We study the problem of creating a functional design from a dataflow diagram D. We use the domination-relationship on data-items in D to obtain a canonical function calling-scheme S (D which is optimal in that it uses the minimum number of global variables for the interface among the functions, while keeping the function-parameters to a minimum. The difficulty in determining a function calling-scheme that is both valid and optimal comes from the fact that the number of valid calling-schemes is exponentially large in the size of D. We also use S (D to obtain a decomposition of D into larger single-output function-blocks. In [9 ],we give an algorithm to generate the basic pseudocode for each function, including its interface, for the calling-scheme S (D .