Here is the reference for the article
I read about versions in PIE:

A Layered Approach to Software Design
in Interactive Programming Environments
Barstow, Shrobe, Sandewall
McGraw Hill 1984

Previously published as CSL-80-5 December 1980
Xerox Palo Alto Research Center


-- 
+---Tom Morgan ------------------------------ (tmorgan at acm.org) -----+