Re: Another view on analysis and ER
Date: Thu, 6 Dec 2007 01:56:52 -0800 (PST)
On 6 dec, 02:47, JOG <j..._at_cs.nott.ac.uk> wrote:
> On Dec 6, 12:18 am, Jan Hidders <hidd..._at_gmail.com> wrote:
> > On 5 dec, 13:52, JOG <j..._at_cs.nott.ac.uk> wrote:
> > > On Dec 5, 10:49 am, Jan Hidders <hidd..._at_gmail.com> wrote:
> > > > On 5 dec, 02:10, JOG <j..._at_cs.nott.ac.uk> wrote:
> > > > > So why on earth would /anyone/ want to drop step 3? I'm at a loss as
> > > > > to why certain cdt'ers (who are clearly intelligent people) seem to be
> > > > > advocating this. An absolute loss I tell you.
> > > > I'm not sure that is what Ruud is saying. Anyone else?
> > > Is this not what you were proposing yourself Jan in another thread -
> > > that the logical layer should not be neutral, but rather based on
> > > entities and relationships (and hence taking a specific conceptual
> > > viewpoint)?
> Did I misunderstand, or is this not what you currently favour?
I thought my question made that clear, but to be completely explicit about this: I certainly agree that the logical layer should be as neutral as possible, but I don't accept the idea that formulating it as an ER schema makes it necessarily less neutral than formulating it in a relational schema.
> > Why would an ER schema be necessarily less neutral than a relational
> > schema?
> Either we are crossing terminology, or this has already been
> highlighted earlier in the thread with reference to marriages.
Quite possible. To save time I am a bit picky about what I read and don't read, even withint a thread I find interesting, so I may have missed something.
> forces one to pick a single conceptual viewpoint (marriage as
> relationship/marriage as entity, etc), whereas a propositional
> encoding is neutral on the topic.
I'm sorry but that is complete nonsense. The two possible ER diagrams you're talking about here are mapped to different relational schemas by the usual mapping. So in the relational setting you also have to make that choice.
- Jan Hidders