname county stock price cid c00 Jones c002 Smith c003 Green c004 Williams name county Essex Surrey Kent Kent p02 wood p03 ails p04 hammer p05 screws Sussex Kent Surrey Kent Essex 1114 0.50 2030 0.50 1.00 1.00 2214 1.00 1506 1253 Order ordno month cid pidquantity 1011 janc0 pol 1012 janc001 p2100 100 1019 feb c00 p04 40 1023 mar c001 p3 50 100 80 120 an 10261 may c002 p03 1015jan 04 1014jan p02120 1021 feb c04p100 2. One of the integrity rules of relational models is called referential integrity. (a) Explain what it refers to. (b) Using the given company database, discuss why it is desirable to enforce the referential integrity