Pachyderm in the parlor (Was: 2119bis)

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On 8/31/11 12:36 AM, Eric Burger wrote:
My interpretation of what you wrote is that in your mind there is absolutely no difference between a SHOULD and a MAY.  They are both optional, and you implement whatever you have time to implement, with SHOULD's prioritized higher than MAY's.

Even if that is not what you mean, it is what many implementors do.

Peter's document makes a change to 2119 that nobody has mentioned yet, and I think it is the one that is causing most of the strife in this discussion.

Hector is exactly right. SHOULDs are optional. MAYs are optional. What he fails to point out is that MUSTs are also optional. They're all optional because.....

RFC 2119 does *not* provide *conformance* terms.

Peter's document uses the words "conform" and "conformance". They appear nowhere in RFC 2119. RFC 2119 was not coming up with a vocabulary for things that MUST be done if one is to conform to a specification. It came up with terms for things that MUST be done to interoperate. Or SHOULD be done (with a pretty specific meaning of "SHOULD"). Or MAY be done.

If you think that the presence of SHOULD means that you don't have to implement a particular thing in a document, you're wrong. SHOULD means that "may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course." That is, if you don't do what is in the statement marked by "SHOULD", there is a good chance you will fail to do something that is "required for interoperation" or to engage in "behavior which has potential for causing harm" unless you understand the implications.

But if you think that the presence of SHOULD (or MUST) means that you *have to* implement a particular thing in a document, you're also wrong. There are not protocol police. We don't do conformance checks in the IETF.

You might have a contract with someone who requires you to implement all MUSTs (or SHOULDs unless you provide an explanation of why you didn't). That's up to them. But the IETF ought not be in the business of conformance requirements.

Maybe we do write documents now with conformance requirements. Maybe this ship has sailed. Maybe the elephant is on board. I hope not.

Clarifying "SHOULD" is a fine thing. Making it conformance language is not. I don't like the 2119bis document in its current form.

pr

--
Pete Resnick<http://www.qualcomm.com/~presnick/>
Qualcomm Incorporated - Direct phone: (858)651-4478, Fax: (858)651-1102

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