A graphical system for executing a process or for programming a computer to execute the process is based on graphical programming techniques. Techniques include composing a graphical front panel of an instrument which provides a means for the user to provide input and monitor outputs of the process, composing a data flow diagram using graphical representations of data flow structures, and in response to the data flow diagram and the panel diagram, composing a sequence of execution instructions to carry out the diagrammed process in response to inputs provided by the panel to supply outputs displayed by the panel. The system is based on libraries of executable functions and variable types having corrresponding icons. The user selects icons which have corresponding entries in the libraries to assemble the diagrams. The system is responsive to the diagram to select the corresponding executable functions and variable types, and interconnecting the selected functions and data types to compose an executable program.