From: Sebastian Hanigk <hanigk@...>
Date: 2007-03-30T18:05:04+09:00
Subject: Re: Object/Relational Mapping is the Vietnam of Computer Sci

Jochen Theodorou <blackdrag@uni.de> writes:

>> The inheritance relation of an ER model can be represented in the
>> table model as views. Depending on the circumstances, it might be
>> favourable to model the subclasses as distinct tables and the
>> respective superclasses as views or the other way around.
>>
>> Either way, queries over the subclasses will query the superclasses, but
>> that's not different from the OO point of view.
>
> combining it with a view is surely a good idea. It makes the queries
> more easy. I don't want to say it is different, it is just not as nice
> as with normal tables.

The point is not that a view simplifies a query over a given inheritance
relation, a view is the table model implementation of ER-inheritance.

In general - and I have sometimes learned it the hard way - you have to
be very careful about what model one is talking: usually the highest
level is the ER model which will be implemented as a relational model
that will be (or can be) normalised and at last this relational model
will be implemented as a table model.

>> As Austin already has mentioned, object modeling can be seen as a
>> special form of ER modeling - which explains the plethora of
>> dysfunctional and outright ugly object hierarchies one encounters in
>> software engineering because those people do not understand the
>> fundamental mathematics.
>
> I don't agree with austin and the resulting ugly class hierarchy is
> prove enough for me. Not in all cases of course ;)

Ah, I think I have been misunderstood: ugly object models are mostly
produced by 損software engineers束 who have no knowledge about the
fundamentals of ER modeling.

> Why not consider OODB mathematics as part of graph theory and others?

There is no such thing as OODB mathematics in a usable, formal sense.


Bye!

Sebastian