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Re: [coremob/level-0] df3f70: Replace incorrect use of "MUST [...] if available"...

From: James Graham <jgraham@opera.com>
Date: Wed, 18 Apr 2012 14:59:08 +0200
Message-ID: <4F8EBA9C.4000907@opera.com>
To: Cuihtlauac ALVARADO <cuihtlauac.alvarado@orange.com>
CC: public-coremob@w3.org
On 04/17/2012 03:51 PM, Cuihtlauac ALVARADO wrote:
> Hi Tobie,
> Allow me to express my disagreement with respect to that change, and
> such kind of change in general.
> I share your interpretation of RFC 2119. "MUST" is an unconditionally
> requirement while "SHOULD" is a conditional requirement (i.e. "there may
> exists valid reasons [...] to ignore [...]"). Replacing "MUST if" by
> "SHOULD" is formally correct. However, in practice, "MUST if" is far
> superior to "SHOULD", the former should be preferred. Let me explain why.
> Basically, the "MUST if" clause comes with text which details the
> circumstances under which the requirement does apply, while "SHOULD"
> does not. In our case, we absolutely do not want a device which has a
> SMS app and the agent is *not* capable to trigger that SMS app using the
> sms: scheme. That must be avoided. We really want the URI scheme to be
> dispatched always, unless sending SMS is not possible. This was captured
> by "MUST ... (if available)", it is no longer by "SHOULD".
>  From test implementation perspective, the "MUST if" is easily turned
> into a real conditional statement, in contrast, it is impossible to
> decide, at test execution time, whether failing to comply with a
> "SHOULD" is actually valid or not.

I don't think there is a testable requirement here anyway. For example I 
might configure my device/ua to do nothing when an sms:// link is 
activated. Or a UA might have built-in support for the sms protocol that 
isn't via the system SMS app. You can't prescribe one correct behaviour. 
I think using MUST requirements where you can't write a testcase is wrong.

Possibly what's bogus in the spec is calling out specific protocols. The 
actual requirement seems to be that if a link to a protocol is activated 
that the UA doesn't understand natively, it has the ability to dispatch 
that link to a lower level in the stack e.g. the OS, to handle in some 
way. I still don't know how you would write a testcase for this though.
Received on Wednesday, 18 April 2012 12:59:42 UTC

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