1. A computer implemented method for programmatically affecting an attribute of a control in a data flow program in a computer system including a video screen, means for creating a graphical data flow diagram, and means for creating a panel associated with said data flow diagram for displaying data input to and output from said data flow diagram, the method comprising the computer implemented steps of: displaying on the screen a first panel; displaying on the screen a first control which displays data, wherein said first control is comprised in said first panel; displaying on the screen a first function icon that references a function icon control means for controlling a first function; displaying on the screen an attribute node icon associated with said first control, wherein the attribute node icon references an attribute control means for programmatically affecting an attribute of said first control; assembling on the screen a data flow diagram including the first function icon and the attribute node icon, wherein the first function icon is connected to the attribute node icon and wherein the function icon control means provides data to the attribute control means during execution of the data flow diagram, wherein said first panel is associated with said data flow diagram and wherein said first control in said first panel displays input or output data from said data flow diagram; executing the data flow diagram; the function icon control means writing a value to the attribute control means to affect said attribute of said first control during said step of executing; and changing said attribute of said first control after said step of the function icon control means writing said value to the attribute control means to affect said attribute of said first control.