Re: domain questionnaire

On 21 Feb 2001 10:58:14 GMT, hidders_at_REMOVE.THIS.win.tue.nl (Jan Hidders) wrote:
>I think this touches a deep philosophical problem with the relational
>model.

Yep. It's something I had intuitive questions about from day one, but only understood the formulation of in the last couple of years.

>The other approach is that you use a
>fancier data model such as the Ent.-Rel. Model, UML class diagrams, ORM
>or whatever, and then "implement" this in the form of relations. In
>this case the relational model is used as an "implementation model" (if
>that is the proper word) and then the arguments by Codd and Date do not
>seem to apply directly.
>
>Or do they? :-)

Well, Codd has mostly been quite, but Date has mostly been noisy, over the past ten years or so, ranting about how objects were evil, to make a long story short. And, frankly, he had many valid points. IMHO. In the last year or two, Date has been trying to make peace with objects, and trying to ignore or disown his own earlier statements. No, I don't have any specific pointers or citations handy. The one point that I think the object people got right (by accident, perhaps) all along, and that Date could not accept because it violates the basic dogma of relational theory, is that an object (read: attribute or tuple) might have an identity separate from its value. But I do not think that either side, object or relational, has yet described a theoretically-based way to merge object identity and relational algebra.

Which is to say, that the issue of whether a database should reflect an external ontology or not (and if so, how, and by what theory), I think maps directly to this issue of how object identity must be handled, ... although I admit that the derivation and proof of this assertion by me would be interesting to see formally presented, as I do NOT attempt to do here ... but may do elsewhere, at some point.

Joshua Stern
JRStern_at_gte.net Received on Wed Feb 21 2001 - 21:31:57 CET