A method for generating function block diagrams with an interactive computer program using a functions data base is described. This step follows the generation of the requirements list, given in an earlier paper (Hundal and Byrne, 1989). The program prompts the user for system inputs and outputs, physical functions and their connectivity. Appropriate functions which may be used for realizing the function structure are suggested by the program. After the first function block diagram has been produced, variants can be generated by looking for alternatives for the chosen functions.