Re: teaching relational basics to people, questions
Date: Mon, 23 Nov 2009 02:23:07 -0800 (PST)
Message-ID: <a004d4de-069f-445d-9f83-52b9f9ecd4b6_at_j11g2000vbi.googlegroups.com>
On Nov 22, 12:23 pm, vldm10 <vld..._at_yahoo.com> wrote:
> On Nov 16, 8:42 pm, Sampo Syreeni <de..._at_iki.fi> wrote:
> What is a purpose of 6NF if key is compound? I mean very compound.
> Vladimir Odrljin- Hide quoted text -
To illustrate above question I will give you the following example:
1.
R1{A,B,C,D} and KEY{A,B,C,D}.
My question is: What is an equivalent set of 6NF relvars for R1?
2.
Now we want to maintain changes of attributes. Then R1 become:
R1{A, StartDateA, EndDateA,…,EndDateD}
My question is: What is an equivalent set of 6NF relvars for R1?
3.Now I can add for example one more relvar: R2{A1, StartDateA1, EndDateA1,…, EndDateA10}.
4.
Now I have m-n relationship between R1 and R2. The relationship also
changes its attributes.
What is the key for this relationship
What is an equivalent set of 6NF relvars for this m-n relationship?
This is really simple example. There are dynamic db applications with
hundreds of relvars.
I can have an additional columns per one attribute. For examle in my
solution (see www.dbdesign11.com example 9) I have 6 additional
columns per one attribute.
For example I can insist that all date be in form YY, MM, DD, HH, MIN,
SEC – but I must take date as timestamp (technical reasons - in the
theory)
What will be 6NF equivalent for last m-n relationship?
Vladimir Odrljin Received on Mon Nov 23 2009 - 11:23:07 CET