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Re: Media Fragments URI parsing: pseudo algorithm code

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Thu, 1 Jul 2010 22:49:02 +1000
Message-ID: <AANLkTing3HfNFIZIMy2IZGNYb7lnaaqBdQtpxz7yLW1A@mail.gmail.com>
To: Yves Lafon <ylafon@w3.org>
Cc: Philip Jägenstedt <philipj@opera.com>, Jack Jansen <Jack.Jansen@cwi.nl>, Raphaël Troncy <raphael.troncy@eurecom.fr>, Media Fragment <public-media-fragment@w3.org>
On Thu, Jul 1, 2010 at 10:39 PM, Yves Lafon <ylafon@w3.org> wrote:
> On Thu, 1 Jul 2010, Silvia Pfeiffer wrote:
>> On Thu, Jul 1, 2010 at 7:10 PM, Yves Lafon <ylafon@w3.org> wrote:
>>> On Wed, 30 Jun 2010, Philip Jägenstedt wrote:
>>>> On Wed, 30 Jun 2010 16:22:15 +0200, Yves Lafon <ylafon@w3.org> wrote:
>>>>> On Wed, 30 Jun 2010, Philip Jägenstedt wrote:
>>>>>> You cannot write a robust MF parser based on this grammar, because
>>>>>> t=1&foo=bar is not a valid production, meaning that any future
>>>>>> extension foo
>>>>>> of MF will cause that parser to fail completely. Either the grammar
>>>>>> itself
>>>>>> must be relaxed, or the parsing must be defined normatively and handle
>>>>>> some
>>>>>> things which are not valid productions of the grammar.
>>>>> What do you mean by "robust" ?
>>>> I mean that it doesn't stop working completely for future additions to
>>>> the
>>>> syntax, that it should degrade gracefully. If browsers shipped with a
>>>> parser
>>> Graceful degrdation should not be mistaken with "betraying intent", while
>>> graceful degradation is wonderful in many cases, you always have to be
>>> careful.
>>> ex: http://www.example.com/football.movie?xywh=10,20,30,40&action=track
>>> may
>>> mean "highlight this part (a ball), and track it", a MF aware client will
>>> just crop the identified part. That's not graceful degradation, that is
>>> betraying intent (regardless of the fact that the extra action=track
>>> might
>>> be a bad design).
>>> In CSS, properties with unknown values are ignored, to allow both
>>> graceful
>>> degradation (it doesn't impact _other_ properties) and forbid betraying
>>> intent.
>> Note that this is a URI query, so not much relevant anyway, since it
>> is up to the server to decide what to do with it.
>> However, assuming you meant
>> http://www.example.com/football.movie#xywh=10,20,30,40&action=track ,
>> I would agree with the CSS approach. If I am a UA that doesn't know
>> what to do with action=track, then I will ignore that part of the
>> fragment's name-value pairs and only interpret the first part. If that
>> results in giving a cropped video and nothing else, then that is fine.
>> It is better than ignoring all the name-value pairs and downloading
>> the full movie!
> No you are not, because you are misinterpreting action=track that still
> means "download the whole thing, but highlight only that moving region of
> the picture" (I made the difference between highlighting and cropping
> especially to demonstrate the issue).

I was wrong in saying it would "download the whole thing falsely",
since that's actually the right thing to do for interpreting only the
spatial region. Whether the UA later just presents the cropped region
or highlights the section is up to the UA. The "action=track" is still
ignored and that is the right thing to do IMO.

Received on Thursday, 1 July 2010 12:49:56 UTC

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