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RE: Default Semantics, Banana Elements, and Versioning

From: David Orchard <dorchard@bea.com>
Date: Tue, 4 Sep 2007 17:00:05 -0700
Message-ID: <BEBB9CBE66B372469E93FFDE3EDC493EAB9BAD@repbex01.amer.bea.com>
To: <noah_mendelsohn@us.ibm.com>, <www-tag@w3.org>
Excellent idea.  The Terminology Draft of July 4th has the banana
example at http://www.w3.org/2001/tag/doc/versioning#iddiv377685352
Further, it takes the example one more step and covers the scenario of
where PHTML is versioned to include the banana element into a PHTML2.
This is somewhat of a tortured analysis because the compatibility story
depends upon the content model of <BANANA>, such as whether it can
contain <PHTML>, <HEAD>, or <BODY> elements and covers both allow and
disallow cases.


	From: www-tag-request@w3.org [mailto:www-tag-request@w3.org] On
Behalf Of noah_mendelsohn@us.ibm.com
	Sent: Tuesday, September 04, 2007 4:48 PM
	To: www-tag@w3.org
	Subject: Default Semantics, Banana Elements, and Versioning

	First a caveat:  I have not yet read Dave's new drafts on
versioning.  I'm hoping to do so on the plane on Sunday night, so this
is not a comment on them. 
	Anyway, I see that we are planning to have some discussion of
Versioning at the upcoming F2F meeting in Southampton, and I wanted to
remind everyone of the issues that I summarized in [1], which has as its
subject "Defined Sets, Accept Sets, and Banana Elements."  I hope we can
spend a bit of time at the F2F exploring these issues, and getting
comfortable (or not) with how our drafts address them. 
	As a reminder, [1] explores in detail a use case I raised at the
Google F2F, and sets out what I understood to be Tim BL's analysis of
it.  In short, the issue centers around HTML-like languages and
instances such as: 
	            <BANANA>Versioning is hard.</BANANA> 
	We assume that the PHTML spec V1 says nothing special about
<BANANA> elements, except that like all other tags not explicitly named,
they are to be ignored, but with one exception.  Other languages, such
as CSS, are not prohibited from discovering their presence, so: 
	        BANANA {font-weight:bold} 
	will cause "Versioning is hard" to be boldfaced.  Furthermore.
We may assume that some future version of PHTML, say V2, provides an
explicit semantic for <BANANA>, perhaps indicating that it causes
content to be rendered in parenthesis: 
	        (Versioning is hard.) 
	My question is: what do our defined-set/accept-set models
provide to explain the evolution of PHTML from V1 to V2?   If I
understood Tim correctly (see [1]), his view is that even documents with
<BANANA> are in the defined set for the combined language PHTML V1+CSS.
That makes sense, insofar as we've shown that the presence of the
<BANANA>'s can't be ignored.  What concerns me is that this seems to
imply that our model adds very little value to any versioning system in
which the default semantic is not: ignore completely.  What does this
architecture say is happening when PHTML V2 comes out?  All the
documents are in the defined sets of all language versions.  How does
that help us? 
	So, with the caveat that I'd like to read Dave's drafts to see
what they say (I know he said he was picking up some stuff from my
earlier notes), I'd like to suggest that we discuss this question a bit
at the F2F.  The reason I keep raising this is that I think it's common,
perhaps the norm, for languages to have semantics other than "ignore
completely" even for the content that they don't specify in detail.  On
a purchase order, you'll probably find a way to print the fields that
you don't otherwise understand.  Almost surely you'll store them in your
database, and probably you'll apply digital signatures to them.  We've
already seen that in the presence of CSS, every possible element can
contribute to the rendering of an HTML document -- does that the
presence of CSS prevents us from explaining that something very
interesting happens when a new version of HTML provides explicit
semantics for, say <BANANA>?   I think this is all very important. 
	Noah Mendelsohn 
	IBM Corporation
	One Rogers Street
	Cambridge, MA 02142
Received on Wednesday, 5 September 2007 00:00:36 UTC

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