DU-Rent is a company in car rental business (to see what "DU" stands for, fill the blanks in the following phrase "The Land __ __"). It has over 100 branches all over the country. It has about 5,000 cars and makes about 500,000 rentals per year. The rentals spread across 100 branches: branches in major airports, branches in major cities, and branches in local agencies such as hotels and garages. Each branch is identified by a branch number. DU-Rent has several IT systems. We are concerned with one of them. This system is called DU Rental System. Its main purpose is to maintain information of the cars and the rentals of those cars. It is also used to manage the car fleet, e.g. moving cars from branch to branch when necessary. It is decided that the system will be constructed as a central system which has access to the information about every DU-Rent branch. Later on, when it is installed at a branch, it will be customized to restrict its access scope to an appropriate level.