Re: Another view on analysis and ER

On 7 dec, 12:17, Jon Heggland <jon.heggl..._at_ntnu.no> wrote:
> Quoth David BL:
>
> > I wasn't actually intending that Location be necessary for
> > identification of a marriage. I'll make the intensional definition
> > clearer:-
>
> > married(Husband, Wife, Location) :-
> > Husband is *currently* married to Wife
> > and they (last) got married at Location
>
> > Candidate keys are { Husband } or { Wife }, enforcing monogamy
> > integrity constraints.
>
> So Marriage is a relationship between a Husband and a Wife, yet it is
> identified by either, not the combination? I thought I finally had the
> common definition of "relationship" pegged, and then this comes along.
>
> I suppose I am looking for rigor where there is none, though. The
> definition of entity---something that is identified independently of
> other entities---is also rather half-baked. Take weak entities, for
> instance.

Allow me to make an attempt at a few definitions:

Entities are things.
Relationships are predicates.

What's wrong with this picture?

• Jan Hidders