Re: [port-srv-reg] we need to make progress

[Stuart Cheshire <[e-mail]>]

On 6 Sep 2010, at 16:02, Joe Touch wrote:

> ABNF may be hard for you to understand

I heard someone say once that an algorithm (or protocol) design can be so simple that it obviously has no errors, or so complicated that it has no obvious errors.

The issue I'm trying to raise is not the particular error I may (or may not) have found, but the deeper concern that I'm not confident that it does not have more errors in addition to that. The issue is that unless a reasonable proportion of the IETF community can look at the ABNF definition and state with confidence that it is obviously right, then we may publish something that's not right.

Processing a computer language generally consists of tokenizing followed by parsing. Tokenizing consists of turning text into logical units; parsing consists of turning those tokens into the language's structure. ABNF is a good way of expressing parsing rules; it is often not a good way of expressing tokenizing rules. The rules for stating what's a valid service name is a tokenizing problem, not a parsing problem. The awkward and convoluted ABNF in the document reflects this poor fit.

I suspect that most people reading this document skip over the ABNF bit, so it has not had good scrutiny. It's also not adding much to the document if it's text that most readers skip over.

Stuart Cheshire <[e-mail]>
* Wizard Without Portfolio, Apple Inc.
* www.stuartcheshire.org