From: Charles Lindsey (chl@clw.cs.man.ac.uk)
Date: Mon Oct 14 2002 - 06:56:20 CDT
In <bf04751f07dc9446.dlg@meowing.net> "greg andruk" <gja@meowing.net> writes:
>In local.usefor you wrote:
>> In <3DA506DB.6060206@meowing.net> greg andruk <gja@meowing.net> writes:
>>
>>>Charles Lindsey wrote:
>>>> Yes, when you introduce a brand new feature into a protocol, you do not
>>>> expect it to interoperate with the existing base.
>>>If it's been done right, a new feature does interoperate, providing
>>>graceful degradation. That involves reducing functionality for the
>>>older components rather than outright breaking it.
>> Read what I wrote.
>Write what you mean.
I did.
>> You do not expect the "new feature" to interoperate
>> with the existing base (though naturally it should also ause no harm). You
>> DO expect the "old features" to continue operating as before.
>In networking, when we say that things interoperate, we mean that they can
>successfully communicate with one another. That's the entire *point* of
>using a layered namespace, to ensure that each and every article can be
>successfully transmitted intact across old and new software alike.
Exactly. So if you use a feature that is 'new' in the revised protocol you
don't necessarily expect it to communicate with old software (though you
should aim for a gracewell degradation such that all parts of the message
not involving the new feature arrive and can be read). You DO expect
messages that do no use the new feature to continue to work.
Now in the matter in hand (UTF-8) we actually do better than that. We have
established that the new feature causes no _global_ problems. I.e. the
new stuff is propagated around the world and is available to any server
that cares to receive it.
The problems that remain are _local_ ones. If you want to read the new
stuff comfortably, you need an upgraded user agent. If you want to post to
moderated new-style groups, your local injector needs to be upgraded. If
you want to gateway the new stuff to email, your gateway may need to be
upgraded.
But in most of these cases (not the moderation) the degradation is likely
to be graceful, insofar as the message you see, or the email that is sent,
may be munged, but the bits that were in ASCII will still be intact.
-- Charles H. Lindsey ---------At Home, doing my own thing------------------------ Tel: +44 161 436 6131 Fax: +44 161 436 6133 Web: http://www.cs.man.ac.uk/~chl Email: chl@clw.cs.man.ac.uk Snail: 5 Clerewood Ave, CHEADLE, SK8 3JU, U.K. PGP: 2C15F1A9 Fingerprint: 73 6D C2 51 93 A0 01 E7 65 E8 64 7E 14 A4 AB A5