Re: One-To-One Relationships

On Dec 6, 8:12 pm, rp..._at_pcwin518.campus.tue.nl (rpost) wrote:
> JOG wrote:
> >[...] Ugh, that's even worse than a logical model based on ERM. Ah yes the
> >OO-data model, the very one that died on its ass because it was a
> >nightmare to query,
>
> Duh. Of course it isn't easy to query; that's what relational models
> are for. It's a compromise.

How is it a compromise? OO-DBMS give you nothing extra, and make querying harder. That's why the market for them failed.

> But it supports relational models.
>
> >nevermind the fact it was a retro-grade
> >reinvention of the network model that was superceded 30 years ago.
>
> The network model didn't have query at all, as far as I recall.
>
> >> > We can only ever
> >> >identify things from observable attributes (and refer to them by
> >> >attributes too!).
>
> >> Certainly, but we don't always make those attributes explicit.
>
> >Yes we do. Always.
>
> Not in my experience.

Then do you get sent messages from an omnipotent higher being to tell you the identity of something! ;) I simply cannot think of any example of how something is identified without using explicit, identifying attributes!

>
> >> And we don't always know what the relevant identifying attributes are.
>
> >Yes we do, otherwise we can't identify them in the real world.
>
> You mean, assuming that we can identify them consistently throughout
> the lifetime of the model. This is getting repetitive.

You don't need to assume that, its an absolute necessity. Otherwise you end up with a broken database. But I understand that your not seeing the practical issues of what I am saying, so maybe we should give up. I'm just trying to help you out - I get nothing myself out of these discussions!

>
> [...]
>
> >> Should I ever want to, let's say, meet you on IRC or over coffee, I'd need
> >> to extend my model of you, and provide a more detailed identification.
>
> >Nope, then you'd be dealing with a different entity.
>
> It depends on who you ask.

?

>
> [...]
>
> >> Please describe how you describe that persons are heads of departments
> >> in a way that doesn't predetermine how I'm going to identify persons
> >> and departments from now on. Or is it Just Wrong to want that? Why?
>
> >Well not just wrong, but nonsensical. How can you describe something
> >if you can't identify it? C'mon Reinier!
>
> I didn't say I can't identify it. I'm just saying I may not yet have
> determined how to identify it, or that I want to identify it differently
> tomorrow. This is getting repetitive.

If its identifying attributes are different tomorrow its a different thing! An identifying attribute cannot change, because it is used to distinguish an item from others, over its whole lifetime.

I think perhaps you have a different notion of what identification is.

>
> >> >> Does that mean
> >> >> we should express the meaning of that statement, the "head of department"
> >> >> relationship, as one between department names and person names?
>
> >> >Why not? Its just data. Whatever conceptual model we want to conjure
> >> >in our heads afterwards is our own business.
>
> >> Nope. We don't decide whether people change their names,
> >> the personnel administration does (where I work, at least).
> >> We don't want an administration with headless departments
> >> as a side effect of name changes.
>
> >I'm afraid you've missed the point. I've given you examples but I'm
> >not sure you have digested them properly mate.
>
> The feeling is mutual. This is getting repetitive.

I promise you I have been through these arguments before - In fact I'd say I didn't really understand the real advances that Codd made before I arrived at cdt, and got a free fast-track education. But gradually (and sometimes painfully) people a lot more knowledgeable than myself have helped clarify my thoughts, and now the logic seems to all fit.

OID's bad. Content based addressing good. Understanding that entities don't exist outside of their attributes, good (that was a painful one as I recall). Recognizing that identifying attributes cannot change, check. Understanding the impact that object containment has on querying and bias, also check. etc.

Perhaps you have not succinctly described what your actual point is due to the tit-for-tat responses that usenet debate engenders. Stating your whole point succinctly in 4 or 5 lines always helps.

> Thanks for the effort anyway; I still learnt some things.

Well I appreciate you saying that. Best of luck to you Reinier.

>
> [...]
>
> >I can only reccommend you go off and read all the arguments against
> >the disaster that has been OO-DBMS.
>
> Where?

Date, while I don't agree with some of the things he says, has written dozens of articles illustrating why db's based on OID's are deleterious. Pascal and Darwen have also published on the arguments against.

Even if I can't convince you of anything, most of the articles in "relational database writings" are a good read.

Regards, J.

>
> --
> Reinier
Received on Thu Dec 06 2007 - 22:27:02 CET