Assume your company is developing a generic digital camera online purchasing system that can be sold to different camera stores. An initial analysis phase of the project has resulted in the following informal description of relevant data for the system. A store will be selling two types of products $-$ digital cameras and lenses. The digital cameras can have the following mutually exclusive optional features:

An ability to replace lenses.

Cameras with an electronic viewfinder.

Cameras with an optical viewfinder.

Cameras with an optical rangefinder.

Relevant properties of all cameras are the model number, retail price and the number currently in stock. Additionally, for cameras without the ability to replace lenses, there is a focal length range. Cameras with the ability to replace lenses are related to one or more lenses.

Properties of a lens that are relevant include the model number, retail price and the number currently in stock. Customers are either domestic customers or foreign customers. Properties of relevant customers include a unique customer number, a customer name, an email address and a shipping address.

Each customer may have any number of purchase orders. Each purchase order corresponds to one unit of any product at a time, either a camera or a lens, and will also have a selling price that may be different from the retail price of that item