4 User interface

In the analogy of televisions, the user interface is the remote control. To be more specific, the user interface is the collection of all the buttons on the remote control. In other words, a user interface defines what a consumer can do with a particular type of objects.

It is critical that a user interface be designed to be upward compatible in the future. Otherwise, a change of implementation (for better efficiency, reliability or security) may necessitate changes to a user interface. Any change to a user interface can potentially lead of a lot of changes to consumer code. The bottom line is that although a provider can make frequent changes to the implementation of a data type, the interface to the data type should only be changed in a backward compatible fashion.

A user interface should be published and well documented. This is because the user interface is the only source of information for a consumer regarding how a data type can be used.