Performance  Specifications'

When the background is understood,  and the goal  clearly  stated,  you  are ready  to  formu- late a set of performance specifications. These should not be design specifications. The difference  is that  performance  specifications  define  what  the system  must  do, while de- sign specifications define how it must do  it.  At  this  stage  of the  design  process  it is un- wise to attempt to specify  how  the  goal  is to be  accomplished.  That  is left  for  the  ide- ation   phase.    The  purpose   of  the  performance    specifications   is to  carefully   define and

constrain the problem so that it both can be solved  and can be shown  to have  been  solved after the fact. A sample  set  of performance  specifications  for  our  "grass  shortener"  is shown  in Table  1-2.

Note that these specifications constrain the design without  overly  restricting  the engineer's design freedom. It would be inappropriate to require a gasoline engine for specification 1, since other possibilities exist which will provide the  desired  mobility. Likewise, to demand stainless  steel  for  all  components  in  specification  2 would  be un- wise, since corrosion  resistance  can be obtained  by other,  less-expensive  means.  In  short, the  performance  specifications   serve  to define  the  problem   in as complete   and  as gener- al a manner as possible, and they serve as a contractual definition of what is to be ac- complished.    The  finished  design  can  be  tested  for  compliance   with  the specifications.

Ideation  and Invention

This  step  is full of both  fun  and  frustration.  This  phase  is potentially   the  most  satisfying  . to most designers, but it is also the most difficult. A great deal of research has been done to explore   the  phenomenon    of  "creativity."     It  is,  most  agree,  a  common   human   trait.  It      is certainly exhibited to a very high degree by all young children. The rate and degree of development that occurs in  the  human  from  birth  through  the  first  few  years  of life cer- tainly requires some innate creativity. Some have claimed  that  our methods  of  Western education tend to stifle children's  natural  creativity  by  encouraging  conformity  and re- stricting inpiduality. From "coloring within the lines" in kindergarten  to imitating  the textbook's writing patterns in later  grades,  inpiduality  is  suppressed  in  favor  of  a so- cializing  conformity.   This  is perhaps  necessary   to avoid  anarchy  but probably  does   have the effect  of reducing  the  inpidual's  ability  to  think  creatively.  Some  claim  that  cre- ativity can be  taught,  some  that  it is only  inherited.  No  hard  evidence  exists  for  either theory. It is probably true that one's lost or suppressed creativity  can be rekindled.  Oth-  er studies  suggest  that  most  everyone   underutilizes   his  or her potential   creative abilities.