From 2008762486148443616
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: f78e5,e94695845965b249
X-Google-Attributes: gidf78e5,public
X-Google-ArrivalTime: 1992-12-10 05:20:23 PST
Newsgroups: comp.std.c++
Path: sparky!uunet!mcsun!news.funet.fi!network.jyu.fi!sakkinen
From: sakkinen@jyu.fi (Markku Sakkinen)
Subject: Re: Zero-length structures and pointer comparisons
Message-ID: <1992Dec10.051649.10282@jyu.fi>
Organization: University of Jyvaskyla, Finland
References: <1992Dec8.143504.5590@jyu.fi> <5343@holden.lulea.trab.se>
Date: Thu, 10 Dec 1992 05:16:49 GMT
Lines: 37

In article <5343@holden.lulea.trab.se> jbn@lulea.trab.se (Johan Bengtsson) writes:
>Markku Sakkinen (sakkinen@jyu.fi) wrote:
>: ...
>: -- 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.

You must have misunderstood the idea somehow in two ways.
First, no matter how an object identifier is represented, it can always
be interpreted as an integer or bit string for the purpose of
ordering:  "violating the total ordering property" is impossible.

Second, the _identity_ of a persistent object in the database does not
change when the object is brought (or copied) to main memory.
The ordering is not supposed to be connected with the other
semantics of the objects, nor with their location in physical or
virtual memory (except as already dictated by the existing language
rules for array elements and class members, in C++).

----------------------------------------------------------------------
Markku Sakkinen (sakkinen@jytko.jyu.fi)
       SAKKINEN@FINJYU.bitnet (alternative network address)
Department of Computer Science and Information Systems
University of Jyvaskyla (a's with umlauts)
PL 35
SF-40351 Jyvaskyla (umlauts again)
Finland
----------------------------------------------------------------------