1. A computer readable memory medium comprising program instructions for creating a graphical program, wherein the program instructions are executable to: display a function block in a graphical program, wherein the function block is operable to perform a first function, wherein the function block comprises one or more inputs and one or more outputs, and wherein the graphical program comprises a plurality of interconnected blocks which visually indicate the functionality of the graphical program; receive user input specifying an attribute behavior for the function block; and wherein the attribute behavior specified for the function block is usable to determine an attribute of at least a subset of the one or more outputs of the function block based on an attribute of at least one of the one or more inputs to the function block.