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 it is?”
One advisor, an engineer, answered first.
“It is a toaster” he said.
The king asked, “How would you design a computer for it?”
The engineer who was from a small private business replied, “Using a small microcontroller, I would write a simple program that reads the darkness knob and converts its position to one of 16 shades of darkness, from warmed up to burnt equivalent to the time the toaster would be on. Then it would turn on the heating elements and start the timer with the initial value selected via the knob. When the timer has counted down to zero, 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, an analyst from a big corporation which had loads of government contracts, 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 if 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 a full colour graphic logo appears on the screen. 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 the implementation phase. An ARM 9 processor running at 2Ghz with 32Gb of memory and a 1Tb hard disk 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. (Imagine the difficulty we would have had if we had foolishly allowed a hardware-first design strategy to lock us into a four-bit microcontroller!)”
The king wisely had the computer scientist beheaded, the large corporation barred from future government contracts and they all lived happily ever after.
From a common joke circulating the net since the year dot.