Bob Badour wrote:
> Jon Heggland wrote:
>> vc wrote:
>>> My point is that if 'update' is shorthand for the respective relational
>>> assignment, then by the same token the update constraint must be
>>> shorthand for the respective relvar constraint: IS_EMPTY(R RENAME
>>> (Salary AS NewSalary) JOIN R' RENAME (Salary AS
>>> OldSalary) WHERE NewSalary < OldSalary).
>>
>> In that case, the shorthand is insufficient, because it doesn't specify
>> what you should join on. You could say it should join on the key by
>> default, but what if there's more than one key? What if you want keys to
>> be able to change?
>
> Natural join joins on all attributes with the same name. Given the
> rename operations specified, that would be every attribute except
> Salary. If one wanted to limit the join, one could rename additional
> attributes or project the relations onto the attributes of interest.
Not a bad idea, but you can't really apply it to Dataphor's TCs without
changing the syntax quite a bit by involving explicit renames and/or
projections. The resulting shorthand may not be all that short.
--
Jon
Received on Fri Sep 01 2006 - 14:43:45 CDT
