This system may interface with one or more other external products, or be a component of a larger application. In this case, the product must be tested against the other interfaces it's communicating with or through. For instance, in a client server environment there may be interdependencies between one product and another that communicates through some other interface via the Internet. Also in a multi-tiered
environment the test team must take into consideration the interfaces between the client, middle tier and the back end. Each piece of the n-tiered
environment is integrated separately, tested separately and then tested again when all of the different pieces are integrated to make a complete operational system.