Re: Inheritance

On Mon, 2002-08-19 at 15:42, Curt Sampson wrote:
> > A local constraint should be made obvious from looking at the schema,
>
> Ok, this now I could live with. Though I'm not sure that its
> theoretically very defensible, or worth the effort. Other languages
> that offer constraints, such as Eiffel (and soon Java), do not allow
> constraints that are not inherited, as far as I know. Do you have some
> counterexamples.

In Eiffel, at least, I can say "invariant feature_x" and redefine
feature_x in a descendant class, thus effectively redefining the
constraint. If we decide to inherit constraints unconditionally, the
application writer can achieve similar flexibility by moving the logic
of the constraint into a function whose behaviour depends on which table
it is used on. This would put the burden on the application rather than
requiring additional syntax in PostgreSQL.

--
Oliver Elphick Oliver(dot)Elphick(at)lfix(dot)co(dot)uk
Isle of Wight, UK
http://www.lfix.co.uk/oliver
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