Re: Views for denomalizing
Date: Sat, 05 Feb 2005 22:04:42 +0100
Message-ID: <67da011ciqa6vn90np3iblt0t7o7pi6vud_at_4ax.com>
On Fri, 4 Feb 2005 22:30:53 -0500, "Alan" <not.me_at_rcn.com> wrote:
>Yes it does. Tables are a physical implementation of a logical design.
No, tables are at the logical level.
The physical implementation of the table logical design are the internal structures used by the DBMS like BTrees, disk pages, bitmap indices, etc.
Views are as logical as tables.
>> But you can drop a view that is in a low normal form and to create new
>> views in 5NF.
>
>An instantiated view is a representation of data in one or more tables.
"Instantiated view" is a nonsensical term. A view is an special kind of table. It does not make sense to talk about "instantiated tables".
> The
>view itself has no normal form.
Why not?
A view is a derived table and it means that a view IS a table, and it has all the features of a table.
> It may present a representation of data in
>an NF other than that which that data is really stored.
Tables are logical constructions and how the data is really stored is part of the physical level.
The table logical structure might be very different to how the data is really stored (the physical level).
> It's kind of like lo
>oking at yourself in a fun house mirror and saying, boy, I sure lost a lot
>of weight. No, the mirror (view) only makes you look that way (5NF). It is
>not a representation of reality (3NF). In fact, it is a distortion of
>reality. The data is in 3NF, the view makes it appear to be in 5NF. But
>again, I think we basically agree and it's just a matter of semantics.
It is clear that you are confusing the logical and physical levels.
>> I meant that the ERD is at the conceptual level and the SQL database
>> design is at the logical level.
>
>We agree on this completely.
Then I don't understand you.You were saying that tables are physical constructs.
> I intentionally did not want to make that
>distinction in the original answer, as it just serves to confuse the issue
>at that point.
IMO that is exactly the contrary.
Regards Received on Sat Feb 05 2005 - 22:04:42 CET