Re: Weak entity types

From: David Cressey <>
Date: Fri, 17 Aug 2007 11:27:47 GMT
Message-ID: <TCfxi.3863$Be.597_at_trndny04>

"paul c" <> wrote in message news:f9bxi.66051$rX4.40692_at_pd7urf2no...

> Maybe I'm making the above exchange into more than it is but speaking of
> word choices and not to question my betters but I wish Codd had never
> used the term "model". It has so many connotations that are prey to
> willful twisting, such as "simulation" or even "emulation" that confuse
> the literalists, mystics as well as OO fans who dwell among minority
> rest of us into thinking that they can re-create reality in a machine.

I disagree completely. Back in 1970, Codd added clarity to a discipline that was needing more clarity. The use of the word "model" added clarity. The twisting of the word came along later. No matter what term Codd had used, people whould have twisted it, IMO.

The people who believed that some sort of graph based system of data was sufficient would have continued to believe that, with or without the word "model". See the great debate between Bachman and Codd. BTW, I do not include Bachman among the "weak minded" that you reference below.

> Also encourages the weak-minded to dream that just because there are
> mechanical ways that relations can be manipulated that there must be
> equally mechanical ways to define useful relations. The mathematical
> parallels that people come up with are useful but they remain
> abstractions by definition.

It takes a weak mind to fail to grasp that a model is inherently an abstraction.
If you build a 3 foot model of the Titanic, do the toilets flush?

> Plus they are extremely partial, for
> instance there doesn't seem to be an algebra that embodies persistence
> without resorting to using the word "persistence" and I suspect there
> couldn't be one. Sometimes I wish Codd had called his invention the
> relational abstraction, then it might have been more clear that there
> remains an irreducible element of Picasso's clever madness in all of
> this, especially when it comes to cutting out the crap.

BTW, Codd did not "invent" the relational model of data. He points out prior use of the relational model in the 1970 paper, IIRC. What was novel with Codd was the application of the relational model to the field of large scale data banks.

Quote from the 1970 paper:

"This paper is concerned with the application of elementary relation theory to systems which provide shared access to large banks of formatted data. Except for a paper by Childs [1], the principal application of relations to data systems has been to deductive question - answering systems. Levein and Maron [2] provide numerous references to work in this area.

In contrast, the problems treated here are those of data independence - the independence of application programs and terminal activities from growth in data types and changes in data representation and certain kinds of data inconsistency which are expected to become troublesome even in nondeductive systems.

The relational view (or model) of data described in Section 1 appears to be superior in several respects to the graph or network model [3, 4] presently in vogue for non-inferential systems. It provides a means of describing data with its natural structure only -- that is, without superimposing any additional structure for machine representation p[urp]oses. Accordingly, it provides a basis for a high level data language which will yield maximal independence between programs on the one hand and machine representation and organization of data on the other. "

The term "data independence" is also twisted by some object oriented people to mean the same thing as what they mean by "encapsulation". Although the two terms address parallel issues, they don't mean the same thing. Received on Fri Aug 17 2007 - 13:27:47 CEST

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