Re: Entity and Identity

From: Brian <brian_at_selzer-software.com>
Date: Mon, 3 Aug 2009 18:35:59 -0700 (PDT)
Message-ID: <40f45145-0645-40f2-ab9e-30c4a7c83c35_at_s31g2000yqs.googlegroups.com>


On Aug 3, 7:23 pm, rp_at_raampje.(none) (Reinier Post) wrote:
> Brian wrote:
> >On Jul 27, 7:24 pm, rp_at_raampje.(none) (Reinier Post) wrote:
> >> Brian wrote:
>
> >> [...]
> >> >It may be
> >> >splitting hairs, but there is a distinct difference between 'identity'
> >> >and 'the identity' in that 'identity' is a binary relation between
> >> >objects in the universe that denotes /is identical to/, but 'the
> >> >identity' of an object is that essential property (unary relation)
> >> >which distinguishes it from all other objects (its haecceity) and
> >> >which is embodied by an object identifier or by a proper name (in the
> >> >logical sense).
>
> >> I think this is utterly mistaken, regardless of whether you're referring
> >> to logic or to or OO programming.  Identity is never a relationship
> >> between objects, but between identifiers that denote (refer to) objects.
>
> >I suggest you bone up on Leibniz.
>
> That's a bit difficult, my Latin is extremely poor.
> But I think I've identified the source of this misunderstanding: page 146 of
> 'Relational database: selected writings' (Addison-Wesley 1989) by C. Date.
>

Unfortunately, I don't have access to that book.

> >> And haecceity is not a property.
>
> >Yes it is.  Is not the sum of all qualitative properties also a
> >property?
>
> It depends on what you mean by that.  The potential problem is not
> in considering a sum of properties as a property, but in the 'all'.
>
> If you define the haeccity of an entity type as the collection of all
> qualitative properties we distinguish for that object type, then of course
> haeccity can be regarded as a property of such objects. It just becomes
> another way of saying that all properties of a relation form a key.

I think we're talking across purposes. You seem to be saying that properties belong to an object type, when in fact they belong to the objects themselves. For example, 'being red' is a property, but is 'being red or being blue or being yellow' a property, or is it a predicate?

> I doubt this is what you mean.
>
> If you define it as all qualitative properties that can conceivably be
> distinguish for a particular object type, then you start running into
> circles: for every property you consider that adds distinctions between
> objects, you will need to decide whether the distinction is an essential
> characteristic of the object type itself, or of an object type that is
> related to the object type you're describing.  This is a modeling decision,
> not something that can be extracted from Mother Nature.
>
> --
> Reinier- Hide quoted text -
>
> - Show quoted text -
Received on Tue Aug 04 2009 - 03:35:59 CEST

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