Re: Conceptual, Logical, and Physical views of data

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Thu, 01 Sep 2005 20:49:06 +0200
Message-ID: <43174ca3$0$11071$e4fe514c@news.xs4all.nl>

David Cressey wrote:
> mAsterdam wrote:

[snip agreement]

>>Does it matter if the technical
>>architecture is given or not (say: we will use DBMS xyz)?

>
> Here's the way it works in practice for me:
>
> The conceptual model is implementation independent.

Agreed.

But what does it mean?

If there is no explicit conceptual model in an actual project different people will assume different models (not just homonym synonym stuff - ever tried modelling after a series of take-overs? Assumptions go deep).
How do we make the conceptual model explicit? Is there an effective formalism which can serve as a modelling language before the logical model? ORM? (Object Role Models - aside: some thought I was talking about Object Relation Mapping - a non-issue).

> The logical model is data model dependent (relational v. object oriented),
> but independent of product, volume, load, and resources.

> The physical model is dependent on all of the above.
>

>>3. Physical, like indexes.

>
> There's some disagreement about whether index design
> is part of the logical or physical design.
> I choose to include index design in the logical model, but very reluctantly.

Heh. Just checking :-) I'd say trust your reluctance.

OTOH, /some/ physical choices are feasibility issues, and should be cleared very early on, so there is no harm in delving deeply into /some/ indexes before there is a complete logical model. The same goes for conceptual/logical efforts, of course. Received on Thu Sep 01 2005 - 13:49:06 CDT