Re: One-To-One Relationships

On Dec 1, 2:01 am, David BL <davi..._at_iinet.net.au> wrote:
> On Nov 30, 11:53 pm, JOG <j..._at_cs.nott.ac.uk> wrote:
>
>
>
> > On Nov 30, 3:41 am, David BL <davi..._at_iinet.net.au> wrote:
> > > 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:
> > > > > On Nov 30, 7:34 am, JOG <j..._at_cs.nott.ac.uk> wrote:
> > > > > > 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?
>
> > If everyone died who agreed to use that mapping, well of course, then
> > there is no pen, mug or keyboard constucts. Just a bunch of atoms with
> > no-one left to impose descriptions on them.
>
> There is no "of course" about it. A mathematical realist regards all
> mathematical constructs as having an independent existence. It cannot
> be proven true or false, hence its meta-physical status. I very much
> doubt whether you'll come up with any scientifically meaningful
> implications. You would be better served by regarding the question of
> existence as meaningless.

To be honest I take no stock in any form of realism. My understanding is that realism and empiricism are not popular concepts in philosophy these days in general, but I'm also aware that the field is subject to fashion just as much as any other ;)

>
> > > 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?
>
> > The problem is only if one views the bunch of atoms as one single pre-
> > defined thing. We're a lot more flexible than that. When one uses
> > entities in conversation one is incredibly adaptable with them and
> > their scope. When one encodes them in a data base its the opposite,
> > cementing a single, fixed and brittle viewpoint of the world. And that
> > will end up at best with query bias as requirements change, and at
> > worst a broken database.
>
> This is your non-uniqueness argument which is okay because it doesn't
> depend on metaphysics.

Then that is a good thing. All I want to see is a finely honed data model after all.

>
> > > > > > 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".
>
> > Agh, you're right. Apologies if I came across overly defensive - it is
> > very frustrating trying to describe what I see with clarity in my
> > noggin into cogent sentences. I was trying to get at the point that,
> > because entities don't exist as some a priori force of nature, that
> > they often aren't nice and neatly partitioned from other possible
> > entitiwa. Lots of nebulousness, overlap and change.
>
> You said "entities don't exist as some a priori force of nature". I
> think this statement mixes two different questions - the metaphysical
> one of existence, and the non-metaphysical one concerning
> uniqueness.
>
> I think it would be better to simply say "entities are constructs
> about the real world and are not uniquely defined", and thereby
> achieve your aim without triggering a philosophical debate.

I am starting to consider abandoning entities all together and just defining some other construct to start with. The whole topic appears to be an intractable minefield.

>
> > > > 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?
>
> > Off the top of my head I'd say a model centred on entities, uses them
> > as first order citizens through which to encode data (e.g. object-
> > orientation). Conversely, other models only reference entities
> > indirectly via statements about them (e.g. RM).
>
> I can see what you're saying, but I'm a little sceptical as to whether
> the distinction should be understood that way. To my mind, entities
> are outside the formalism whether based on RM or something akin to
> OO. As Paul suggested, you can't store an entity on a computer.
> Therefore technically entities are never first class citizens.
> What I mean is that in either case, you can talk about a mapping between
> entities in the real world and data structures on the computer.
> Furthermore, no one thinks that a person entity in the real world (a
> bunch of atoms) directly stores attributes like name and age.
> Therefore it is even reasonable to say that an OO approach is rather
> decoupled from reality.
>
> Despite all this, we agree that RM is generally far better suited for
> representing information about entities. I think your arguments are
> on the right track, but need some refinement!

Tell me about it. Everything is very fuzzy. Glimmers of clarity, washed away by a general sea of stodge. My head feels like a washing machine.

>
> > The former has a
> > single viewpoint of the partitioning of the universe of discourse, the
> > latter does not, allowing one to extract any particular conceptual
> > model from a neutral underlying logical model.
>
> I like this much more!
>
>
>
> > > > 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 non-
> > > uniqueness, which I find more agreeable than your previous meta-
> > > physical statements concerning existence.
>
> > It appears to be a natural consequence of following the line of logic
> > to me. Perhaps you can ellucidate though.
>
> Non-uniqueness is easy to understand, and you won't get much
> disagreement.
>
> Existence is metaphysical, and is orthogonal to uniqueness. You
> appear to be using the following "logic"
>
> not exist Platonically => not unique

Hmmm, I think I'm suggesting that because imo things don't exist platonically, and we impose form on the world, there are no nice neat encapsulations, and that the boundaries of entity types are wholly dependent on context. And that consequentially that impacts on good data modelling. I have no idea how to express that formally however, and I understand that as a realist you wouldn't agree anyhow ;)

I appreciate your comments. Regards, J.

>
> > > 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! :)
>
> > Me too ;) I don't really see anything wrong with E/R diagrams per se.
> > The problem is the lack of understanding that they represent only a /
> > single view/ of the universe of discourse. If one isn't aware of that,
> > well you can end up getting stuck down a one way road when new
> > requirements arrive.
Received on Sat Dec 01 2007 - 03:46:04 CET