Fragments by Reference rather than Value

Dear all,

It's great to see that the Media Fragments specification is stabilizing, and
to hear at WWW2010 that there is a commitment to extensibility.

As mentioned at WWW2010, we have many use cases for media fragments that are
not amenable to inclusion by value within the URI.  For example, a long SVG
path might be used to express a non rectangular area within an image, and
possibly in a time series in order to have a moving area within a video.
Equally non "traditional" web resources can benefit from this approach, such
as 3d objects or scenes, database slices and so forth.

The proposal which we suggested last October was to add a new type of
fragment, which has a URI as its value.  This URI can then be dereferenced
and interpreted in the context of the base resource.  For example, an image
with an SVG overlay fragment might be:

http://www.example.com/imgs/img1.jpg#ref=http://www.example.com/fragments/frag1.svg

This is a no-fuss way to include unlimited extensibility as the standard
does not have to specify the contents of the resource being pointed to.  It
adds at most a single section to the document and no significant barriers to
understanding.

The original objection of being able to non rectangular images being
technically impossible seems to be unfounded, given the presentation at
WWW2010 at least which demonstrated a possible rendering of a video where
the fragment area was highlighted, rather than generating a completely new
resource.


Many thanks for your consideration!


Rob Sanderson (for the OAC project, http://www.openannotation.org/)