Re: Relation Definition

Jan Hidders wrote:
> Dawn M. Wolthuis wrote:
> >
> > Is this one from Date the best in the industry?
>
> No. Of all the formal definitions of the relational model I have seen

> his is probably the clumsiest. For the authorative ones that real
> database theorists use see the definitions in the Alice book:
>
> http://portal.acm.org/citation.cfm?id=551350
>
> To summarize, when it is sufficient the "subset of cartesian product"

> definition is used, and when the names of the columns are relevant
for
> the discussion at hand the definition goes roughly something like the

> following:
>
> Def. [Tuple] A *tuple* is a partial function that maps column names
to
> domain values and is defined for a finite set of column names which
is
> called its *header*.
>
> Def. [Relation] A *relation* is a set of tuples that all have the
same
> header.
>
> There, that wasn't so hard now, was it? :-)

By no means - this is much improved! Do you mind if I add these to the glossary? I will have to read Alice.

I can guess what "domain" means here (a set), but would like that to be spelled out too at some point. There seem to be differences on what get tossed into the domain set -- does it have operators, for example?

I am very pleased to hear that one may simply use the mathematical definition of relation in database circles when column header names are not relevant, however, then I'm even more confused on why I get barked at when I use that definition. Ah well ...

Thanks once again for your help! --dawn
>
> -- Jan Hidders
Received on Fri Feb 18 2005 - 01:27:42 CET