[rfc-i] Excursion on RFC 5444 [Was:Re: Jave ascii art editor]

Dearlove, Christopher (UK) chris.dearlove at baesystems.com
Wed Jun 25 04:29:12 PDT 2014


We really weren't into complexity in our usage. + * and ? was about all that was needed. And () for grouping (rather than matching). The latter could have been avoided by intermediate definitions.

I suspect we might have caught some flak from some regexp experts on the () front. But that wasn't the sort we had.

(I believe in ABNF we could then have encoded that the bottom of the hierarchy elements were e.g. 8 bit numbers, instead of doing that in text. But we needed text anyway to indicate other constraints, e.g. that index_start <= index_stop.)

I also would never get rid of the graphics - in fact the main discussion there was did we need to present all the options. But they are non-normative (and, annoyingly and primarily my fault, with at least one erratum).

(For anyone who looks at 5444, all the pictures in it were drawn with a tool I put together.)

-- 
Christopher Dearlove
Senior Principal Engineer, Communications Group
Communications, Networks and Image Analysis Capability
BAE Systems Advanced Technology Centre
West Hanningfield Road, Great Baddow, Chelmsford, CM2 8HN, UK
Tel: +44 1245 242194 |  Fax: +44 1245 242124
chris.dearlove at baesystems.com | http://www.baesystems.com

BAE Systems (Operations) Limited
Registered Office: Warwick House, PO Box 87, Farnborough Aerospace Centre, Farnborough, Hants, GU14 6YU, UK
Registered in England & Wales No: 1996687


-----Original Message-----
From: rfc-interest [mailto:rfc-interest-bounces at rfc-editor.org] On Behalf Of Riccardo Bernardini
Sent: 25 June 2014 10:37
To: rfc-interest at rfc-editor.org
Subject: Re: [rfc-i] Excursion on RFC 5444 [Was:Re: Jave ascii art editor]

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On Wed, Jun 25, 2014 at 11:14 AM, Dearlove, Christopher (UK) <chris.dearlove at baesystems.com> wrote:
> One could have a valid discussion on which formalisation to use. ABNF may be official, but really not many people are familiar with it. Regexp is familiar to I believe many more people, but its normal purpose is not as a specification.
>

It should be said, however, that ABNF is more powerful of Regexp (at least in its original form that describes regular languages; I agree that there are some extensions that increase the power of Regexp).
Moreover, I find most ABNFs quite more readable than a Regexp of mild complexity.

> But a formalisation of format is good. I recently tripped up (temporarily) misinterpreting a picture-based definition in an older RFC (less than half of current numbering) - I misinterpreted which unit was to be repeated when given an ellipsis block. A formal specification would have helped.

+1 from me about the need of a formal description.  Actually, in some
cases I use both: the graphical representation is more intuitive and easier to understand by a human being, the formal description is (should be) more unambiguous and precise.  Just make clear that the picture is only informative, while the ABNF (or other formal
description) is normative.  In case of mismatch the normative description wins.

>
> (The biggest block - not Elwyn - to 5444 was at least one person who 
> didn't believe that a format should be specified independently of a 
> protocol. Another issue.)
>
> --
> Christopher Dearlove
> Senior Principal Engineer, Communications Group Communications, 
> Networks and Image Analysis Capability BAE Systems Advanced Technology 
> Centre West Hanningfield Road, Great Baddow, Chelmsford, CM2 8HN, UK
> Tel: +44 1245 242194 |  Fax: +44 1245 242124 
> chris.dearlove at baesystems.com | http://www.baesystems.com
>
> BAE Systems (Operations) Limited
> Registered Office: Warwick House, PO Box 87, Farnborough Aerospace 
> Centre, Farnborough, Hants, GU14 6YU, UK Registered in England & Wales 
> No: 1996687
>
>
> -----Original Message-----
> From: rfc-interest [mailto:rfc-interest-bounces at rfc-editor.org] On 
> Behalf Of Elwyn Davies
> Sent: 24 June 2014 23:44
> To: Thomas Clausen
> Cc: rfc-interest at rfc-editor.org
> Subject: [rfc-i] Excursion on RFC 5444 [Was:Re: Jave ascii art editor]
>
> ----------------------! WARNING ! ---------------------- This message originates from outside our organisation, either from an external partner or from the internet.
> Consider carefully whether you should click on any links, open any attachments or reply.
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> --------------------------------------------------------
>
> [Totally off topic]
>> For the format defined in RFC5444 (a regexp derivative - and here’s a 
>> memory test, Elwyn, who was the GEN-ART reviewer for that document?)
>
> Had to retrieve that one from tertiary storage! :-)
>
> January 2008 was a while and about 80 gen-art reviews ago! ARRGH!!!
> Quite a contentious one that.  RegExp raised a few hackles (I was quite mild on that one I thought).
>
>
>>  and used in a few protocols now,
>
> Perhaps we should try out RFC 5444 for the DTN BPbis (coming to an incipient DTN WG maybe after Toronto).
>
> I have to say that there are aspects of the existing RFC 5050 BP that might be better expressed as ABNF (or a RegExp grammar).
>
> /elwyn
>
>
>
>
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