Re: Conceptual, Logical, and Physical views of data

mAsterdam wrote:
> 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.

I would agree that is the idea, but it seems rare that it works out this way.

> But what does it mean?
>
> 1. 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).

so true

> 2. How do we make the conceptual model explicit?

This is probably a naive response, but where I used to choose an early prototyping tool, possibly paper & pencil, even in the analysis phase of a project, I now use web pages. I can mock these up even in place of showing any end-user an erd (or uml class diagram) with any level of detail in it. If you model the conceptual data with web pages with foreign keys turned into links and sample data values, you can get a lot of bang for the buck.

I haven't done that from an existing implementation, but I can imagine doing so and I would think it could be similarly useful. Then if you want it all on one (giant) page, use a web diagramming tool to show the pages and their links. One page is one (typically strong) entity. You can use various xhtml features to include the definitions of terms on mouseover (I haven't done that).

You might be looking for a more formal modeling approach, in which case others will know a lot more than I.

> Is there an effective formalism which can serve
> as a modelling language before the logical model?

I'm guessing that saying I can do what I need using xhtml makes me sound on the not-exactly-professional side, but so be it.

> 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.

That seems close to what happens, although plenty of people seem to think that the logical model is db independent. --dawn

> > The physical model is dependent on all of the above.
Received on Thu Sep 01 2005 - 23:49:18 CEST