Re: Lookup Tables, the right way?

michael_at_preece.net wrote:
> Frank Hamersley wrote:

>>michael_at_preece.net wrote:
>>>In the Pick environment you can use the Pick DBMS to persist data or
>>>you can use the host OS's file system - or any other physical media,
>>>including that accessible through a relational database. Sometimes it
>>>makes sense to organise data into a two-dimensional matrix with, say,
>>>columns represting one dimension and columns the other. Sometimes it
>>>doesn't. The designer is free to choose whichever model is most
>>>logical. A willingness to be constrained to a two-dimensional model is
>>>what we call adherence to the illogical model.
>>
>>What makes you so sure it (the RM to be explicit) is two-dimensional?
>>
>>Cheers, Frank.

Perhaps you shouldn't run on to the park if you fear an injury.

> Why do you need "nulls" to represent "missing values"? Isn't it because
> there can sometimes be no known value for a "cell", which we can think
> of as the intersection of a "column" (one dimension) and a "row"
> (t'other one)? In other words, every "n-dimensional tuple" (row) must
> have the same number of atomic values as every other "n-dimensional
> tuple" in the same table. Don't we then have a value to ascribe to "n"?
> Isn't "n" equal to the number of "columns"?

This para is really about another debate over nulls - suffice to say that the term "no known value" is a misnomer. The correct attribution of the role of null is either "no value" or "unknown value". In the first case the tuple can never ever have a value from the domain, and in the second case, there exists a domain value but we don't know what it is/was (at least at the moment).

Using 3VL causes these distinct meanings to become jumbled and indistinguishable leading to much gnashing of teeth by some. Because the complexity of 3VL is bad enough, moving to 4VL or nVL has never got close to pulling on a guernsey!

None of which affects the number of dimensions attributed to the RM.

Cheers, Frank. Received on Thu Mar 16 2006 - 02:53:55 CET