A telecommunication company provides telecom services and it wants to record the following

business information for better operation.

$$ Each customer can choose the company as their telecom carrier by themselves or be invited

by an existing customer, and an existing customer can refer many potential customers. Every

customer has a unique account number. Their name, address, telephone number, invitation

number are important information for the business operation.

$$ The company provides many programs for the customer to choose. The programs are

identified by their id$,$ type, duration and price. A customer has to join one and only one

program.

$$ The company also provides several promotions from time to time, customers are free to join

many of them but one at a time. The information of promotion id$,$ type, start date, end date,

price is very important information for both the company and the customers.

Please design a simplified data model for the company and help it better record the data for

business operations.