Re: One-To-One Relationships

On Dec 2, 10:46 am, Jan Hidders <hidd..._at_gmail.com> wrote:
> On 1 dec, 01:13, JOG <j..._at_cs.nott.ac.uk> wrote:
>
> > On Nov 30, 9:36 pm, Jan Hidders <hidd..._at_gmail.com> wrote:
> > [snip]
>
> > > You want me to explain the difference between the notion of "thing"
> > > and "fact"?
>
> > Yet /again/ you are put new words in my mouth. I never mentioned the
> > word "fact" in this context. I asked you to elucidate the distinction
> > between 'entity' and 'relationship', following your condescending
> > statements (and *sigh*'s) that the issue has been resolved, inferring
> > that not just me, but everyone involved in the debate here was foolish
> > even to be discussing it.
>
> Hmm, you're reading a bit more into my sighs than I intended you
> to. :-)

Ah the joys of non-verbal communication. Perhaps I reacted too vociferously, so apologies for any over-defensiveness.

>I wasn't so much putting words into your mouth as telling you
> what I think the definition of entity and relationship are. An entity
> is just a thing, and a relationship is just a fact, or, to be bit more
> precise, an instantiated predicate. Wasn't that what you asked?
>

Yet I find those definitions entirely unsatisfying. Is a relationship not a 'thing' too? Its a noun after all. And how else can one possibly describe an entity apart from through 'facts'?

In addition the 'entity as thing' definition rather passes the buck as to defining what a 'thing' is. For a field exhibiting the rigour that mathematics does it all seems very hand wavy and fait accompli. It is possible that Deutch's logic of relative identity is attempting to solve all those identity puzzles after the horse has already bolted, and that there is something incomplete in our notion of entities that is generating the paradoxes. I just have this nagging feeling that there is something more subtle going on.

Either way, I also see nothing threatening to conceptual modelling on accepting the view of both entities and relationships as 'things'. If one views every relationship in E/R as an associative entity say, with its own attributes, well what would be lost? Surely nothing. And yet schema changes become simpler, translation to propositional models becomes easier, etc.

> > > You do realize that your response to Reinier also had that ingredient,
> > > don't you? Although others were far more worse. .
>
> > So others were far worse yet you jumped on mine, because of my
> > renowned impoliteness?
>
> No, because I thought you were an intelligent, polite enough and
> therefore interesting person to have a discussion with. If you would
> be notoriously impolite then the result would be just another flame
> war.
>
> > > I don't think so. The ER model places entities and relationships on
> > > equal footing. On the contrary, I would claim that the RM is
> > > unbalanced and focuses too much on the relationships.
>
> > You don't think I was talking about the best role for entities? What?
> > Indeed I was sir.
>
> The subject under discussion at the moment I replied was wether the
> distinction between the notion of Entity en Relationship is well-
> defined, useful et cetera. Reinier hasn't said or claimed that the
> best role should be for Entities.

Then it looks like we have crossed wires. My impression is that proponents of OO and E/R as a model unto itself, promote entities as first class citizens of a model, whereas RM proponents and logicians do not, utilizing them as second class citizens to be talked /about/. As Reiner appears to place himself in the E/R bracket I'd very much think he is claiming the former.

>
> > "Seems" to follow? I have said /numerous/ times recently that I
> > believe that entities are useful at the conceptual level, following
> > extraction from the logical model, and yet you now say I believe
> > "entities are no use for reasoning?"
>
> So you don't find the breakdown into entities and relationships a bad
> thing? If so, then I have misunderstood and offer my apologies.

Absolutely not. At the conceptual level I believe this is how most people think, and the model is their to facilitate them after all. I just believe there are numerous conceptual models, all equally valid, that can emerge from a neutral logical one, and I fear entityrelationship  thought as an end to itself can get one stuck in one brittle viewpoint (this is the same concern I have with XML).

>
> > > If the distinction is not useful and in
> > > fact bad for data modeling then this should somehow become apparent
> > > when you start working with such data models.
>
> > But it is very apparent Jan. A testament to that are the hundreds of
> > students I have encountered who end up very confused at the logical
> > layer because of it (and their pre-indoctrination in OO), dropping the
> > subject area as a result.
>
> Actually the problem is with OO is the same as with the RM, but at the
> other side of the spectrum. In OO the notion of entity is assumed to
> be central, in RM the notion of relationship is. Both are wrong.
>
> > > > Ought we just forgo all the /
> > > > ongoing/ issues in identity research, because FOL has its own
> > > > definition?
>
> > > Hm? FOL doesn't say much about identity. It just assumes you know how
> > > to tell which objects in the domain are the same or not.
>
> > FOL is based on Liebniz identity at its very heart, x = y -> AP [P(x)
> > <-> P(y)]. How is that saying nothing about the identity of entities?
>
> It simply posits the notion of identity and tells you what you can
> derive from it. It says nothing about where this identity relationship
> comes form or how it is established or that there may be different
> notions of identiy, et cetera.
>
> > And I still contend that questioning this notion of identity, and
> > hence the nature of entities, is worthy of discussion.
>
> Absolutely.
>
> -- Jan Hidders
Received on Sun Dec 02 2007 - 13:37:29 CET