Path: utzoo!attcan!uunet!jarthur!usc!apple!apple.com!casseres
From: casseres@apple.com (David Casseres)
Newsgroups: comp.sys.mac.system
Subject: Re: The Mouse -- What is its History?
Message-ID: <10683@goofy.Apple.COM>
Date: 11 Oct 90 22:25:47 GMT
Sender: usenet@Apple.COM
Organization: Apple Computer, Inc.
Lines: 44
References:<21056@dime.cs.umass.edu> <1123@helens.Stanford.EDU> <9028@jarthur.Claremont.EDU> <1990Oct11.174840.21598@ux1.cso.uiuc.edu> <9038@jarthur.Claremont.EDU>

Since I brought up the question of what is the right number of buttons for 
a mouse, and the thread has now turned into a discussion of ways of using 
two or three buttons in a Mac or Mac-like interface, I thought maybe I 
should add a little perspective on Engelbart's three-button mouse.

Engelbart and his co-workers have not used the second and third buttons to 
enhance a one-button interface; rather, the 3-button design is an integral 
part of a completely non-Mac-like interface.

Very briefly, this interface is a thoroughly modal one, with the modes 
arranged in a tree of commands.  A set of one-character mnemonic commands 
put you in the mode you want:  for example if you want to delete a 
sequence of characters you would type DT for "delete text," then click 
with the rightmost button to select the first and last characters in the 
sequence.  A final click on the same button executes the command.  This 
button is called the "command accept" button or CA.

The center button is what makes the modal interface work well; it is the 
"command delete" or CD button.  What it does is walk backward through the 
command sequence from any point within it.  Suppose you have entered DT 
and clicked two characters, but you realize that the second click was 
wrong.  Click the center button and try again.  Or click the center button 
twice and do both character selections again.  Or click three times and 
you're back to the D for "delete," and now you can enter a W to delete a 
word instead.  Then you can do one click with the CA button on any 
character in the word you want to delete.

Feedback on the screen always lets you see where you are in the command 
structure.  The structure is both very logical, so it is learned readily, 
and very flexible, so it allows a rich set of commands.

The leftmost button is an auxiliary.  I am not sure what uses it currently 
has; when I was a user of this system, it was used as a shift-case in 
conjunction with another interface device, the 5-finger keyset for the 
left hand, used to enter short alphanumeric strings (such as the command 
mnemonics) without moving your hands onto the keyboard.

I have given this greatly oversimplified description in order to point out 
that three buttons permit the design of an interesting and powerful 
interface, but that interface does not resemble the Mac or any of its 
cousins.

David Casseres
     Exclaimer:  Hey!