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RE: [TTML] ttm:item issues

From: John Birch <John.Birch@screensystems.tv>
Date: Tue, 16 Dec 2014 16:39:42 +0000
To: Nigel Megitt <nigel.megitt@bbc.co.uk>, Andreas Tai <tai@irt.de>, "Glenn Adams" <glenn@skynav.com>, public-tt <public-tt@w3.org>
Message-ID: <0981DC6F684DE44FBE8E2602C456E8AB016C12963E@SS-IP-EXMB-01.screensystems.tv>
Re: 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).

Actually I'm not sure this is my point! (I guess I didn't make it very well ;-)

What I'm trying to get across is that if TTML 2.0 goes down the route of providing a *common metadata mechanism* that can be utilised by derived standards (like SMPTE, EBU etc.), then it might be worth considering if TTML2.0 should 'recommend' using a single place where metadata labels (and their semantics) are registered... to avoid duplication or contradiction of metadata items in derived standards with similar or identical names. E.g. by using http://metadataregistry.org/

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P Before printing, think about the environment-----Original Message-----
From: Nigel Megitt [mailto:nigel.megitt@bbc.co.uk]
Sent: 16 December 2014 10:46
To: Andreas Tai; Glenn Adams; public-tt
Subject: [TTML] ttm:item issues

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.


[1] Andreas's email re ttm:item

[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

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Received on Tuesday, 16 December 2014 16:40:19 UTC

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