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Home -> Community -> Usenet -> comp.databases.theory -> Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

From: Jon Heggland <heggland_at_idi.ntnu.no>
Date: Fri, 17 Jun 2005 14:18:32 +0200
Message-ID: <MPG.1d1cde02f1adeda39896a2@news.ntnu.no>


In article <42b2ae72$1_at_news.fhg.de>, savinov_at_host.com says...
> > Ok, so it has some disadvantages. But how is it more reliable,
> > consistent and efficient? Previously, you have mostly talked about how
> > your model enables any query, no matter how vague or strange-looking, to
> > be answered.
>
> Ok, performance normally suffers as the level of organisation grows so I
> think simple databases will always be more efficient.

I agree. I like the RM in part for its simplicity. I'm not convinced that your model is simpler, or that it makes for simpler databases, though.

> But reliability and consistency increase because we loose our freedom to
> manipulate our data arbitrarily with no control (writing arbitrary SQL
> queries with unexpected or wrong result).

That is what constraints are for. See my other post for a discussion on unexpected or wrong results. (SQL can indeed produce logically incorrect results, but SQL is not relational.) This really is not a problem of the RM.

> All relationships become an
> integral part of the model and they are the primary focus of the
> database because they explain what our data mean. For example, if you do
> not need to write joins then will your queries more reliable (in the
> sense that you get that you really wanted)? I think yes.

If your pre-programmed join represents what I really want, yes. If not, no. Anyway, this can be done in the user interface and/or with views, without limiting the power of the underlying data model.

> >>Actually, the same high level goal is formulated for MS WinFS where they
> >>want all data items to be related
> >
> > Why should all data items be related? They are not necessarily related
> > in the real world; at least not in the subset of it we would want to
> > model using computers.
>
> If data items are not related then need to be modeled so.

I'm not able to interpret this. Do you mean that "unrelatedness" should also be modelled explicitly? Why?

In the RM, relationships/relatedness is indicated by the same value appearing more than once---"unrelatedness" is the compliment. How is this unsatisfactory?

> But if they are related then we need to have a model which can express
> these relationships.

And the RM can. I still don't see the problem. It seems to me that you are discarding many of the nice properties of the RM in order to achieve some other admittedly nice properties, that however are really easy to achieve in the RM as well, without sacrificing anything.

-- 
Jon
Received on Fri Jun 17 2005 - 07:18:32 CDT

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