Re: Media Fragments URI parsing: pseudo algorithm code

On Mon, 28 Jun 2010, Philip Jägenstedt wrote:

> On Wed, 16 Jun 2010 14:42:03 +0200, Raphaël Troncy 
> <raphael.troncy@eurecom.fr> wrote:
>
>> Dear Philip,
>> 
>> We have discussed today during the face to face meeting of the WG the 
>> content of the section 4.1.1 and 4.1.2 that you wrote, regarding a pseudo 
>> code algorithm example of how to process media fragments URI, see also 
>> http://www.w3.org/2010/06/16-mediafrag-minutes.html#item07 though very 
>> little has been scribed.
>> 
>> We have decided to move this 2 subsections in a new Annex D - Notes on 
>> parsing Media Fragments URI.
>> 
>> The rationale is that this piece of text is informative, the ABNF syntax 
>> being normative. The WG believe that the ABNF is self-contained for 
>> implementers to use the right grammar tools to perform optimally the URI 
>> syntax.
>> Please let us know if you disagree with this decision.
>>
>>   Erik & Raphaël
>> 
>
> Hi all,
>
> I've been on vacation getting married, so sorry for my tardy reply.
>
> This is the version I'm looking at: 
> http://www.w3.org/TR/2010/WD-media-frags-20100624/
>
> There's syntax and processing on two levels here.
>
> 1. name-value pairs delimited by "&" and "=".
>
> 2. syntax of the names and values of the four different dimensions, e.g. 
> timeprefix and timeparam for the time dimension.
>
> I do disagree with the change, because it leaves the spec without any 
> normative requirements for how to parse level 1. The only thing we have is 
> the non-normative segment/mediasegment and related productions in 
> <http://www.w3.org/TR/2010/WD-media-frags-20100624/#collected-syntax-uri>. 
> Apart from being non-normative, it is also incorrect as it doesn't capture 
> the fact that any names and values of name-value pairs can be %-encoded, e.g. 
> as in "%74=%6ept%3A%310". That definition doesn't appear anywhere in the 
> normative text and should be removed.
>
> If I am missing it, please point out which ABNF normatively defines the 
> syntax for level 1: name-value pairs delimited by "&" and "=".

The ABNF describe the whole syntax, and then the different parts. There is 
no need for a multi-step parsing scheme requiring to re-read multiple time 
the same bytes.
To me "%74=%6ept%3A%310" is not a media fragment. %-escaped values are 
allowed only where they are allowed (see grammar).

> As for level 2, we have all the ABNF syntax productions, but nothing that 
> binds them together, as D.2 Processing name-value lists does (did). I would 
> be happy to see that replaced by a more strict definition achieving the same 
> thing, or failing that, making D.2 normative again.
>
> I will continue to bring up the issue of well-defined processing until it is 
> resolved. MF is a small spec and it's not difficult to define achieve 
> interoperability. That means that it should be possible for two different 
> implementors to read the spec and implement two different parsers that have 
> the exact same result for all possible input, valid or not. Without that, the 
> spec shouldn't progress to Last Call. As usual, I don't care much what spec 
> writing style is used to achieve this, as long as it is achieved.
>
>

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

         ~~Yves

Received on Tuesday, 29 June 2010 20:30:37 UTC