George,
We currently use MUST in regular cases and SHALL when we either want not
to create confusion where non-normative "must" is used or for aesthetic
reasons, eg. to make a requirement look not so strict as MUST implies
(even though formally they both have similar force). I personally use
SHALL when I mean "it is to be so" and not strict "it is mandatory and
obligatory and compulsory and <...> to be so".
CAN and CANNOT are an interesting idea, but they have little in common
with conformance. Current 2119 language, as primarily used in
<http://tools.ietf.org/html/rfc1123#page-11>, was intended to clear up
the requirements on support of particular feature(s). Yes, it is
sometimes desired to express possibility and allowance, but IMO simple
"can" and "cannot" are fine for this purpose.
I don't actually think Annex H of <I don't know what since you're
providing only part of it> should be referenced in 2119bis.
Mykyta Yevstifeyev
01.09.2011 16:17, George Willingmyre wrote:
I offer for consideration in the attachment the ISO and IEC
requirements for use of the
terms "Shall" ; Shall not"; "Should"; "Should not" ; "May"; "Need
not" ;
"Can'; "Cannot" in ISO and IEC standards.
This document explains why ISO/IEC selects "Shall" and "Shall not" rather
than "Must" and "Must not" to denote mandatory requirements.
"Do not use "must" as an alternative for "shall". (This will avoid any
confusion between the requirements of a document and external statutory
obligations.)"
It is in the interests of IETF to contemplate and perhaps reference this
ISO/IEC document somehow in our definition of the terms below
2.1. MUST . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. MUST NOT . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.3. SHOULD . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.4. SHOULD NOT . . . . . . . . . . . . . . . . . . . . . . . . 4
2.5. MAY . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
George T. Willingmyre, P.E.
President, GTW Associates
Spencerville, MD USA 20868
301.421.4138
www.gtwassociates.com
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