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Aucbvax.1963 fa.works utzoo!duke!decvax!ucbvax!SHG@MIT-AI Sat Jun 27 10:00:08 1981 Interupting a workstation session I would like to comment on one part of Randy Ivanciw's letter about the need for an integrated environment for workstations. (Which I believe much of the world is coming around to endorsing even if they do not know how to do).

Randy gives the example where one is reading a mail inbox and gets a call on the phone. It would be very useful to be able to drop the mail, pick up the phone, answer the call, and then return to one's mail.

With iconographic systems (such as STAR or SMALLTALK-80) this would be quite simple. One would use the mouse to drag the cursor away from the current icon (be it editor window, mail inbox, virtual terminal) and position the cursor to the telephone icon. There one would expand the telephone icon and answer the phone. Later one could return to the old mail inbox icon.

However, there is a problem here that several Human Factor's people have pointed out. That is, one could easily have quite a few "pushed" windows, each one deep in some command dialog. The Human Factor's people have pointed out that humans have a real scarcity of short term memory (about 4-7 chunks). Clearly, we humans are going to have a real problem understanding what was going on in our workstations after a couple of interruptions.

Therefore, I would like to propogate, to designers of workstations, a user interface folk theorem that I heard recently: NEVER HAVE MULTIPLE LEVELS OF STATE ENCODED INTO A DISPLAY.

Naturally, I am curious as to what others feel this restriction will do to programming a user interface. I would also be interested in collecting other folk theorems.

- Steven Gutfreund

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