🚀 go-pugleaf

     In article <850@mtfmi.att.com> mel@mtfmi.att.com (M.HAAS) writes:
     Let's take one step back and see if there is a metaphor or analogy to
     what we are trying to do ...:

I believe that Mel Haas has asked a critical question that should be
re-examined.  There is much blind faith in the use of metaphor and
"consistent mental model" (I know, some of propogated by me), but
examination of actual systems and a wide variety of tasks doesn't seem
to show much consistent use in actual practice.

The Apple (Xerox Star?) desktop metaphor isn't realy one of a desktop.
If anything, it is of spatial locations, containers, and movements.
Double clicking to "launch" applications and cutting, pasting,
copying, and undoing are all invaluable, but don't fit the same
metaphor.   Moving the disk image into the trash can to ejectthe disk
is a violation that bothers many people at first usage, but seems
perfectly natural after just one or two uses.   The trash can example
is one that bothers me a lot (intellectually) because it illustates a
real violation of principle that causes no problems in practice.
(Some try to save it by redefining ejection of a diskette as a kind of
"throwing away" but I think this is a feeble save.)

I suspect that metaphors are useful in keeping consistency.  But
now Jonathan Grudin is about to present a paper in CHI 89 arguing about
the foolishness of consistency: systems are often improved by
violations.  Even the Lisa/Macintosh deliberately violated consistency
principles when user testing showed it was better to do so.

(One of my favorite examples comes from t he old Tenex operating
system (for the DEC PDP-10 and then 20) which kept multiple versions
of files around, file operation commands always operated on the latest
version: move, copy, rename, print, mail, edit.  One command, however,
was incosnistsent: delete got rid of the oldest, not the latest
version (thank goodness). So much for consistency.

Yes, early technoogy almost always copies older ones: early
automobiles had tillers, typewriter keys were arranged like piano
keyboards (some even had black and white keys), the first plastic
items for home and office tried hard to look like wood, etc.  But this
copying usually gives way to exploitation of the real power of the new
technology, which is not to copy.

If you examine the way people speak, there is heavy use of metaphor
(see Lakoff & Johnson's book, for example).  But the metaphors are
more often inconsistent and mixed than consistent, yet they cause
very little difficulty (except to professors and newspaper columnists
who love to cite them as perversities).

I do believe that we need overall consistency and a coherent mental
model (system image) so we can better remember and derive the
appropriate operations and better trouble shoot when things go wrong.
The Macintosh is superior in that it is easy to use most programs
without any manuals.  But most of this results from "visibility": I
can examine all the menu items and figure out what to do.  Some does
result from consistency in the use of editing commands and mouse
operations.  The main point is that we still understand this
suprisingly poorly.  Where consistency and mepaphor and consistent
system images-mental models help and where they hinder is not yet
properly understood.

Time for some more research, folks.

don norman

Donald A. Norman	[ danorman@ucsd.edu   BITNET: danorman@ucsd ]
Department of Cognitive Science C-015
University of California, San Diego
La Jolla, California 92093 USA
UNIX:  {gatech,rutgers,ucbvax,uunet}!ucsd!danorman
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