Re: Two-valued logic

"--CELKO--" <joe.celko_at_northface.edu> wrote in message news:a264e7ea.0401030843.6b17ecd2_at_posting.google.com...
> >> However, I don't know if that is really the case or if I just
> happen to be reading the pro-two-valued logic folks. <<
>
> Yep, you are. The entire SQL world is on 3VL and if Cood had his way,
> it would be a 4VL (TRUE, FALSE, "attribute exists for the entity, but
> value not known" and "attribute does not exists for the entity, so
> value cannot exist")
>
> In fact, there is a whole area of "missing data" theory in the
> literature. Statistics have all kinds of "missing data" values, for
> example.

Thanks, yes good points. I have read the historic information and am well aware (too well aware!) of the 3VL of SQL since I have had to map a 2VL data store to it. Also, the issue of missing data is definitely swirled into this, along with the definition of a "NULL" value/no-value.

However, the more recent writings, including those of Date & Darwin IIRC indicate that a 2VL would be preferable. I agree that a 2VL is preferable, while still retaining a NULL value for missing data (treated as a null set so that it truely is a value).

--dawn Received on Sat Jan 03 2004 - 18:42:20 CET