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Re: ISSUE-3: Does our MF URI syntax imply that we need to update MIME Type registrations?

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Thu, 29 Jan 2009 05:59:29 +1100
Message-ID: <2c0e02830901281059x39b64815x35620abbfecb3b3c@mail.gmail.com>
To: RaphaŽl Troncy <Raphael.Troncy@cwi.nl>
Cc: Media Fragment <public-media-fragment@w3.org>

On Thu, Jan 29, 2009 at 12:47 AM, RaphaŽl Troncy <Raphael.Troncy@cwi.nl> wrote:
>
> ISSUE-3: Does our MF URI syntax imply that we need to update MIME Type
> registrations?
>
> http://www.w3.org/2008/WebVideo/Fragments/tracker/issues/3
> Raised by: Michael Hausenblas
>
> In [1] Michael argued that whenever we talk about URI semantics, we need to
> start with RFC3986 section 3.5:
>
> 'The semantics of a fragment identifier are defined by the set of
> representations that might result from a retrieval action on the primary
> resource. The fragment's format and resolution is therefore dependent on the
> media type [RFC2046] of a potentially retrieved representation, even
> though such a retrieval is only performed if the URI is dereferenced. If
> no such representation exists, then the semantics of the fragment are
> considered unknown and are effectively unconstrained. Fragment identifier
> semantics are independent of the URI scheme and thus cannot be
> redefined by scheme specifications.'
>
> Further, from RFC2046 we learn that the MIME Type Registrations (taking a
> JPG still image as an example) for JPEG 2000 (ISO/IEC15444) is specified in
> RFC3745 where no fragments are defined, hence the general rules from RFC3986
> apply.
>
> Do we need to update all registries of targeted media types or are we fine
> with sticking to the fallback rule from RFC3986 ('If no such representation
> exists, then the semantics of the fragment are considered unknown and are
> effectively unconstrained.')?

I'm glad we discussed this yesterday and I finally understood the
particular issue that Michael was addressing.

Just for the record: my suggestion went along the following lines.

We have no authority to update registries of targeted media types. As
far as we know there are only few media types that actually have a
registered fragment specification - these include Ogg, MPEG-4, and
MPEG-21 - for all others, the semantics of the fragment are considered
unknown. The media fragment specification to be defined through the
Media Fragment WG will be a recommendation to media type owners. We
recommend to update or add the fragment semantics specification to
their media type registration once a generic scheme has been
determined. At minimum, those schemes that have an existing, diverging
fragment specification should be harmonised. To achieve uptake of the
scheme, updates to the server and client software for the different
media types will be required.

Cheers,
Silvia.
Received on Wednesday, 28 January 2009 19:00:05 GMT

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