Re: Object Class and Data Type

> A class hierarchy is intended to relate entities based on common behavior;

Actually a class is simply a user's way of organizing things based on some general characteristic which usually implies those thing have common behavior, just as values of a domain will.

> however, a set of data types is intended to
> elaborate the differences between sets of values.

The same could be said of different classes and their instances.

> So, for example, it is common for a class hierarchy to have a single root;
> often called object or entity. But data types rarely if ever inherit
> from a single basic data type.

Data types do infact have a root. That root being "thing". Each data type is a thing. However it is neither customary nor practical to think this way within RDM. Other data models allow this. Also one need not inherit anything from a commonality, but can and typically does.

> Furthermore, class itself is typically defined as an object with certain
> behaviors. On the other hand, one never sees data type, a base type,
> defined as a data type!

The base "type" of "data type" (ie int, char, str) is thing. Int is a thing. char is a thing. str is a thing. It is difficult to see and implement this in RDM because it's lowest fundamental unit of abstraction (aka relation) doen't go low enough. Received on Wed Mar 31 2004 - 01:22:47 CEST