Re: One-To-One Relationships

On Nov 30, 10:53 am, JOG <j..._at_cs.nott.ac.uk> wrote:
> On Nov 30, 12:53 am, David BL <davi..._at_iinet.net.au> wrote:
>
>
>
>
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> > On Nov 30, 7:34 am, JOG <j..._at_cs.nott.ac.uk> wrote:
>
> > > On Nov 28, 10:37 pm, paul c <toledobythe..._at_ooyah.ac> wrote:
>
> > > > Bob Badour wrote:
> > > > > rpost wrote:
> > > > ...
> > > > >> This is the exact problem Chen identified. In the relational model
> > > > >> it is impossible to have entity-valued attributes, which, in practice,
> > > > >> we have a huge amount of.
>
> > > > > Entities are figments of our imaginations.
> > > > > ...
>
> > > > That's much better than my reply, looks like the essential point to me.
>
> > > Entities are concepts that we impose on that which is there (mostly
> > > shapes made out of atoms, but sometimes abstractions too).
>
> > > Entities are 'real' in that they are patterns that we think up and
> > > apply, and 'not real' in that if we were all dead, well there wouldn't
> > > be any 'entities' would there. Just atoms again.
>
> > Is this merely an argument against mathematical realism or something
> > more specific?
>
> I haven't argued anything, I have just defined entities. All seems
> like common sense to me.

Suppose I define a bijective mapping called "f" between the integers {1,2,3} and particular groups of atoms that I perceive right now on my desk as follows

    1 <--> {set of atoms that looks like a pen}
    2 <--> {set of atoms that looks like a mug}
    3 <--> {set of atoms that looks like a keyboard}

Does this mapping only exist in my mind, and would cease to exist if I died, or does the mapping have an independent existence? This is merely a philosophical question about mathematical realism. Or are you saying that the problem is in a precise definition of the groups of atoms?

> > > Because we conjure them up 'entities' aren't neatly defined, can
> > > overlap, change, and will differ from person to person. In fact its a
> > > testament to the amazing flexibilty of our noggins that that we
> > > manage to communicate at all.
>
> > Do you consider all mathematics to be "conjured up" and therefore not
> > neatly defined as well?
>
> Non-sequitur. I have made no comments on mathematics nor on anything
> being ill-defined.

You made the statement

    "Because we conjure them up 'entities' aren't neatly defined"

The use of the word "because" seems to suggest

    "conjured up" implies "not neatly defined".

> What I am suggesting is that given the contextual nature of how we
> define any given entity, any model centered upon them is going to have
> a very inflexible, brittle view of the world.

How do you distinguish between a model centered upon entities versus a model that is not?

> There are a load of atoms. Someone else looks at them and says hey its
> a dead bit of wood, its a 'stump' entity. Someone else considers a
> bigger picture and says its a snapshot of a 'tree' entity. Me, being
> lazy, say hey I could sit on that, its a 'seat' entity, etc., ad
> infinitum.
>
> Whos right? Noone. Everyone. Who cares. It just depends on the
> context, and with shared data, thats gonna vary. So lets encode the
> underlying bloody information, and not whatever brittle view of the
> world that first pops into our heads, ending up with a brittle,
> creaking database.

This appears to be a different argument to your previous one. I think you are now stating the underlying problem with entities is nonuniqueness,  which I find more agreeable than your previous metaphysical  statements concerning existence.

Or do you consider the non-uniqueness problem to only be a symptom of your meta-physical standpoint?

> > > And as such, anyone who tells you that you can build a permanent, all
> > > encompassing model out of such utterly woolly things is not to be
> > > trusted as far as you can throw them.
>
> > > P.S I have also had similar experinces at Ikea :) I don't follow the
> > > arrows anymore. They lie.
>
> > If there is a valid argument against "entities" I would hope it can be
> > stated more carefully than your or Bob's attempts.
>
> Again I haven't argued against entities. However, I am of course
> interested in what you deem invalid in my comments.

Yes, you argued against models that are centered around entities. However I don't actually know what that means.

Please don't take my post in the wrong way. I'm hoping the outcome will be a more accurate way of saying what's wrong with ER diagrams! :) Received on Fri Nov 30 2007 - 04:41:45 CET