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Re: Media Fragments URI parsing: pseudo algorithm code

From: Yves Lafon <ylafon@w3.org>
Date: Thu, 1 Jul 2010 08:39:51 -0400 (EDT)
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
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>
Message-ID: <alpine.DEB.1.10.1007010838180.31115@wnl.j3.bet>
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).


-- 
Baroula que barouleras, au tiéu toujou t'entourneras.

         ~~Yves
Received on Thursday, 1 July 2010 12:39:57 GMT

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