W3C home > Mailing lists > Public > public-tt@w3.org > December 2014

[TTML] ttm:item issues

From: Nigel Megitt <nigel.megitt@bbc.co.uk>
Date: Tue, 16 Dec 2014 10:45:34 +0000
To: Andreas Tai <tai@irt.de>, Glenn Adams <glenn@skynav.com>, public-tt <public-tt@w3.org>
Message-ID: <D0B5BDC6.182DC%nigel.megitt@bbc.co.uk>
In last week's TTWG meeting our goal was to close a number of issues on
TTML2, but we were unable to close any of those whose solutions were based
on ttm:item as a solution, due to lack of clear consensus following
Andreas's email [1]. Those are issues 244, 245, 246, 247, 248, 249, 250,
289, 290, 291 and 292 in the tracker.

I would like us to be able to close those issues by the end of this week's
meeting.

Outstanding questions
=====================

The three raised points are:

_____________________
1) Do we have a hard requirement that every document be validatable using
XML Schema 1.0? Can documents be validated using XML Schema at all?

The closest I can find to the requirement is in [2], requirement R604. In
any case, there's nothing that demands a particular schema validation
technique or version.

Also, note that R601 specifies that individual metadata items should have
both name and type as well as value, and the current solution omits type.
Possibly the addition of an optional type attribute would facilitate
validation, using assertions in XML Schema 1.1, of the flavour:

   <xs:assertion test="every $v in //ttm:item[@type='xs:positiveInteger']
satisfies ($v = xs:positiveInteger($v))"/>

i.e. verify that all ttm:items that have a type attribute whose value is
xs:positiveInteger contain data that can be passed to the constructor for
an xs:positiveInteger without raising an error [3], and after casting,
have the same value (to return true even if the value is zero).

Would this (addition of the type attribute) address the problem raised?

_____________________
2) Should we integrate foreign namespace metadata elements directly in the
spec?

As far as I can tell, integrating XML from other namespaces is already
permitted and does not need to be specified to be permitted.
Glenn raised the point that circular references between specs need to be
avoided too. 
John raised the point that in some cases it would be useful for TTWG to
express a preference for some metadata "names" (including classification
schemes).

It seems to me that this question does not need to be resolved prior to
closing the ttm:item issues - does anyone disagree?


_____________________

3) Should classification scheme be separable from item name?

As indicated this is syntactic sugar. For me, though it is nice to have, I
would not block closure of the ttm:item issues on this basis.


_____________________

Nobody has raised any other reasons not to close the relevant issues.



References
----------

[1] Andreas's email re ttm:item
http://lists.w3.org/Archives/Public/public-tt/2014Dec/0012.html

[2] TTML Requirements http://www.w3.org/TR/2006/NOTE-ttaf1-req-20060427/

[3] Xpath functions constructor for XSD types
http://www.w3.org/TR/xpath-functions/#constructor-functions-for-xsd-types


Received on Tuesday, 16 December 2014 10:46:06 UTC

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