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Re: Media Fragments URI parsing: pseudo algorithm code

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Thu, 1 Jul 2010 20:43:12 +1000
Message-ID: <AANLkTinEvaizugXrRkKSRQ6ktPEgGzKgGCn0TlUQFpUZ@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 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!

Cheers,
Silvia.
Received on Thursday, 1 July 2010 10:44:04 GMT

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