Re: Views for denomalizing

On Fri, 4 Feb 2005 09:27:56 -0500, "Alan" <alan_at_erols.com> wrote:

>> >Views are a physical construction
>>
>> Very very wrong!
>
>Not at all. Proof: Show me a view that has no underlying tables.

Views have underlying tables by definition. Views are derived tables.

But it does not have any relationship with whether views are logical or physical.

>> Views are as logical as the rest of the relation variables.
>>
>> It seems that you are calling physical model to the logical model and
>> logical model to the conceptual model. This is a very common confusion
>> in the literature.
>
>I see. The literature is wrong and you are right.

Not exactly. An important part of the literature is wrong, but some books (the best) are right.

An example:

http://www.aw-bc.com/catalog/academic/product/0,4096,0321197844,00.html

>Almost. A view is made of normalized or non-normalized tables. It can be
>determined if the resulting view is normalized or not, but you can't
>normalize a view.

But you can drop a view that is in a low normal form and to create new views in 5NF.

>> >attributes
>> >[apply FDs to get to the next level, revealing PKs in the process]:
>> >relations (entities and relationships - an ERD is often created here)
>> >[apply transformation rules* to the ERD to get to the next level]
>> >-----boundry between logical and physical----------
>>
>> An ERD is a conceptual design, and if you apply "transformation rules"
>> to the ERD what you get is an incomplete logical design.
>
>Not in the least bit correct. Assuming the ERD itself is correct (a fair
>assumption), and you follow the rules, you ALWAYS end up with a database
>that is in at least 3NF.

But it does not have relationship with what I said.

I meant that the ERD is at the conceptual level and the SQL database design is at the logical level.

Regards Received on Fri Feb 04 2005 - 16:15:23 CET