Re: Objects and Relations

On Feb 6, 11:04 pm, "JOG" <j..._at_cs.nott.ac.uk> wrote:
> On Feb 6, 12:54 pm, "David BL" <davi..._at_iinet.net.au> wrote:
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> > On Feb 6, 7:26 pm, "JOG" <j..._at_cs.nott.ac.uk> wrote:
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> > > On Feb 6, 5:26 am, "David BL" <davi..._at_iinet.net.au> wrote:
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> > > > On Feb 6, 12:29 am, "JOG" <j..._at_cs.nott.ac.uk> wrote:
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> > > > > On Feb 5, 1:25 pm, "David BL" <davi..._at_iinet.net.au> wrote:
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> > > Discussion of OID's snipped because it appears we are in fact largely
> > > agreeing that all labels are attributes - and consequently that
> > > identity should not depend on a pointer or memory address, which is
> > > obviously not part of the real world data.
>
> > Good!
>
> > > > > > I agree that E/R modelling should be "consigned to being an
> > > > > > organizational tool", but again for different reasons. Unlike you I
> > > > > > see no problem with saying entities have identity.
>
> > > > > I have never said that. What I have argued is that they are identified
> > > > > by their attributes and not some imaginary hidden barcode.
>
> > > > I agree with that but don't see how that explains why E/R diagrams can
> > > > be problematic.
>
> > > This was an argument against OID's not E/R diagrams.
>
> > I hadn't realised you had a different argument against E/R diagrams.
>
> > > The argument against E/R diagrams is trying to define what an entity /
> > > is/. For example, if bob is married to shiela, is married_to a
> > > relationship or an entity? And if it is an associative entity, why are
> > > all relationships not then just entities? Or to put it a different way
> > > (and the way much of modern philosophy views knowledge) should all
> > > entities not just be viewed as n-ary relationships themselves? Once
> > > you arrive at this premise, by whatever route, whether it be data
> > > analysis, reductionism, etc, you are left with something that starts
> > > to look incredibly like NIAM/ORM, which in turn has a natural
> > > translation to relational modelling.
>
> > > > The claim that entities are illusionary or abstract
> > > > doesn't appeal to me.
>
> > > Fair enough. You are incorrect, but that would be a philosophical
> > > debate, and largely tangential to the practical issues at hand.
> > > However it is worth noting that your standpoint is that of
> > > essentialism, which carries little weight in modern epistimology.
>
> > My tendency these days is to believe that the universe (actually
> > multiverse) only exists in a Platonic sense and physical reality is a
> > kind of trick played on us as self-aware substructures of the
> > multiverse. That kind of kills the whole question of what is real
> > versus what is abstract. It seems more convenient to define
> > everything to be real (not abstract), whether they be humans or
> > numbers.
>
> > > So,
> > > perhaps instead you could clarify what you mean by an 'entity' and
> > > define exactly what it is, as a starter to convincing me that it is
> > > not in fact an abstract notion. (and please try and avoid using the
> > > word 'thing' in any such a definition).
>
> > Perhaps a more pertinent question is to ask you to define the
> > difference between real and abstract.
>
> > It's impossible to define entity in terms of simpler notions but I can
> > clarify my viewpoint.
>
> > If I point at a bunch of atoms and say "That is a human named Fred"
> > then I consider Fred to be conceptual, mathematically imprecise but
> > nevertheless the concept itself is real and exists in a Platonic sense
> > (to the extent that I can meaningfully make statements about that
> > bunch of atoms as I conceive of it as being a human named Fred).
>
> Well first pointing isn't allowed. One cannot continually follow Fred
> round pointing at him all day, we need to identify to him in some
> other way, but there I think we are agreed.
>
> However consider that some people's view of Fred is that Fred is Fred
> is Fred, throughout his whole lifetime. Other people/applications may
> need to view Fred only as he is /now/ - after all he will be composed
> of a completely different set of atoms in a few years anyway. Then
> there must be parts of him that make up our view of him which are
> purely abstract, his bravery, his humour, his IQ, his body of
> publications, etc., how should they perdure? Already the notion of
> where he starts and finishes as an 'entity' is seriously blurring.

