Re: Another view on analysis and ER

On Dec 7, 4:04 pm, Jan Hidders <hidd..._at_gmail.com> wrote:
> 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:

Ah...ding! Now I understand why you were seemingly confused by the point of any discussion.

>
> Entities are things.
> Relationships are predicates.
>
> What's wrong with this picture?

Absolutely nothing! I don't see anything wrong whatsoever with that correspondence whatsoever. An entity is a thing, a thing is an entity. tick. A relationship is a predicate, a predicate is a relationship. check. But thats not really what I was enquiring about.

My question is when should one choose to represent (in FOL if one so desires) something as a thing, as in Exists x, or as a predicate, X(). So if I have my previous example "John from London married Jane from Manchester in a Church", do I have:

1. Married(Husband:John, Wife:Jane, Instituion:Church)
2. EXISTS! x E marriages [ Husband(x, John) ^ Wife(x, Jane) ^ Institution(x, Church) ]

First one is marriage as a predicate, the second one the marriage as a thing, x. Which to choose, and when. And if it depends ona certain application, does picking one not bind us into that single conceptual model?

However I see that all this entity/relationship nomenclature discussion has been a red herring. I have been a dope not to realize I could have stated the question via FOL without all this definitional hoopla. Your feedback is, as ever, appreciated. J.

>
> -- Jan Hidders
Received on Sat Dec 08 2007 - 21:37:41 CET