Re: Relational database comments

EscVector wrote:
> On Jun 8, 7:33 am, Serge Rielau <srie..._at_ca.ibm.com> wrote:
> > muddu wrote:
> > > One of the properties of a relation or table is that every row is
> > > unique. If this is so,
> > > what do we do with a table of comments?
> >
> > > Let's say, i want to put comments on a play in a relation. Two
> > > different people say
> > > "It was a great play". They both say exactly the same words. How
> > > can we put both comments
> > > in the relation if we must have uniqueness?
> >
> > If you want to preserve which person said what then the persons make the
> > row unique.
> > If you don't want to preserve which person said what, then there is
> > indeed no need for the extra row.
> >
> > Just my 2 cents
> > Cheers
> > Serge
>
> Comments are points in time. Comment 1 time a, comment 2 time b.
> It really depends on the app. If I say in my comment that a person
> requires a return call and that gets stored with no time or order
> reference, and another comment said called person, how do I know which
> came first. Does the called person refer to the first note or does
> the person require another call? I think the comment should have both
> time and key to know its origin.

I agree timestamps could be valuable, but doesn't it just move the problem to "What if two people make the same comment at the same time?" In practice an application might require some sort of user or session ID, then a more practical constraint becomes possible. Otherwise, I think the relational model is telling you that you need more information for both rows to be useful. Received on Sat Jun 09 2007 - 02:50:43 CDT