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Answer to Ian Hickson: Additions to error mechanism section

From: Karl Dubost <karl@w3.org>
Date: Tue, 3 May 2005 11:45:34 -0400
Message-Id: <C8CA19B6-CBD8-4061-9213-F5794DA2622D@w3.org>
Cc: Ian Hickson <ian@hixie.ch>
To: www-qa@w3.org

Dear Ian,

Thanks for your comments on the Last Call version of the QA Framework:
Specification Guidelines[0] - 22 November 2004

After two weeks from now (on May 18, 2005), the lack of answer will  
be considered as if you had accepted the comment.

Original comment (issue 1047 [1])
http://lists.w3.org/Archives/Public/www-qa/2005Jan/0012.html
Thank you for your comment, which the QA Working Group has accepted.   
We have reworded the affected section as you recommended and it now  
reads [2]

“What does this mean? For each class of product affected by an error  
condition, include error-handling instructions for when an extension  
is not available or understood.

Why care? When using a strict conforming application, users might  
have to deal with documents, data considered invalid because they  
contain errors, or extended syntactically. Developers need to know  
what is the expected behavior of the application in such context.

Techniques
There are typically two approaches: (see section 4.2.3 Extensibility  
from Architecture of the World Wide Web, Volume One [WEB-ARCH])
a so-called “must Understand” policy, as implemented in SOAP 1.2 by  
the mustUnderstand attribute; in this type of mechanism, a processor  
encountering a syntax token not defined in the specification is  
required to know how to process the said token or must fail for the  
whole unit where the token appears
a so called “must Ignore” policy (as implemented in SOAP 1.2 by the  
mustIgnore attribute), where a processor not knowing how to process  
an unknown syntax token must skip part or the totality of the unit  
where the token appears
A good way to handle these two approaches is to have a way in the  
syntax to distinguish which behavior is expected (e.g.,  
mustUnderstand/mustIgnore attributes in SOAP 1.2). Which policy to  
choose depends heavily on the importance of the processing of the  
data, the user experience of applications based on the said format, etc.
Do not forget to address all the classes of products. For example, an  
authoring tool and a rendering tool might behave in different ways.”


[0] http://www.w3.org/TR/2004/WD-qaframe-spec-20041122/
[1] http://www.w3.org/Bugs/Public/show_bug.cgi?id=1047
[2] http://www.w3.org/TR/2005/WD-qaframe-spec-20050428/#define-error-gp


-- 
Karl Dubost
QA Working Group Chair
http://www.w3.org/QA/WG/
Received on Tuesday, 3 May 2005 15:45:50 UTC

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