Not all data comes into the system

Not all data comes into the system via a user interface. This is true for a particularly important class of e-business applications, business-to-business (B2B) e-commerce. Typically, B2B data comes into the system as a whole unit and is most likely to be expressed in XML. The B2B controller is responsible for parsing the message, verifying its correctness, and then requesting functions from the enterprise tier. A different B2B controller might be implemented for each different e-commerce activity that needs to be supported, or a controller might support several activities. It is important to notice that the B2B controller uses the same set of functions in the enterprise tier as the other access methods, such as a GUI. In other words, B2B represents a different entry point into the system using the same business functionality, not a separate application.