That's why I said the mathematical concept of Fred is imprecise and can only be used meaningfully to the extent that we can state facts about Fred and not be confused.

If we could transplant body parts for example, then yes the imprecision in the mathematical concept is exposed.

> The old washington's axe/theseus ship paradox is perhaps a better
> example of the concept of a well defined entity being insufficient. I
> am sure you know it - "In a museum somewhere there is the axe used by
> washington. Ok, the handles been changed a few times. Oh and so has
> the headstock, but hey... its still the same axe". Same 'axe entity',
> completely different physical components. Something seems intuitively
> wrong with this notion of an axe 'entity/object'.

I feel it's worse if you're unwilling to say entities exist (even imprecisely) in any objective sense at all.

> But this problem is not really a paradox at all if you just discard
> the illusion that an entity exists anywhere outside a single
> individuals head.

I'm not entirely sure of your philosophy. Do you also say that more precise mathematical notions like the set of integers only exist in an individual's head?

> That's again why I believe one should always
> consider communicated propositions (which we have a shared common
> understanding of). Then you it becomes clear that the axe is the same
> axe if propositions discussing it use its name as the primary key. It
> is a different axe if the headstock/handle attributes are the compound
> key.

I can't help but think it's a little ridiculous to state facts about things and not believe those things exist in any objective sense. Do you also believe that the facts don't exist either?

This reminds me of the difference between realism and formalism. IMO formalism without realism is a strange viewpoint.

I note as well that Godel's theorems should not be interpreted as favoring formalism over realism. On the contrary I see it as revealing a limitation of formalism. In fact Godel himself was a Platonist.

> The purpose of this is not anal philosophising. Imo philosophy is
> absolutely pointless if it cannot be applied practically and
> usefully.

I see philosophy as only providing a context in which to communicate successfully.

> And in this Codd's approach is genius, because this entity-
> less philosophy underpins his original RM, and we've seen it actually /
> applies/ to solving real world data handling problems. Enough that it
> even seems possible to help me store information about employees _and_
> solve the Theseus Ship paradox in terms of RM keys. And unlike OO,
> simply from building on a firm mathematical foundation of predicate
> logic. Who'd have thought.

I believe my own criterion provides a simpler explanation of the difference between OO and RM and has nothing to do with one's philosophy.

> > As
> > a Platonist I don't like to say that the entity labelled Fred is
> > abstract. Instead I say it is real because I define all (reasonable)
> > mathematical notions to be real, whether they map back to atoms around
> > me or not. I say something physically exists if there is a mapping
> > back to atoms.
>
> Fair enough, but I don't really care if your a platonist, a
> reductionist, a mereological nihilist or a senior gynaecologist (and
> trust me compared to practicitioners like Gene and Marshall, I'm
> positively wooly). A philosophy is only worth its salt here if it has
> practical positive impact.
>
> > Entities are always real (ie exist) but they may or
> > may not physically exist. I note that the definition of physical
> > existence is dependent on the observer as a self-aware substructure in
> > a multiverse.
>
> So you object to me saying "entitities are abstract" by saying that
> because everything is abstract you are will deem them all "real". Then
> this is again just semantics.

That is my point. I stated that in the original post. I will quote...

    Consider a web server. This can be seen at a number     of different "levels of abstraction" [snip]     All of these "levels of abstraction" are equally valid.     I don't want to get into boring discussions about what's     physical versus logical, model versus what is modeled,     or real versus abstract

It is you that has made the claim that entities are illusionary and abstract and used that to make a point. By contrast I don't believe my argument depends on whether you consider entities to be abstract or real, objective or subjective. Received on Wed Feb 07 2007 - 04:01:28 CET