Re: Entity and Identity

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. And haecceity is not 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