Re: domain questionnaire

Let me preface this by saying: "Beware the vociferous ignorami"

A domain is a declared set of values and the operations available on those values.

The answer to all of your questions is: That depends.

>1. coordinate x of a point in cartesian coordinates vs.
>angle theta in polar representation of point

In a precisely modelled system, angle and distance are clearly two different domains. However, one can represent each of them as a real or floating point number.

It makes no sense to add an angle to a distance, and declaring separate domains for each (with appropriate operators) enforces this sensibility. However, if a designer decides that a system does not need such enforcement and such precise modelling, one could declare each as some generic floating point number type.

In the latter case, the database has no knowledge that each is drawn from a different domain. To the database both have the same domain (generic floating point number type).

Complex number, on the other hand, is a single domain even though one can represent it in cartesian and polar coordinates. The database should manipulate two complex numbers of the same value with equivalent results regardless of representation.

>2. weight in lbs vs. weight in kgs

Weight in lbs and *mass* in kgs are clearly different domains. However, mass in grams and mass in kgs could be the same domain with two different representations. Mass would have the same operators defined regardless of representation.

Ideally, representation is independent of domain (or data type) to achieve the goal of physical independence.

>3. US voice stationary phone numbers vs. fax numbers vs. cell numbers

I would assume that all three would have the same domain. In the end, the number only identifies a node in the telephone network. Two numbers identify the circuit in my home. One of the numbers reaches my cell phone first, when available. The circuit in my home has telephones, modems and a fax machine connected to it.

However, that does not prevent some country from creating a crazy standard with differing numbers of digits for each type of device. And it does not prevent telephone companies from reserving ranges of numbers based on intended primary use regardless of actual use. Received on Fri Feb 23 2001 - 02:03:59 CET