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The world of database design will be explored, step by

step, in this 14-part series, Process-Driven Data Design.

by Frank Sweet

Have you ever noticed that there are just
two kinds of data entities in the real world?
Imagine, say, a 10,000-record vendor file
where, on average, 100 new vendors are
added each month and 100 inactive ones
purged. Its monthly volatility (turnover di-
vided by population) is 1%. Now consider
a file of 1,000 purchase orders where 1,000
orders are added each month and the same
number closed. Its volatility would be
100%.
Compute the volatility of the per-
;nanent files in your dp shop and you'll un-
cover something strange; there are two
populations out there—two classes of rec-
| ords. A histogram shows two peaks: one
i around 1% like our vendor example, the
i other near 100% like the purchase orders.
' Volatility is binary, it seems, and almost ev-
» ery record falls into one group or the other.
| Why is this? Does it apply to every data-
1 base? Does it reveal an important underly-
ing truth about data?

The answer to the last two guestions
is yes. But to find the why, we will journey
into the world of database design. We will
, see that objectively good designs exist, and
| we'il learn to recognize their traits. We'll
review eguations in data flow dynamics like
the above, and mnemonics like K <Du'.

<4 Ve'll manipulate the boxes and arrows of
7€ Jachman diagrams to derive, split, and

; ;nerge entities. We'll examine six useful de-
sign patterns we can apply to many appli-
cations. And we'll return with a checklist
that, applied to a design, tells us if it's ready
to be built.

In all, we'Il cover 14 topics in the

' next few months:

;? Durable, Doable Databases—the marks
of a sound design
» Data Flow Dynamics—the mathematics
of data movement

" »Objects and Events—the two populations

of records
% Keyfield Design —dataless, unigue, un-
rambiguous, unchanging

LESSON ONE:
DURABLE, DOABLE
DATABASES

F rank Sweet will show you the way to a leaner,
meaner, more flexible database

.

AUGUST 15, 1985 83