Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

Alexandr Savinov wrote:
> Tony Andrews schrieb:
> > Which part of the decomposition process reduces 1 row to 0 rows? I
> > must have missed that part...
>
> I'll try to exlain using another example (but I am not sure if it is
> necessary taking into account your apriori negative predisposition).

Sorry if my negative predisposition is so obvious. (I can't deny that I have it.) However, I will try to understand...

> This example is especially illustrative for those who absolutely trusts RM.
>
> How can you model a tree of items? There are two major alternatives:
> 1. Create a table with folders and a table with items. Each folder and
> each item has a field which specifies its parent folder.
> 2. Craate one table for each folder and store all items belonging to
> this folder in this table. There exist as many tables as we have folders.
>
> Conclusion: This example demonstrates that tables have the same semantic
> load as normal records, i.e., they should be treated not only as a
> structural element but also as means for representing data semantics.
> Addding/removing tables changes the model semantics rather than only its
> structure.

False: your alternative #2 does not represent the tree structure at all, it is just a bunch of unrelated tables, each of which contains some items. Where did the folder tree structure go? Try again! Received on Tue Jun 07 2005 - 13:32:34 CEST