Re: [opendocument-users] Harmonization with IS 29500-3:2008 Marcup Compatibility and Extensibility

[John Cowan <cowan@ccil.org>]

marbux scripsit:

> I'd also like to see some clarification of circumstances where the
> MustUnderstand attribute's use is warranted. This is the only MCE
> compatibility attribute that has a mandatory requirement, the
> must-abort-document-processing-if-you-don't-understand requirement.
> There is room for potential abuse if left unclarified.

There is indeed.  I'd recommend that a profile of 29500-3 that excludes
MustUnderstand be prepared for ODF purposes.

The semantics of the feature obviously come from SOAP, where it makes
some sense for a client to say to a server, "If you cannot handle this
part of my request, don't do anything rather than doing the wrong thing."
But the producer and consumer of an office document don't stand in the
master and servant relationship: the producer lays down the document
for the consumer to do with whatever he wishes to (or is able to).

> E.g., as written, a vendor could simply slap that attribute on all
> extensions whether warranted or not to create interoperability
> barriers for the competition, whose implementations would be
> non-conformant if they ignored the attribute and processed the markup
> anyway. I.e., what to do when an implementation does not *completely*
> understand the markup but enough is known to make some sense of it
> after consulting which vendor's namespace the questionable markup
> resides in?

If you look at the definitions in clause 3, you can see that the
definition of "understanding" has nothing semantic about it.  A namespace
is "understood" if at least one element or attribute is "recognized",
and an element or attribute is "recognized" if the consumer is able to
identify it using the schema to which the document supposedly conforms;
and of course you cannot do this unless you actually have the schema!

So "understanding" is a rather weak notion: even a very stupid consumer,
such as one which only knows how to count the paragraphs in a document,
should be able to "understand" any number of namespaces, whether they
are flagged with MustUnderstand or not.  Consequently, MustUnderstand
will not do what document producers think it will do, which is all the
more reason not to allow it in ODF.

-- 
I am expressing my opinion.  When my            John Cowan
honorable and gallant friend is called,         cowan@ccil.org
he will express his opinion.  This is           http://www.ccil.org/~cowan
the process which we call Debate.                   --Winston Churchill