Re: OOD, Ada, and Inheritance

[mole-end!mat@uunet.uu.net]

In article <1992Nov5.190921.21374@sei.cmu.edu>, wellerd@ajpo.sei.cmu.edu (David
 Weller) writes:
> In article <mmaccorm.47@fox.nstn.ns.ca> mmaccorm@fox.nstn.ns.ca (Mike Mac Cor
mack) writes:
> >If Ada software is being designed using OOA and OOD, should inheritance be 
> >avoided (or prohibited) in the design process, as Ada does not provide 
> >inheritance? 
 
> ...  the Space Station Verification and Training Facility, is
> applying both OOA and OOD.  It is definitely a non-trivial project, ...
 
> Our inheritance is "manual", ... pass-through calls and composition
> to simulate "real" inheritance.  ...  we intend to quickly
> transition to Ada 9X, ...  In the 30 year life of this project, we
> we felt that [this] would give bigger payoffs than [ignoring inheritance].
 
> It seems silly to sacrifice a design to fit in a current language.
> Especially when you know that language will support those
> "prohibited" features in about 2 years.

I'd think that you'd want to distinguish between inheritance that models
the problem, inheritance that models the solution, and inheritance as
an implementation tool.

Inheritance that models the problem is probably worth staying with, even
at a high present cost and a high risk of subtle differences between your
`simulation' and the actual feature.

Inheritance that models the solution is probably economical only if it
has a very high present value and if it will be flexible enough to be
reimplemented cheaply with whatever version of inheritance is added to
the language.

Inheritance as an implementation tool is probably not worthwhile unless
it confers a very strong and very specific architectural advantage.

(Just my $0.02 worth ...)
-- 
 (This man's opinions are his own.)
 From mole-end				Mark Terribile

 mat@mole-end.matawan.nj.us, Somewhere in Matawan, NJ