H. P. Frei, D. L. Weller, R. Williams "A graphics-based programming-support system"

Phillips, Richard L. (1978) Phillips, Richard L. editor, Computer Graphics (SIGGRAPH 78 Conference Proceedings), volume 12, ACM SIGGRAPH, August 1978  

Languages mentioned Nassi-Shneiderman charts {1972} Graphical programming formalism