The toaster and the electrical engineer

Once upon a time, in a kingdom not far from here, a king summoned
two of his advisers for a test. He showed them both a shiny metal box
with two slots in the top, a control knob, and a lever.
"What do you think this is?" the King asked.

One adviser, an electrical engineer, answered first. "It is a
toaster," he said.

The king asked, "How would you design an embedded computer for it?"

The electrical engineer replied "Using a four-bit microcontroller, I would write a
simple program that reads the darkness knob and quantifies its position
to one of 16 shades of darkness, from snow white to coal black. The
program would use that darkness level as the index to a 16-element table
of initial timer values. Then it would turn on the heating elements
and start the timer with the initial value selected from the table.
At the end of the time delay, it would turn off the heat and pop up the
toast. Come back next week, and I'll show you a working prototype."

The second adviser, a software developer, immediately recognized
the danger of such short-sighted thinking. He said, "Toasters don't
just turn  bread into toast, they are also used to warm frozen
waffles.  What you see before you is really a breakfast food cooker.
As the subjects of your kingdom become more sophisticated, they will
demand more capabilities. They will need a breakfast food cooker that
can also cook sausage, fry bacon, and make scrambled eggs. A toaster
that only makes toast will soon be obsolete. If we don't look to the
future, we will have to completely redesign the toaster in just a few
years. With this in mind, we can formulate a more intelligent solution
to the problem. First, create a class of breakfast foods. Specialize
this class into subclasses: grains, pork, and poultry. The
specialization process should be repeated with grains divided into
toast, muffins, pancakes, and waffles; pork divided into sausage, links,
and bacon; and poultry divided into scrambled eggs, hard-boiled eggs,
poached eggs, fried eggs, and various omelet classes.  The ham and
cheese omelet class is worth special attention because it must
inherit characteristics from the pork, dairy, and poultry classes.
Thus, we see that the problem cannot be properly solved without
multiple inheritance. At run time, the program must create the proper
object and send a message to the object that says, 'Cook yourself.'
The semantics of this message depend, of course, on the kind of
object, so they have a different meaning to a piece of toast than to
scrambled eggs. Reviewing the process so far, we see that the
analysis phase has revealed that the primary requirement is to cook
any kind of breakfast food. In the design phase, we have discovered
some derived requirements. Specifically, we need an object-oriented
language with multiple inheritance. Of course, users don't want the
eggs to get cold while the bacon is frying, so concurrent processing
is required, too.  We must not forget the user interface. The lever
that lowers the food lacks versatility, and the darkness knob is
confusing. Users won't buy the product unless it has a user-friendly,
graphical interface. When the breakfast cooker is plugged in, users
should see a cowboy boot on the screen. Users click on it, and the
message 'Booting WindowsXX' appears on the screen.(WindowsXX
should be out by the time the product gets to the market.) Users
can pull down a menu and click on the foods they want to cook.
Having made the wise decision of specifying the software first
in the design phase, all that remains is to pick an adequate
hardware platform for the implementation phase. An Intel Pentium
with 2GB of memory, a 120GB hard disk, and a SVGA monitor should
be sufficient. If you select a multitasking, object oriented
language that supports multiple inheritance and has a built-in GUI,
writing the program will be a snap."

The king wisely had the software developer beheaded, and they
all lived happily ever after.


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This page contains a single entry by Paul Rako published on May 20, 2011 11:31 PM.

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