Re: Why are [Database] Mathematicians Crippled ?

Op dinsdag 3 februari 2015 14:46:14 UTC+1 schreef Derek Asirvadem:
> Jan
>
> > On Tuesday, 3 February 2015 05:54:27 UTC+11, Jan Hidders wrote:
> > Op maandag 2 februari 2015 16:53:05 UTC+1 schreef Derek Asirvadem:
> > > > On Tuesday, 3 February 2015 02:10:09 UTC+11, Jan Hidders wrote:
> > > >
> > > > A correction: upon rematching the video I saw that he actually does give the definition in the beginning, even if somewhat briefly. He also refers to the lecture notes and mentions that they contain the full definition. So I withdraw my criticism.
> > >
> > > Ok.
> > >
> > > We are progressing very slowly.
> > >
> > > Now I realise, you probably did not understand my first post about this video.
> > >
> > > I know that he inflates the value of his knowledge, whatever he is going to teach, by mentioning databases that are in 1NF. I know that he gives the well-known theoretical "definition" for what is suggested as 3NF. But what you do not know is, that definition is the usual, stupid, fractured, fragmented, definition that is only relevant to theoreticians.
> > >
> > > It is only a fraction of the original Codd definition.
> >
> > Interesting. So what is his definition of 3NF and how does it differ from Codd's? Is it just different in wording, or is it actually not equivalent?
>
> That is difficult to express in your terms, because that process began just recently, and progress is slow, because there is no dictionary. And because the English doesn't work for you (I am sure that it is not a translation problem). Let me try anyway.
>
> 1. So you have the Codd definition, right ? Predates the donkey by decades; well-understood and accepted in the physical universe, etc. The 99%. Again, the unchanging law is, since you are not aware of it, since 1971, Codd's definition of Third Normal Form.
> ____ "Every non-key attribute is Functionally Dependent on the Key, the whole Key, and nothing but the Key"

Roughly, yes. This formulation is good as mnemonic device, but should not be confused with the real definition since it has several technical problems, But for the current discussion I think it's close enough.

> 2. You have the nutty professor, who gives:
> "<trigger fear response>
> <trigger self-importance>
> <trigger future security>
> Given a relation R{x-instance, y-instance}
> if they (whatever "they" means) agree on the x-attributes, then they /must/ agree on the y-attributes
> if that is the case then we say x functionally determines y"
>
> Do I have that correct ?

He doesn't restrict restrict the relation to the X attributes and Y attributes, but yes, his definition is that it holds for the rows in the relation that if they agree on the X attributes (the attributes in the set X) then they agree on the Y attributes.

> Good.

Yes. :-)  

> 3. So, using all your powers as a human, do you perceive any difference between [1] and [2] ?

Er .. well, yes. One is the definition of the concept of 3NF and the other of the concept of functional dependency. They *should* be different. So I'm not sure what you are trying to say here. I assumed you were busy showing that the same concepts are differently defined by Codd and Boetticher.

• Jan Hidders