Re: Any new thoughts on OTLT (One True Lookup Table)

From: Laconic2 <laconic2_at_comcast.net>
Date: Sat, 27 Mar 2004 08:51:50 -0500
Message-ID: <VvydnVjPs7pEG_jdRVn-ug_at_comcast.com>


> Now, if you are designing a relational database, it's a really, really
> good idea never to put two values from different domains in the same
column.
> AFAIK, it's a requirement. If you put state codes and airline codes in
> separate columns, you might as well go ahead and put them in separate
> tables.

After I posted this, I realized that I was thinking like a database designer, and not like a mathematician. Regardless of what you put in a column, it's always possible to define a domain that encompasses all of the data in the column. So a mathematician would dismiss my point about not mixing different kinds of data in a single column as moot.

But, from my perspective, the question is whether the common domain "makes sense" to define or not. To me, the domain "state codes" can be explained to anyone who has ever addressed a letter by US snail mail. The domain "airline codes" can be explained to any travel agent, and to most passengers. But the domain "codes" only makes sense to a data processing wizard, not to a subject matter expert. It's a different level of abstraction.

So, back pedalling a bit, it's a really, really good idea, during data analysis, to define only those domains that clarify the analysis, rather than any domain that's mathematically possible. Whether you add more domain definitions at design time or not is beyond the scope of my discussion. Received on Sat Mar 27 2004 - 14:51:50 CET

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