Lee's Funnies

                                                     

Once upon a time, in a kingdom not far from here, a king 
summoned two of his advisors 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?"

One advisor, an engineer, answered first. "It is a toaster," 
he said. The king asked, "How would you design an embedded 
computer for it?" The engineer replied, "Using a four-bit 
microcontroller, I would write a simple program that reads 
the darkness knob and quantizes its position to one of 6 
shades of darkness, from snow white to coal black. The 
program would use that darkness level as an 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 advisor, a computer scientist, 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 omelette classes."

"The ham and cheese omelette 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 should click on it and the message 'Booting UNIX V. 
8.3' appears on the screen. (UNIX 8.3 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 32MB of memory, a 500MB hard disk and 
l7inch SVGA monitor should be sufficient. If you select a 
multi-tasking, object-oriented language that supports 
multiple inheritance and has a built-in GUI, writing the 
program will be a snap. (Imagine the difficulty we would 
have had if we had foolishly allowed a hardware-first design 
strategy to lock us into a four-bit microcontro11er~)"

The king wisely had the computer scientist beheaded, and 
they all (but the computer scientist) lived happily ever 
after.


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