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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: <5366@miramon.lulea.trab.se>
Date: 12 Dec 92 16:49:30 GMT
References: <1992Dec11.212831.19493@bcrka451.bnr.ca>
Organization: Telia Research AB, Aurorum 6, 951 75 Lulea, Sweden
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Stuart MacMartin (sjm@bcrki65.bnr.ca) wrote:
: In article jbn@lulea.trab.se (Johan Bengtsson) writes:
: >Put differently: the database ID total order and the corresponding
: >transient pointer orders must be order-isomorphic (look it up, I did :-),
: >to ensure that the total pointer order for the addresses of
: >persistent objects mapped into transient memory is consistent between
: >different runs of the same program.

: Aren't we talking about a total ordering that is consistent for the
: duration of the process?

Yes, primarily.

: The OODBMS objects can have an ordering that
: is persistent, but obviously the transient objects won't have a persistent
: ordering.  Do we care if the ordering of persistent objects is the same
: between different runs of the program?  Am I missing something?

A persistent structure that depends on total object ordering needs the
same ordering for all program runs.  As I think you pointed out in
another posting, the ordering need/should not be pointer based for OODBMSs
that use handle objects to refer to persistent objects.

Other OODBMSs that use straight pointers to refer to persistent
objects (e.g. ObjectStore,Texas) must provide a rather special
ptrcmp(void*,void*), or disallow use of ptrcmp() for persistent
objects (may be difficult to check).

-- 
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| Johan Bengtsson, Telia Research AB, Aurorum 6, S-951 75 Lulea, Sweden  |
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