Re: Clean Object Class Design -- What is it?

>> I have some reservations about the relational model because relations do
 not
>> support the concept of a relationship;
>
>This is of course incorrect.

I had not seen this yet when I responded to your other message.

>However, is it necessary to have all three constructs (relations, tuples
 and
>domains) that the relational model provides? For example, the Lisp model
>provides two (atoms and lists) and the Smalltalk object model gets by with
>one (objects).

Relations are mathematical constructs. One can think of them as points in an N-dimensional space. One can think of them as sets of propositions. One can think of them simply as sets.

As a result, one can use first order predicate logic to improve the understanding of the data model, to query databases, to transform queries into useful logical equivalents etc. One can apply set theory to all of the same uses.

How is the Lisp model of atoms and lists equivalent to or derived from any branch of mathematics?

SmallTalk does not get by with one logical construct. It has object classes, object variables, references (ie. pointers) etc. While I do not know the details of the language, I am sure it also has at least one repeating group type such as array or collection. Does it have extents?

Stealing heavily from Chris Date (and Hugh Darwen) again: Think of domains (object classes) as the things we want to talk about and think of relations as what we want to say about them. I think it is reasonable to want to make statements regarding multiple things at once; hence, the tuple. I think it is reasonable to want to make the same statement about different combinations of things; hence, the relation. Received on Sun Jul 22 2001 - 04:54:25 CEST