Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!tektronix!tekcae!moiram
From: moiram@tekcae.CAX.TEK.COM (Moira Mallison)
Newsgroups: comp.databases
Subject: Re: relational vs object-oriented
Message-ID: <2514@tekcae.CAX.TEK.COM>
Date: 24 Feb 89 21:09:09 GMT
References: <376@uncmed.med.unc.edu> <3900005@m.cs.uiuc.edu>
Reply-To: moiram@tekcae.CAX.TEK.COM (Moira Mallison)
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 43
Fcc: outbox
Cc: moiram

Wrt Hal's question about extensibility of classes: yes and no!

While we have agreed that the object-oriented data model is
not clearly defined, I think you'd have a hard time convincing
both the database folks and the language folks that your model
was object-oriented  if it didn't have some facilities for 
extending the model by the user.

I have worked mostly with GemStone (*).  You cannot add methods
to any of the System Library classes, which only enforces good
programming practice: don't change a classes you haven't authored.
The problem is that you can't subclass off of certain system 
classes, either.  Integer is one of them (in fact, it might be
the super class, Number).  So when the operation I wanted 
wasn't in GemStone's methods, I had to punt.  What I did was 
put in a protocol for "utilities" for the object that held the
database and put my methods in there.  Then the message gets
sent to the database with an Integral argument, instead of
sending it to the Integer object directly.  

It works, but it feels kind of kludgey if you're used to 
Smalltalk.  And it's harder to share code, because general
kinds of operations (like random number generation) are
embedded in your database code, not in generic classes.
Note that this only applies to select System classes, not 
all of them.

I've worked with Vbase (**) somewhat less, and it has some
similar kinds of restrictions.  In any case, that product
is being re-architected and there may be changes to the
data model in Vbase+.

A third commercially available database is Gbase (***),
and I have not used it .

Moira Mallison
CAX Data Management
Tektronix, Inc.

(*)   GemStone is a product of Servio-Logic Corporation, Beaverton, OR.
(**)  Vbase is a product of Ontologic, Inc, Billerica, MA.  Vbase+ is
      in development.
(***) Gbase is a product of Graphael.