Re: Test cases: invalid syntax vs. invalid semantics

On 11/04/2011 11:34, Philip Jägenstedt wrote:
> On Fri, 08 Apr 2011 11:42:56 +0200, Davy Van Deursen
> <davy.vandeursen@ugent.be> wrote:
>
>> Dear all,
>>
>> continuing the discussion from last telcon regarding the behaviour of
>> a UA in case of an invalid media fragment, let me sketch the possible
>> situations and proposal outcomes.
>>
>> 1) Invalid Syntax
>> For example, #t=3,4,4 is invalid syntax. The UA is always able to
>> detect syntax errors and thus knows that the media fragment is
>> invalid. Now, what is a UA in this case supposed to do? Two proposals
>> are on the table:
>> - the whole resource is requested by the UA (preferred by Philip and
>> Davy, see [1])
>> - the UA only requests setup information (preferred by Silvia)
>>
>>
>> 2) Invalid Semantics
>> 2a) UA is able to detect that the fragment is invalid
>> For example, #t=7,3 is semantically invalid and the UA is able to
>> detect this. Again, the same two possibilities as described above are
>> available.
>>
>> 2b) UA is not able to detect that the fragment is invalid
>> For example, #t=15,20 when the resource has a duration of 10s. When
>> the UA does not know the duration, it is not able to detect that this
>> fragment is invalid. What will the visual result be in this case? Note
>> also that it is possible in this case that the UA requests a temporal
>> range (i.e., Range: t:npt=15-20) which the server (for the moment)
>> will answer with a 416 ...
>>
>> I think we need to answer these questions in order to efficiently
>> progress with the test cases.
>
> I think that the most straightforward solution is to unify the handling
> of syntax errors and semantic errors.
>
> In particular, as part of "Processing Media Fragment URI", I think that
> we should make the parser discard things that are deemed to be
> "unsemantic". This makes it very straightforward to implement, e.g. for
> the temporal dimension after parsing #t=s,e one would simply check if s
> < e. If it is not, then that dimension is ignored, just as for syntax
> errors. We should add similar restrictions for dimensions as part of the
> "For each name-value pair" loop in section "Processing name-value lists".

This works indeed in case the UA is able to detect the error (syntax or 
semantic). However, what in case of a semantic error that is unable to 
be detected by the UA (i.e., case 2b that I sketched above)?

Best regards,

Davy

-- 
Davy Van Deursen

Ghent University - IBBT
Department of Electronics and Information Systems - Multimedia Lab
URL: http://multimedialab.elis.ugent.be/dvdeurse

Received on Monday, 11 April 2011 09:55:09 UTC