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From: mario@cs.man.ac.uk (Mario Wolczko)
Newsgroups: comp.object
Subject: Re: the need for classes as objects
Message-ID: <1650@m1.cs.man.ac.uk>
Date: 30 Aug 90 11:17:16 GMT
References: <2259@esquire.UUCP>
Sender: news@cs.man.ac.uk
Reply-To: mario@cs.man.ac.uk (Mario Wolczko)
Organization: University of Manchester
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Several posters have described applications in which the ability to
create classes at runtime made the applications simpler, cleaner, etc.
However, let me make a stronger, and perhaps more controversial claim.

I would suggest that IF you agree that the future direction for
object-oriented systems is to use persistent object stores as the
principal mechanism for long-term data storage, THEN inevitably
object-oriented systems will adopt not only classes as objects, but
also run-time creation and *even mutation* of classes and hence object
structure. 

My argument is based on the observation that it is impossible when
designing a class to foresee all the uses that instances of that class
may be put to, if those instances may exist for many years.  An
important property of a conventional database is the ability to
restructure the database to cope with change.  When we start
developing object stores with millions, possibly billions, of objects,
most of the value of these system will be in the objects, and not in
the "programs".  This is the case with large databases today:
application programs come and go; the data is always there.  In these
systems it will be essential to change the behaviour and even the
structure of objects as the system evolves, while preserving each
object's identity.

Only a handful of languages (such as Smalltalk) allow these sorts of
changes at all.  It seems to me that understanding how to manage this
kind of evolution is essential if we are ever to get widespread
acceptance of OODBs and persistent OOLs, but I don't see a lot of
activity in this area.

Mario Wolczko

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