Functionality
Functionality is the essential purpose of any product or service. For certain items this is relatively easy to define, for example a ship's anchor has the function of holding a ship at a given location. The more functions a product has, e.g. an ATM machine, then the more complicated it becomes to define it's functionality. For software a list of functions can be specified, i.e. a sales order processing systems should be able to record customer information so that it can be used to reference a sales order. A sales order system should also provide the following functions:
Record sales order product, price and quantity.
Calculate total price.
Calculate appropriate sales tax.
Calculate date available to ship, based on inventory.
Generate purchase orders when stock falls below a given threshold.