Re: SHOULD vs MUST
John C Klensin <john-ietf@jck.com> Wed, 25 June 2008 17:37 UTC
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Date: Wed, 25 Jun 2008 13:37:38 -0400
From: John C Klensin <john-ietf@jck.com>
To: Scott Brim <swb@employees.org>
Subject: Re: SHOULD vs MUST
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--On Wednesday, 25 June, 2008 13:02 -0400 Scott Brim <swb@employees.org> wrote: > On 6/25/08 8:24 AM, John C Klensin allegedly wrote: >> >> --On Wednesday, 25 June, 2008 07:59 -0400 Scott Brim >> <swb@employees.org> wrote: >>> ... and draft authors should include explanations in their >>> drafts of the reasons an implementor might legitimately have >>> for not implementing the "should". For example, an older >>> operating system that does not support a new capability. > > >> Do you really mean, e.g., >> >> ... where feasible and, in the author's judgment, >> appropriate, it is desirable to include explanations or >> illustrations of the exception cases in drafts that use >> SHOULD. >> >> ??? >> >> I've run into a number of situations over the years in which >> there are known edge cases that prevent a MUST but where those >> edge cases are rare and obscure enough that describing them >> would require extensive text. > > My rule of thumb is: when you're writing the draft if > something is not a MUST, ask yourself "why not?" and write > down your answer. You can be brief but make it clear that the > SHOULD is a MUST with exceptions. > > There's no way we should have strict process rules about this. > The IETF has enough rules as it is. However, explanations of > SHOULDs do make better standards. The point is to give > guidance to implementors. I did an informal survey last year > and found that some implementors treat every SHOULD as a MUST, > but more of them just treat a SHOULD as a MAY, essentially to > be ignored. An explanation of the circumstances surrounding a > SHOULD will lead to a lot more consistency in implementation. > Many SHOULDs in RFCs are because there are old implementations > that need to be taken into account, or because some capability > isn't widely possible yet but will be within the lifetime of > the standard. If a MUST becomes a SHOULD to take that into > account, and you explain it, your chances of getting rid of > non-MUST-capable implementations eventually goes up > tremendously. So, to reiterate, when you're writing the draft > if something is not a MUST, ask yourself "why not?" and write > down your answer. Certainly we are in complete agreement about the principles here. We probably also agree about Fred's slightly different take, which is thinking about whether a proposed MUST really might have exception cases that we would prefer to keep within the bounds of the standard. My concern is about anything that might get turned into another rule while various of us are trying to concentrate on technical work and not, e.g., watching every entry in the IESG's tracker logs. More generally, thinking carefully about these conformance statements is A Good Thing and should be encouraged whenever possible. john > > _______________________________________________ IETF mailing list IETF@ietf.org https://www.ietf.org/mailman/listinfo/ietf
- Review of draft-ietf-geopriv-http-location-delive… Eric Rescorla
- Re: Review of draft-ietf-geopriv-http-location-de… Hannes Tschofenig
- Re: Review of draft-ietf-geopriv-http-location-de… Eric Rescorla
- Re: Review of draft-ietf-geopriv-http-location-de… Hannes Tschofenig
- Re: Review of draft-ietf-geopriv-http-location-de… Eric Rescorla
- Re: Review of draft-ietf-geopriv-http-location-de… Eric Rescorla
- Re: [secdir] Review of draft-ietf-geopriv-http-lo… Richard Barnes
- RE: [Geopriv] [secdir] Review ofdraft-ietf-geopri… Tschofenig, Hannes (NSN - FI/Espoo)
- Re: [Geopriv] Review of draft-ietf-geopriv-http-l… Eric Rescorla
- RE: [Geopriv] Review of draft-ietf-geopriv-http-l… Tschofenig, Hannes (NSN - FI/Espoo)
- RE: Review of draft-ietf-geopriv-http-location-de… Mary Barnes
- Re: Review of draft-ietf-geopriv-http-location-de… Eric Rescorla
- Re: Review of draft-ietf-geopriv-http-location-de… TSG
- SHOULD vs MUST (was Re: Review of draft-ietf-geop… Lawrence Conroy
- Re: SHOULD vs MUST (was Re: Review of draft-ietf-… Eric Rescorla
- RE: [Geopriv] Review of draft-ietf-geopriv-http-l… Dawson, Martin
- Re: SHOULD vs MUST (was Re: Review of draft-ietf-… Dave Cridland
- Re: SHOULD vs MUST (was Re: Review of draft-ietf-… Joe Abley
- Re: SHOULD vs MUST Frank Ellermann
- Re: SHOULD vs MUST (was Re: Review of draft-ietf-… Iljitsch van Beijnum
- Re: SHOULD vs MUST Fred Baker
- Re: SHOULD vs MUST Scott Brim
- Re: SHOULD vs MUST John C Klensin
- Re: SHOULD vs MUST Fred Baker
- Re: SHOULD vs MUST Scott Brim
- Re: SHOULD vs MUST John C Klensin
- Re: SHOULD vs MUST Scott Brim
- Re: SHOULD vs MUST Dean Willis
- Re: SHOULD vs MUST Robert Sparks
- Re: SHOULD vs MUST Dave Crocker
- Re: SHOULD vs MUST Dave Cridland
- Re: SHOULD vs MUST Iljitsch van Beijnum
- SHOULD vs MUST case sensitivity Dave Crocker
- RE: SHOULD vs MUST case sensitivity Eric Gray
- Re: SHOULD vs MUST case sensitivity Julian Reschke
- Re: SHOULD vs MUST case sensitivity Keith Moore
- SHOULD vs MUST case sensitivity Dave Crocker
- RE: SHOULD vs MUST Eric Gray
- SHOULD vs MUST case sensitivity Dave Crocker
- Re: SHOULD vs MUST case sensitivity C. M. Heard
- Re: SHOULD vs MUST case sensitivity Iljitsch van Beijnum
- Re: SHOULD vs MUST case sensitivity Randy Presuhn
- Re: SHOULD vs MUST case sensitivity Dave Crocker
- Re: SHOULD vs MUST case sensitivity Dave Crocker
- Re: SHOULD vs MUST case sensitivity Randy Presuhn
- Re: SHOULD vs MUST case sensitivity Keith Moore
- Re: SHOULD vs MUST case sensitivity Dave Crocker
- RE: SHOULD vs MUST case sensitivity Eric Gray
- Re: SHOULD vs MUST case sensitivity Spencer Dawkins
- Re: SHOULD vs MUST case sensitivity Ralph Droms
- Re: SHOULD vs MUST case sensitivity Dave Crocker
- RE: SHOULD vs MUST case sensitivity Hallam-Baker, Phillip
- Re: SHOULD vs MUST case sensitivity John Levine
- RE: SHOULD vs MUST case sensitivity Hallam-Baker, Phillip
- Re: SHOULD vs MUST case sensitivity John Leslie
- RE: Review of draft-ietf-geopriv-http-location-de… Mary Barnes