[unios] Re: Reflection

[David Jeske]

David, your email turned into a treasure trove of concise
explanations.

On Tue, Jan 05, 1999 at 08:46:03PM -0800, Tril wrote:
> Reflection is the means by which any component at all can be
> replaced, no matter what part of the system it is in.  Reflection
> allows you, like Brian Rice said, to reach in to the system and
> choose the part you are interested in, then everything else becomes
> implicit.  In other words to rearrange the entire topology for a
> moment to expose that component, and arrange it back again with the
> component embedded in the rest of the system.

> Hmm, after a bit of revision that paragraph could go on the page :)

I agree, I like that description. It creates a good 'picture'.

> There is a hierarchy of specification-implementation each implementation
> being 'lower-level' than its spec.  High- and low-level are relative.  The
> lowest level is the specification for the hardware and its implementation
> is the actual hardware.  The next higher level is any specification that
> uses the hardware.  Of course for a system to work everything must be
> dependent on the hardware by some path through this spec-impl hierarchy.
>
> At *any* level in the hierarchy, the specification is independent of its
> implementation. And you can exchange the implementation for a different
> one by providing a different mapping from the spec to the new impl.

I like the above descipriont as well.

> I don't know what this is called, maybe OO, maybe "a component
> model".  Anyone know a better term?

In my experience, trying to explain this idea as a form of OO hinders
more than it helps. There is too much baggage in people's heads about
objects and classes. Unfortunatly, I don't have a better term either.

-- 
David Jeske (N9LCA) + http://www.chat.net/~jeske/ + jeske@chat.net