--- Peter Brawley <[EMAIL PROTECTED]>
wrote:
> >In the states table, should I list Colorado's
> regions
> >in three cells... Great Plains | Rocky Mountains |
> >Colorado Plateau, or group them in one cell, like
> >this:
>
> >Colorado | state | grasslands, Rocky Mountains,
> >Colorado Plateau | co | cna | 5
>
> >It gets even trickier, because I may link Colorado
> to
> >several regions, including ecological regions,
> >physiographic provinces and political.
>
> Codd's first axiom is that all values shall be
> atomic (yes, mysql sets &
> enums break that rule). Putting your little set
> 'grasslands, mountains,
> plateau' in one column would make queries on those
> items awkward. You might
> want to bone up on normalisation (viz links at
> http://www.artfulsoftware.com/dbresources.html).
Thanks for the link. I've been studying some of the
resources.
I have an idea for another approach. If putting
"grasslands, forests, mountains" in one cell is bad
practice, then I may wind up with a table with
hundreds of fields. Imagine one field filled with the
names of the world's nations. Then imagine another
field for tropical cloud forests, with three South
American nations checked. A few northern nations are
checked in the "Tundra" field, and so on.
Obviously, there are going to be vast numbers of cells
with no values at all.
But what if I instead created several tables, one for
each continent and listing only ecological regions
associated with that continent.
For example, the North America table might have just
three rows, for the U.S., Canada and Mexico, with the
following fields:
tundra | boreal forest | eastern forests | Rocky
Mountain forests | eastern grasslands | Great Plains |
Sonora desert | California coastal | Pacific Northwest
(there are actually a lot more.)
The Africa table would have far more rows, for nations
from Algeria to Zimbabwe, with fields that might look
something like this:
Sahara Desert | Sahel | Ethiopian mountains | tropical
forest | woodlands | savanna
Thus, North America and Africa will share no fields in
common. However, North America and Eurasia will both
share at least two fields - Tundra and Boreal Forest.
So, if I create such tables for each continent, will I
later be able to make a join that pulls up tundra in
North America, Eurasia and Antarctica? Can I pull up
the general term "grasslands" for all continents, or
pull up Great Plains grasslands for just North
America?
Thanks.
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