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RE: [OT] Difference between an extensible versus an evolvable
Title: Message
I
think that these definitions work well in terms of an interface. However,
if one looks at an implementation X of an interface B, the implementation
might be said to 'evolve' if it changes without any change to the interface
B. Such 'evolution' might be to improve performance in some respect, with
better algorithms surviving and poorer algorithms being killed
off.
Chris
Angus
In my opinion,
if we refer to interfaces (or languages/syntaxes) rather than, generically, to
"information systems", the distinction between evolution and extension becomes
clearer and more useful.
My
concept of "extensible" interface is that the interface supports certain
rigorously-defined extensions to it with the following
property:
------------------
Given:
- an implementation that exposes the base
(non-extended) interface B;
- an implementation that exposes an extended
interface E1;
- an implementation that exposes another
extended interface E2,
a
program written to use interface B is guaranteed to work (as expected) when
using any of these three implementations, "thinking" that it is using an
implementation of interface B.
------------------
The
same concept of extensibility would also apply to
languages/syntaxes.
On
the other hand, if an interface or a language "evolves", one cannot expect
that the condition above is satisfied (although it could
be).
In
other words, while I expect to be able to use an extended interface as if it
were the corresponding base interface, I don't expect to be able to use
an evolved interface as if it were the corresponding unevolved
interface. Same thing for a language/syntax.
I
think "evolvability" in this context means simply that an interface or a
language can be modified easily, inexpensively, and nicely, in order to
meet new requirements - without implying that a user can ignore that there has
been a modification.
If
we refer to a system, I would say that it is possible for a system to
*evolve* while some of its interfaces are simply *extended* (while others
evolve).
Alessandro Triglia
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![RE: [OT] Difference between an extensible versus an evolvable](/images/get_stylus.gif)
