Re: object algebra

> If Mary has no eyes, then the definition of a person as having eyes is
> flawed.

Since at design time, it is not possible to know the future, according to the above, in RDM a relation becomes flawed by the entry of a tuple that don't supply all the values. What if a tuple has an extra/new attribute? (In either case, this flaw doesn't occur with TDM)

> However, if it's convenient to require some designation for eye
> color, NULL is a lousy way to do it. You should in this case have an
> EYE_COLOR type, and one of its values could be "Not Applicable" or "Unknown"
> (both of which have well-defined meanings, unlike NULL).

NULL kills closure. How does substituting well-defined values such as "Not Applicable" or "Unknown, correct the problem?

Also now the domain/type EYE_COLOR has tuples "Not Applicable" or "Unknown". Doesn't this violate basic set theory?

Color = {red, green, blue} is valid.

Are you saying the following set is valid or allowed in RDM? Color = {Red, green, blue, "Not Applicable", "Unknown"}

Is "Not Applicable" a color? Received on Wed Feb 25 2004 - 07:01:39 CET