The structure of the application – User, Customer, Quotation, Quotations, Bill, and Bills

First, let's look at the structure of the application we're about to build. This is a sales management application built for the user to register customers, send quotations for orders, and finally to invoice the customer with a bill.

The user can input data in to the Customer table. The customer can be an individual or a company, either way, each customer receives a unique ID.

The Quotation table represents the final quotation sent to the customer. The Quotations table contains the individual items being ordered in the quotation.

A bill is the final invoice sent to the customer. As with the Quotations table, the Bills table refers to the individual items ordered by the customer.