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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.

Received on Thursday, 1 July 2010 12:39:57 UTC

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