Re: domains aren't subtypes, right?

andrewst wrote:

> Type CITY is neither a supertype nor a subtype of STRING, it is a type
> that is represented using a STRING.

I though something similar, though I put it different: The confusion here arises from the unfortunaty naming of the type. Do you mean CITY or CITY_NAME? That are different concepts which get mixed up here. I could be convinced to see a CITY_NAME as a subtype (restriction) of STRING, and it would make sense to have string operations like concat on it.

The two types CITY and CITY_NAME would also have different domains ({the actual place Paris, London, ...}) vs. {the string "Paris", "London", ...}.

I am not quite sure about the equivalence of types and domains though. I actually had a related posting here recently (domain theory and databases) in which I asked for literature regarding this issue. Are databses just abusing the mathematical term "domain" when they really want to say type, or is it all equivalent?

Mathias Received on Fri May 23 2003 - 16:28:44 CEST