Re: Conceptual, Logical, and Physical views of data
Date: Thu, 01 Sep 2005 20:49:06 +0200
Message-ID: <43174ca3$0$11071$e4fe514c_at_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 - 20:49:06 CEST