Re: Normalization and DBMS

• Post for FREE via your newsreader at post.usenet.com ****

"Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote in message news:c7rti3$m51$1_at_news.netins.net...
> "Leandro Guimarães Faria Corsetti Dutra" <leandro_at_dutra.fastmail.fm> wrote
> in message news:pan.2004.05.12.00.24.02.523801_at_dutra.fastmail.fm...
> > Em Tue, 11 May 2004 17:07:47 -0500, Dawn M. Wolthuis escreveu:
> >
> > > such constructs are much more likely in a relational
> > > database simply because there is no ability to have a "real" repeating
> > > group for the grades (a little subtable within the table).
> >
> > Consider that subtables add lots of complexity with no added power.
>
> I agree they add complexity of a sort and I agree there is no additional
> "power" but it seems to have a direct correlation to the flexibility of a
> system to withstand years of requirements changes. For example, if people
> used to have an e-mail address and now they have several, SOMETIME
> absolutely NOTHING has to change in the entire application other than to
> change the metadata for the field to describe it as permitting multiples.

You are right. SOMETIME.
Let's see for some operations if they are affected: 1) query the e-mail address: will return a set of addreses instead of one. Rule: When you ask for a value, always expect a set of values. 2) insert a new e-mail address: will add the address to the set. This is a kind of update in RM.
3) delete an e-mail address: will substract the address from the set. This is a kind of update in RM.
4) update the e-mail address: will forget all the addreses ? or it is equivalent to 3) then 2) ?.
5) equality test on e-mail address: will return a set of common e-mail addreses instead of true or false.
I'm concerned with the case 5) in this list. The questions are:
- How often this case will occur ?
- What logic we use to deal with this case ?

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

• Usenet.com - The #1 Usenet Newsgroup Service on The Planet! *** http://www.usenet.com Unlimited Download - 19 Seperate Servers - 90,000 groups - Uncensored -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=