Re: On formal HAS-A definition

On 7 mei, 01:38, r..._at_raampje.lan (Reinier Post) wrote:
> >On 4 mei, 23:21, Tegiri Nenashi <tegirinena..._at_gmail.com> wrote:
>
> >"Each customer has an address" can (and may likely) be modeled as two
> >distinct relvars, with an inclusion dependency / FK-like database
> >constraint / howyouwanttonameit between the two.
>
> This is neither aggregation (in the weak entity sense)
> nor composition (in the cardinality sense).

I think what this tells me is that it proves that in the real world, there exist certain kinds of has-a relationships that do not match any of those formal definitions you refer to, meaning in other words that those definitions are insufficient to model the real world.

> >As I already stated elsewhere, my feeling is that "is-a" and "has-a"
> >are part of the world of informal modeling, database constraints are
> >part of the world of formal modeling.
>
> They are not with my (e.g. Silberschatz et al.'s) definitions.
>
> >Those two worlds are disjoint,
> >and the only connection between them is that one (informal) may act as
> >the input for the designer who is deciding how to define the other.
>
> They are not disjoint at all.  They are both perfectly formalizable,
> one being more specific than the other.

Formalize what is informal and it is no longer informal.

Being less specific is precisely what I mean by "informal". Received on Fri May 07 2010 - 13:14:52 CEST