Re: The wisdom of the object mentors (Was: Searching OO Associations with RDBMS Persistence Models)

From: Dmitry A. Kazakov <>
Date: Thu, 1 Jun 2006 12:38:08 +0200
Message-ID: <1lrornqlsngid.1g1itr3c2tr04$>

On 1 Jun 2006 02:58:43 -0700, Erwin wrote:

>> It is strange to hear talks about identity from RM side. I thought RM
>> overcame that disease. There is no identity. Files are same, neither is
>> real. Paths aren't same. Identity is a relation, isn't it? Now if you'd
>> consider objects like (path,file), these could have identity defined as
>> id((path,file))=path.

> In the sense that "identity" refers to "the quality of being
> identical", there is of course nothing strange in the RM crowd using
> that term.
> Note that "being identical" requires two things, for else equality
> between them cannot be measured/observed/tested.
> Note further that the OO crowd always uses the term with respect to one
> single thing ("the identity of an object").

This is not true. As for identity of objects there are many of. For example, polymorphic objects have the identity of its specific type. The identity of objects in its usual sense is not required in OO. It is quite possible to have unidentifiable objects.

> The OO crowd thus never uses that term in the "relational" sense of the
> word.

I don't see much difference in respect of identity. The standpoint is that there is no data, only behavior. Data is expressed in observed behavior. So there is no immanent identity of values. There is only "=" relation defined on them (if any). The object is same as long as it exposes same behavior. Any question about what is inside is illegal.

Dmitry A. Kazakov
Received on Thu Jun 01 2006 - 12:38:08 CEST

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