Prior to this phase, subsystems which make the system have been defined. Requirements and verification tests for the subsystems are laid down. Functions for each of the subsystems are identified and suitable concepts have been selected in order to achieve these functions. In the development phase, these concepts are further refined, specifically for the system to be designed. Details regarding the realization of the system have to be finalized, in this phase.

==Flow Diagrams==

One of the ways to refine the concepts is to represent the functions to be achieved in terms of flow diagrams. This is explained by the following example. The electrical subsystem is responsible to ensure the supply of power to the system. For this example, let’s assume that uninterrupted supply of 1 A current is needed at 5 V. Generation and regulation of power are functions which are to be met by the electrical subsystem. This can be represented using the following schematic: <br/><br/>