Re: object algebra
Date: 3 Mar 2004 17:32:57 -0800
Message-ID: <4b45d3ad.0403031732.64596b12_at_posting.google.com>
> You're confusing missing information and nulls.
RDM creates NULLs when information required by a tuple is missing. Besides resorting to generic modelling, another solution is to mask NULLs with "disciplined default values" such as "Not Applicable". Similar to NULLs, masks for NULLs create "very serious ("showstopper") problem that it does not match reality - that is, results that are correct according to 3VL are sometimes incorrect in the real world". For example, the result might indicate that two persons have the same eyeColor because their eyeColors are both NA. According to my understanding of reality, this is incorrect. According to Marshall's understanding of reality, this is OK.
> Missing Information != NULL.
It is not possible to evaluate a statement with NULL with any certainty. Received on Thu Mar 04 2004 - 02:32:57 CET