Re: Objects and Relations

"JOG" <jog_at_cs.nott.ac.uk> wrote in message news:1171892555.782718.193500_at_q2g2000cwa.googlegroups.com...

[big snip]

> No comment on this? I've offered to points indicating to how thinking
> in terms of entities can be unproductive - the lack of success of E/R
> modelling in replacing RM (which was its original goal), and the
> collapse of the entity-based manipulation of Classical AI in the 70's.
> There is insight in both of these.
>

I challenge whether replacing RM was, in fact, the original goal of Peter Chen. It seems to me from reading his papers, as though he wanted to provide an alternative to RM in situations where RM was not particularly relevant to the implementation environment. An example might be implementation in a Codasyl database. RM would give you a handle on the design of the Codasyl database, but it wouldn't be a particularly useful handle. ERM would give you an equally useful handle on the design of a Codasyl database, but with far less effort, and with far less implicit design in the modeling effort.

I myself have actually benefitted from this situation. In a database design situation, my colleague had taken the trouble to create an ER model out of a Codasyl DB design for a fairly large part of a fairly complex enterprise. The requirement to design a relational (OK, OK, SQL) database for reporting purposes required almost no preliminary conceptual database modeling, because the ER model was still relevant to the enterprise's data.

The fact that producing an RM out of an ERM is easy and straightforward is no accident. Received on Mon Feb 19 2007 - 20:32:28 CET