This is the phase that the developer discovers the structures needed to develop a system to meet the requirements from the analysis phase.

The design phase should not commit to early to writing code. However, in the case of an object oriented system, the output of the design phase should be a set of classes with the member functions declared and comments describing what they should do. These classes with their operations (member functions) should be sufficient to develop a system that meets the requirements.

The implementation of the functions is not specified and data members of classes are not required yet. So it is important that the comment for each member function clearly states what the function must do (but not how).

Member function stubs can be written that include the parameters and return type. However, the bodies will be left blank or return a default value in place of the actual implementation that comes in a later phase.