- From: Ian B. Jacobs <ij@w3.org>
- Date: 17 Jun 2003 08:42:33 -0400
- To: Dominique Hazaël-Massieux <dom@w3.org>
- Cc: ijacobs@w3.org, www-qa-wg@w3.org
On Tue, 2003-06-17 at 08:24, Dominique Hazaël-Massieux wrote: > Hello Ian, > > As we were discussing some of the issues you raised during our Last Call > period of the Specifications Guidelines, we were wondering if you could > explain us in which circumstances and for what reason you think it can > be better not to use RFC 2119 keywords to indicate conformance > requirements in a specification. > > For instance, in UAAG10, you apparently chose to use imperative verbs as > an equivalent to MUST; as we're trying to clarify our checkpoints on > conformance requirements, getting a better understanding on this would > be really helpful for us. Hi Dom, The UAWG realized it needed more conformation granularity than that offered by RFC2119 alone. At face value, RFC2119 enables one conformance level: all of the MUST requirements. The HTTP/1.1 spec uses RFC2119 to achieve two conformance levels: "An implementation that satisfies all the MUST or REQUIRED level and all the SHOULD level requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the MUST level requirements but not all the SHOULD level requirements for its protocols is said to be "conditionally compliant."" UAAG 1.0 has three conformance levels, and uses profiles. Thus, RFC2119 alone didn't work for us. We had to say "When we say MUST, we mean RFC2119 MUST, but only within the scope of the current conformance level or profile." Furthermore, UAAG 1.0 (like the other WAI Guidelines) uses the imperative voice to express the requirements, so the "MUST" is usually implied. One reason we did this was to avoid repeating at the beginning of each checkpoint "The user agent MUST ..." For A/AA/AAA, we might have been able to stick with MUST/SHOULD/MAY, except that by having AAA be defined as "The user agent satisfies all of the MUST/SHOULD/MAY requirements," we felt we would be in contradictionw with RFC2119, which says for the definition of MAY: "This word, or the adjective "OPTIONAL", mean that an item is truly optional." We did not feel that that definition aligned with "AAA" enough, since AAA meant that the MAY items were no longer optional. - Ian -- Ian Jacobs (ij@w3.org) http://www.w3.org/People/Jacobs Tel: +1 718 260-9447
Received on Tuesday, 17 June 2003 08:42:47 UTC