Learning by analogy is a great way to illustrate
complex concepts, a tried and true teaching method used all over America.
Here are my notes on the benefits of teaching by analogy:
Also see my my notes on correlation vs. causation:
There are many examples of using analogy to teach Oracle,
this great analogy:
"Does the issue of the slowing of one read matter when
other process are being equally served at the same time? . . .
Consider passenger A and passenger B, both waiting to be served. To check in
each passenger takes five minutes, so passenger A is checked in in five
minutes and passenger B waits for five minutes then gets checked in and is
gone after a total wait of ten minutes.
If, in an effort to be equitable to both parties, the check-in agent flits
between the two then the total time to check them both in is now eleven
minutes (taking into account a total latency of one minute due to walking
between the desks), and they both wait the full eleven minutes to be
finished. Not equitable at all!"
Let's take a close look at fallacies of logic when using
Analogies and non sequiters
OTN discussion used several analogies that illustrate how analogies can be
misunderstood. To quote Oracle guru Steve Callan of Database Journal:
"The thing I hate most about tuning are all the lies,
especially the damn ones. The examples/case studies are more about
reinforcing the methodology/what to look for rather than having some hand
waving/"trust me it works" presentation.
For example, my car won't start. The engine turns over, but it won't start.
Me, the first thing I'm going to look at is how much gas I have left.
Maybe someone is going to suspect that the problem was
caused by his wife's boyfriend's wife's brother-in-law who bent a fuse in
the fuse box by 5 degrees and pasted some epoxy over one of the tips.
I'm sure that has happened, but more than likely,
you're out of gas. So, very common problems coupled with very common
Rube Goldberg played on this confusion in the early 21st
century with his hilariously over-complex implementations of common items.
Intermediate actions are irrelevant
The "Self-Operating Napkin" is activated when the soup
spoon (A) is raised to mouth, pulling string (B) and thereby jerking ladle
(C) which throws cracker (D) past parrot (E). Parrot jumps after cracker and
perch (F) tilts, upsetting seeds (G) into pail (H).
Extra weight in pail pulls cord (I), which opens and
lights automatic cigar lighter (J), setting off skyrocket (K) which causes
sickle (L) to cut string (M) and allow pendulum with attached napkin to
swing back and forth, thereby wiping chin.
After-dinner entertainment can be supplied with the
simple substitution of a harmonica for the napkin.
So, what can we say about the self-operating napkin?
1 - We have action "A" (raising the spoon)
2 - Action A results in reaction "M" (swinging napkin)
Are there intermediate actions? Plenty! Do they
make any difference in the cause-effect? No!
The fallacy of intermediate causation
It's not uncommon for beginners to misunderstand causation
and the net effect of of a action-reaction chain.
For example, if I know that there is a 70% chance that
people who bought Waldo's Widgets will also buy Cobb's Cogs, that's all we need
to know to launch a marketing campaign, targeting consumers of Waldo's Widgets.
But can analogies be misused and abused? Here is an
excellent example of an analogy that is intended to deceive:
Empirical Scientist. White lab coat. Clipboard. In lab. Table in lab. Glass
jar on table. A fly in the jar.
The scientist opens the jar, and places the fly on the table. He claps his
hand. The fly flies away. He notes on his clipboard, "The fly's hearing
He catches the fly. He tears off the wings from the poor fly and places it
on the table. Again he claps his hand. Puzzled, he claps his hands again. He
notes on his clipboard, "A fly cannot hear when it does not have wings!!".
He then writes, "Conclusion: The hearing organs of a fly is situated in
A conclusion based on observation only is idiotic."
Of course, this story is ludicrous because the conclusions
are not based on logic, but there are some people who infer that it has some
hidden meaning. In this case, the author says that conclusions based on
observations are idiotic.
In reality, the real moral is "A conclusion based on the
inference of intermediate causation is ridiculous (In this case, that the fly's
hearing caused it to fly away).
Read on to see what happens when people buy-in to this
faulty logic. Here we see a logic argument, well presented, unambiguous,
by itself, an excellent example of learning by analogy:
"Be careful about making conclusions using observation
only. Simple example. Observe how the WARP_SPEED hint makes the SQL go
So, lets decompose this statement with simple logic.