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From: jbn@lulea.trab.se (Johan Bengtsson)
Newsgroups: comp.std.c++
Subject: Re: Zero-length structures and pointer comparisons
Message-ID: <5343@holden.lulea.trab.se>
Date: 9 Dec 92 13:25:27 GMT
References: <1992Dec8.143504.5590@jyu.fi>
Organization: Telia Research AB, Aurorum 6, 951 75 Lulea, Sweden
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Markku Sakkinen (sakkinen@jyu.fi) wrote:
: In article <1992Dec07.225634.19943@microsoft.com> jimad@microsoft.com (Jim Adcock) writes:
: >|
: >|If the contents of some object are copied to or from the DB, that does not
: >|change or complicate the situation.  On the other hand, if some C++ object is deleted
: >|after having been copied to the DB, and the DB object is later restored into memory,
: >|it will be a _new_ C++ object.  
: >
: >What you suggest violates the fundamental tenents of OODBMSs -- namely that
: >an object maintains its identity no matter in what medium it is stored.

: -- as long as it is _in_ the database.  BTW, actually total order is
: a simple thing within an OODB _because_ the identity of each object
: is assured not to change.

It would impose severe restrictions on how the virtual address space
could be used though.  The OODBMS may end up in a situation where
it can't get a persistent object into memory, not because it has used up
all virtual memory addresses, but because all unused virtual memory
adresses would violate the total ordering property.

This unnecessary address space fragmentation phenomenon (kind of) would
severely limit the capacity of OODBMSes.

-- 
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