Re: Difference between inheritance and package use

[chuck@brain.UUCP (Chuck Shotton)]

In article <1991Jun22.013149.28268@netcom.COM>, jls@netcom.COM (Jim Showalter) writes:
> For example, I look around in nature and, yes, I do find examples of
> inheritance. But I also find tractors. And there are, to the best
> of my ability to discern their presence, scant few examples of
> inheritance in tractors. What I find in tractors is subassemblies
> (big ones, such as chassis, electrical, etc--subsystems), which
> in turn are decomposed into smaller components such as differentials,
> which are in turn decomposed into yet smaller components such as
> wrist pins and gaskets and knobs. And so forth, all the way down
> to quarks. And what is true for tractors is true for the human
> body, airplanes, telephones, and just about every other physical
> object I come into contact with--it is built up from smaller pieces.
> 

I think you've actually defined when each "branch" of the tree is utilized
without realizing it. Sure, there are tractors. And they are forms of 4 wheeled,
utilitarian locomotion, which are a sub-class of wheeled transportation and
a peer class to 4 wheeled recreational vehicles. Wheeled transportation is
a form of land vehicle, which is a subclass of vehicles in general.

Looking at the problem this way, it seems that inheritance, etc. is better
suited to decomposing the higher levels of abstraction, while packages, etc.
are better suited (as mentioned in your example above) to implementation details.
Which, amazingly enough, is one of the major features of the package construct
(hiding implementation details). I don't think you'll see a totally object
oriented LARGE system for a long time. Some hybrid of OOP and traditional
decomp., maybe. 

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Chuck Shotton                 Internet:  cshotton@girch1.med.uth.tmc.edu
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