Re: [MMUSIC] File transfer issue 49: multipart/mixed or multipart/related

[Paul Kyzivat <pkyzivat at cisco.com>]

Miguel Garcia wrote:
> During the last IETF meeting there was a comment with respect the 
> relation of SDP bodies and icon bodies.
>
> When the two bodies appear together, the draft says they need to be 
> wrapped in a MIME multipart/mixed container. Adam commented that it 
> should be multipart/related instead.
>
> RFC 2387 defines the multipart/related MIME wrapper:
>
>    The Multipart/Related media type is intended for compound objects
>    consisting of several inter-related body parts.  For a
>    Multipart/Related object, proper display cannot be achieved by
>    individually displaying the constituent body parts.
>
> RFC 2046 defines the multipart/mixed MIME wrapper:
>
>    The "mixed" subtype of "multipart" is intended for use when the body
>    parts are independent and need to be bundled in a particular order.
>    Any "multipart" subtypes that an implementation does not recognize
>    must be treated as being of subtype "mixed".
>
>
> The difference between both is subtle, in my opinion. The 
> multipart/related definition says that "proper display cannot be 
> achieved by individually displayign the constituent body parts", which 
> is not entirely true: SDP will be meaningful in the absence of an icon; 
> the icon is also meaningful isolated, although it is not linked to any 
> file descriptor.

I agree that in this case the parts don't seem to be related.

> The multipart/mixed definition speaks about "independent parts that need 
> to be bundled in a particular order", which is probably true, because 
> although the SDP and the icon are independent, the SDP should be read 
> first.

I don't see any ordering requirement here. There are certainly other 
cases where mixed seems to be the thing to use where ordering definitely 
isn't important.

Is there another multipart subtype that is like mixed except without 
ordering? (multipart/unordered?) I've not heard of such a thing. If not 
it seems that mixed must be used even when ordering isn't important.

> While I don't have a strong opinion, I would suggest to leave the draft 
> with the current indication of multipart/mixed.

I agree unless there is a choice better than mixed or related.

	Paul

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