RE: [DR 702] Why compare two messages?

> > The sentence starting "This mechanism... must ensure that given two XP
> > messages..." seems to suggest that evolution is implemented
> > as a relation
> > on two or more messages.  I don't think this is necessarily
> > so.  There are
> > all sorts of ways to evolve protocols without there being a 1-for-1
> > equivalence of messages.  Furthermore, the sense in which two messages
> > might be "compatible" is not even defined informally.  Also, the
> > requirement is a bit vague on the degree to which the intention is to
> > ensure evolvability of XP itself, vs. protocols built using XP.
>
> I think the last sentence might be the problem. I think the point of the
> text above was to focus on evolvability of XP itself and not protocols
> built using XP (and I agree with your concern if that is the case). One
> way we might be able to clarify this is to change "given two XP messages"
> to "given two XP envelopes". Comments?

I believe that Noah has the right of this on the first point that using the
example of n messages is somewhat misleading. What we need to do, as an XP
processor, is to be able to take _one_ message and decide whether or not
that message is compatible to our processing ability. So I propose we
replace
the sentence in 702 which states

"This mechanism or mechanisms must ensure that given two XP messages it
should be possible, by simple inspection of the messages, to determine if
they are compatible."

and replace it with

"This mechanism or mechanisms must ensure that an XP processor, by simple
inspection
of an XP envelope, may determine whether or not the envelope is compatible
with
its processing ability"

The intention of the requirement is to provide some support both for the
evolution of XP _and_ for support of applications/protocols that will use
XP.
Both of these were identified as sub-requirements for extension and
evolution
in general and so they were glommed together. I would have no objection to
splitting this into two requirements if the fact that we are looking for
both
is confusing.

 cheers
   --oh

--
ohurley at iona dot com
+353 1 637 2639

Received on Tuesday, 14 November 2000 11:38:15 UTC