Re: Entity and Identity

On Jul 27, 7:24 pm, rp_at_raampje.(none) (Reinier Post) wrote:
> Brian wrote:
>
> [...]
>
> >In the OO world, objects are instances of reference types.  The location
> >of an object can change over its lifetime, but what is used to
> >reference each object, the object identifier, doesn't.
>
> It depends on what you mean by that.
> Different identifiers can be used to point to the same object.
> That is a defining characteristic of objects.
>
> >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.

> And haecceity is not a property.

Yes it is. Is not the sum of all qualitative properties also a property?

> >The identity of an object is determined
> >(functionally) by its object identifier but can also be determined by
> >its current state in the same way that a relation schema can have more
> >than one key.  An object representing a particular serialized part can
> >be identified by its object identifier as well as by the part's serial
> >number, or by its position on the assembly line relative to all other
> >similar parts on the line, which could change over time (for example,
> >the part in front of it may have been scrapped).
>
> Here I agree with your point that objects can also be identified
> by other expressions than atomic identifiers.
>
> --
> Reinier
Received on Tue Jul 28 2009 - 04:06:13 CEST