Re: Conceptual, Logical, and Physical views of data


"Dan" <dan@xxxxxxxxxx> wrote in message
news:dH2Re.2162$yn2.5505@xxxxxxxxxxxxxxxxxx

> I thought the 3 layers were:
>
> 1 - The conceptual which deals with end users and client programing.
>
> 2 - The logical that deals with the design on the database and
> maintaining the data.
>
> 3 - Th physical which is how the DBMS stores the data on disk and in
memory.
>

Hmmm... That's different from the way I learned it. I'm not saying "mine is
better". But I am saying that I'm more comfortable with mine.

First off, I draw a distinction between the "end user" and the SME. The
SME has to understand the subject matter, in quite some detail, although not
the level of detail needed for database design. The end user is sometimes
like the end user of an ATM. This user only remembers the tiny amount
needed to do his transactions, and drive or walk away. So when I say the
conceptual is the SME view of the data, I'm really not talking, necessarily
about end users at all.

Of course, some people might be both SMEs and end users, or SMEs and
database designers, or even SMEs and programmers! (ducking). But the
roles are still distinct.

Your level 3 and my Physical view seem about the same to me.

I'm not sure what your level 2 is. For example, if I'm designing an Orace
database, and I decide how big to make a TABLESPACE and what the fill factor
is going to be, is that part of 2 or part of 3?




.