Re: No exceptions?
Date: Fri, 30 Jun 2006 00:22:25 GMT
paul c wrote:
> Bob Badour wrote:
>> paul c wrote: >> >>> J M Davitt wrote:
>>>> It almost seems as though you want to declare an analogue for DUM, >>>> syntax-check some expressions, and add attributes to your relation >>>> with the confidence that your expressions are still correct. >>> >>> Not exactly how I thought of it, but I think that's fair, after all, >>> one can add attributes, subject to one's external conception, to >>> relation definitions that don't have empty headings, in fact not that >>> the observation is of any use, that seems to be what happens when one >>> defines a relation with one attribute. >> >> I suggest an empty candidate key in a relation with any number of >> attributes is closer.
> I don't catch your drift. If we are on the same page, then trying to
> equate a relation that has either no rows or one row with a relation
> whose name is mis-spelled is indeterminate. If doing that is the same
> then I would have to give up on my original question.
You suggested that adding an attribute to a degree zero relation is a degree one relation. However, whether one adds one attribute or an arbitrary number of attributes is less important than the fact that the candidate key will have an empty set of attributes.
Basically, you have a choice: your compiler can stop with an error or your compiler can allow anything by replacing non-existent relvars with an arbitrary constant.
If one has a compiler that translates some user language into an internal language, one can catch most of the errors with it. Then, in the internal representation, once the compiler has established it is not an error, then it must be whatever it is. Received on Fri Jun 30 2006 - 02:22:25 CEST