Re: [Sip] Proposal of Non-Sequential Group Notion in ABNF w/ a SIP case

Paul Kyzivat wrote:
> I agree with Keith about the inadvisability of rewriting the grammar.
> Save it for SIP/3.0.
>
> In any case, I think the issue isn't with ABNF per se, its with the
> way ABNF was used for SIP. ABNF isn't actually able to represent
> everything that was desired for sip, so some things were simply
> handled as exceptions in the text.
>
> Of course the "right" thing to do would have been to either give up on
> anything that couldn't legitimately be represented, or else switch to
> some other specification language that could express what was intended.
not clear.  IMHO, trying to specify every aspect of detail of a protocol
syntax using a formal specification language can be misleading and cause
more interop failures, than a looser specification written in ABNF plus
some exceptions in the text.   One reason for the additional failures
when using the precise formal specification is that you don't really
benefit from that specification unless you feed it to a program that
will automatically generate the recognizer.  And if you do automatically
generate a recognizer from the formal specification, you often find that
it doesn't report errors in the way that you'd like, doesn't perform as
well as you want, etc.

The trick is to design the protocol in such a way that a precise formal
syntax specification is not necessary.   This implies having a certain
degree of simplicity and regularity in the protocol.
>
> But there is a big tradeoff there. At least many people are capable of
> reading ABNF, and a reasonable number of those can accurately
> understand what it means. A somewhat smaller, but still significant,
> number can write it correctly. Its important that the people involved
> in the standardization process, and that implement the standard, be
> able to understand it. A more powerful specification language, that
> fewer people could understand, might not be such a great choice.
exactly.

Keith