Draft Proposed Answer to Ian Hickson: Additions to error mechanis m section

Original comment (issue 1047 [1])

http://lists.w3.org/Archives/Public/www-qa/2005Jan/0012.html
<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
<http://www.w3.org/TR/2004/REC-webarch-20041215/#extensibility> 4.2.3
Extensibility from Architecture of the World Wide Web, Volume One [
<http://www.w3.org/TR/2005/WD-qaframe-spec-20050428/#WEB-ARCH#WEB-ARCH>
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."

 

 

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