Re: MV counterexample

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"Anthony W. Youngman" <wol_at_thewolery.demon.co.uk> wrote in message news:9+JYkXCOVVoAFwOc_at_thewolery.demon.co.uk...
> In message <40a11362$1_at_post.usenet.com>, x <x-false_at_yahoo.com> writes
> >> If we want to have user-defined datatypes like "age" or "sex", the user
> >> is going to have to be able to program (in some sense or other) the
> >> integrity checks, therefore integrity checking must be a user-space
> >> phenomenon. I just don't see how you can get round it. By definition,
> >> the database itself cannot use data to do primary integrity checks - it
> >> needs metadata. But the user can't provide metadata because the
database
> >> itself has no way of understanding it - it'll think it's data. Catch
22.
> >
> >Well, in the DKNF there are only two checks :
> >- domain membership
> >- keys enforcement
>
> What's DKNF? :-)
See http://www.almaden.ibm.com/cs/people/fagin/tods81.pdf

> >One of the problems the relational model is supposed to solve is :
> >"In contrast, the problems treated here are those of data
independence--the
> >independence of application programs and terminal activities from: GROWTH
in
> >data types"
> >:-)
>
> What does that mean? Seeing as I was responding to people who said that
> "you need user-defined primary data types to have a proper relational
> database", it sounds like you're saying the whole point of a relational
> database is to *restrict* datatypes in order to get a manageable system
> :-)

See http://www.scism.sbu.ac.uk/~rmkemp/codd1970.pdf ; last paragraph of first column of first page.

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