Re: Conceptual, Logical, and Physical views of data

mAsterdam wrote:
> dawn wrote:
> > 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.
>
> When the implementation discussions slow down,
> the differences at the conceptual level become clear.
> Q: What's the difference between a terrorist and a methodologist?
> A: You can reason with a terrorist.
> (C) Martin Fowler

I've used that with a slight variation, replacing the word "methodologist" with "teenager".

> >>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.
>
> You are the mathematician. I'm not.

You should know better than to call me that, mAsterdam! Once upon a time I might have gotten an MS in Mathematics, but I opted for a ph.d. for the hubby first and then kids changed my priorities. Over time I've lost pointers (or key values?) to most such data and I'm nowhere close to being a mathematician. I'm just an application software developer with a few other hobbies ;-)

> I'm just an experienced DB guy.
> (With a good methodologigal (J.J. Klant) education, though. Main (not
> full) disclosure: economics with a math accent).

OK, so we are at least even up then -- a little theory somewhere in the grey matter, a somewhat logical inclination, and a practitioner's sensitivities.

> >>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
>
> It is not. Just think of how to handle the decision
> of choosing a primary key between the alternatives
> (another thread). Not necessary in say a CODASYL context.

Oh, you need not convince me - I'm definitely with you on this one. cheers! --dawn

> >>>The physical model is dependent on all of the above.
Received on Fri Sep 02 2005 - 01:58:04 CEST