Re: On Formal IS-A definition

On May 5, 4:13 am, Tegiri Nenashi <tegirinena..._at_gmail.com> wrote:
> On May 3, 5:04 pm, paul c <toledobythe..._at_oohay.ac> wrote:
>
> > ... and never bring up,
> > say, just what the Information Principle really means.
>
> ..."the entire information content of the database is represented in
> one and only one way. Namely as explicit values in column positions
> (attributes) and rows in relations (tuples)."?
>
> It is obsolete.
>
> Seriously, I think it is aimed at cowboys who try to invent new data
> management systems without studying what relational model is about. It
> is about attributes and tuples because both relational calculus, and
> algebra explicitly refer to relations structured this way. The
> situation is similar to arithmetic where pupils learn how to add/
> multiply numbers represented in a very specific notation. So the
> arithmetic principle would say ..."the entire content of arithmetic is
> represented in one and only one way. Namely as explicit sequences of
> digits in numbers". Presumably arithmetic principle would prevent some
> from reinventing roman numerals:-)

I agree. My own take on the Information Principle is that "one and only one way" is misleading because one generally has a choice of whether to use rich or simple domain types. One could represent the entire database value in a single relation containing a single tuple with a single attribute and be adhering to the Information Principle. In that sense it seems rather vacuous.

In any case I think it's useful to have a label for when one only uses relations with simple data types (e.g. restricting oneself to integers, enums and strings), and perhaps using RVAs or TVAs. I have wondered whether that's the real intention behind the Information Principle. If so then it should be reworded, but then again I think many if not most people here would reject it anyway. Received on Wed May 05 2010 - 07:09:14 CEST