Home -> Usenet -> comp.databases.theory -> Re: The Practical Benefits of the Relational Model

Re: The Practical Benefits of the Relational Model

From: Nathan Allan <nathan_at_alphora.com>
Date: 24 Sep 2002 18:19:12 -0700
Message-ID: <fedf3d42.0209241719.493e9969_at_posting.google.com> 






Here is a reply from C. J. Date.  Any typos are probably mine, not Mr.
Date's.


-Nate




Nathan Allan forwarded to me a message he had received from you, dated
September 4th, in which you made some slighting references to work by
Hugh Darwen and myself on type inheritance.  I would like to respond
to that message.  Text in quotes is taken verbatim from you original.



  "This is simply not true. There is no well defined and formal model


of 'type


inheritance' as part of the relational model. As you noted, relational
model is kind of orthogonal to types."



Well, it isn't clear, is it, what your opening "This" refers to. 
Nathan EXPLICITLY said that the relational model and types are
orthogonal (as you EXPLICITLY admit), and Darwen and I have EXPLICITLY
stated in our Third Manifesto book and elsewhere that "types are
orthogonal to tables" (see, e.g., the Third Manifesto book, 2nd
edition, page 21); so you can't be suggesting that Nathan or we are
claiming anything to the contrary; so that's not what you are stating
"is simply not true."  I have to conclude that what you think "is
simply not true" is that there is a "well defined and formal model of
type inheritance as part of the relational model."  But since you
agree that we agree with this statement, what exactly is it that you
think "is simply not true"?



  "Of course you're probably referring to Date&Darwen's proposal in


the Third


Manifesto, and is probably a value judgement to say whether that is
formal and well defined, but within a safe margin we can say it
doesn't meet the criteria."



I suppose that, in the final analysis, just about everything is a
value judgment, and everyone's entitled to his or her own opinions
(and values, come to that, within limits).  In the field of science,
however, it is generally accepted that we should strive for
commonality--even universality--of opinion as much as possible.  Thus,

to say, in effect, that in your personal opinion our proposal "doesn't
meet the criteria," without giving any indication as to what those
criteria might be, is not commentary worthy of a professional or a


scientist.  Especially when you qualify that opinion with the phrase
"within a safe margin"!  <bold>At the very least you should point to
specific parts of our proposal that you think are inadequate, and you
should then explain specifically why you hold such an opinion.</bold> 
Then we and others can judge your opinions on their merits.  As they
stand, your comments are unsubstantiated and unsupported, and to this
reader, at least, they appear just a trifle arrogant.  (And please
note that they would appear that way to me even if I were not one of
the injured parties.)



  "But first of all you're using bad terminology, it's not 'type


inheritance', it is _subtyping_. Subtyping and inheritance are
look-alikes but they should be treated distinctly.  Type inheritance
is the term Date&Darwen came up with after collecting almost all the
bad references from the OO literature ... and almost no good one ...
."



Part of the point here--as explicitly stated by Darwen and myself in
our Third Manifesto book and elsewhere--is precisely that there is no
consensus on the meanings of terms such as subtyping and type
inheritance.  PRECISELY because of this lack of consensus, we offer
our proposal as a contender for filling the gap (this fact too is
stated in the Third Manifesto book).  Thus, for you to state that our
proposal is "not 'type inheritance,' it is subtyping" is to beg the
question!  That is, your <i>opinion</i> relies on an <i>assumption</i>
that the terms "type inheritance" and subtyping" have universally
agreed meanings--which they manifestly do not.  Frankly, your position
here looks like an arrogant one again, at least to me.  As for your
assertion that "subtyping and inheritance ... should be treated
distinctly":  Well, that assertion might be valid, but it needs to be
substantiated.



Incidentally, I'd be interested (though not very) in learning how you
know that "Date&Darwen came up with" the term <i>type
inheritance</i>--regardless of whether or not we did so "after
collecting almost all the bad references from the OO literature .. and
almost no good one."  My own recollection (and I was there, and you
weren't) is that we didn't "come up with" the term at all.  Rather, we
were aware that the term was already being used out there in the
community, and we wanted to see if we could make any sense of it. 
Myself, I think we did--more sense, in fact, than I perceived in
certain portions of the literature.



  "To get an idea what is needed to present a formal and well defined


type system proposal, and all the issues a type system needs to
address  you might want to access some very good introductory book
available on the web" [specific references omitted here].



Maybe.  Personally, I think it would be more helpful in the context of
a commentary such as the one you were offering to Nathan to state some
specific criteria and to show specifically where our proposal falls
short with respect to those criteria.


Received on Wed Sep 25 2002 - 03:19:12 CEST












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