Re: Conceptual, Logical, and Physical views of data

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Wed, 31 Aug 2005 23:50:42 +0200
Message-ID: <4316259f$0$11064$e4fe514c@news.xs4all.nl>

David Cressey wrote:
> Dan wrote:
>

>>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.

The roles vary with your system development methodology and the nature of your project.
What impact does the activity database design have on the necessary roles? This is an interesting question in it's own right. Does it matter if the technical architecture is given or not (say: we will use DBMS xyz)?

> 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?

3. Physical, like indexes. Received on Wed Aug 31 2005 - 16:50:42 CDT