[Ace] Embedded Content Types

[Jim Schaad <[e-mail]>]

The CoRE working had an interesting virtual meeting this morning (my time)
where the main topic of discussion was how to deal with embedded content
types.  This is a current problem that needs to be addressed with the EST
document which is currently trying to deal with last call comments.  The log
from the meeting can be found at
https://etherpad.tools.ietf.org/p/core-interim-2019-02-20.

The takeaway from this that I got was:
1.  There is a real problem and we need to figure out the best ways to try
and deal with this in a generic manner.   This is a problem not only here,
but it the Publish/Subscribe CoRE document and in many other cases that we
can see.

2.  We are not going to get a general solution immediately so EST needs to
look at  doing something now.

3.  A couple of different possibilities where discussed that could be used:
a)  Return a list of links rather than a multipart content and let the
client sort through that list and download the things that they want.  This
is a purely reactive solution.
b) Use a different URI to ask for the different options.  This could be done
either by the use of a different URI path or by the use of a query
parameter.
c) Register a different content type for each of the possible return values.

There was a general preference for the use of a different URI as being the
solution that should be used today.  The idea of registering multiple
content types was generally disliked as it does not really extend well.
There was no specific preference on whether the use of a different URI path
or a query parameter would be preferred.  The use of a different URI would
allow for better discovery of capabilities.  

The idea of listing nested content types in the 'ct' link type was also
universally disliked.

The CoRE, T2TRG and other forums are expected to continue discussions on
this topic in different contexts such as Pub-Sub and CoRAL. To come up with
both proactive and reactive solutions to the more general problem.

Jim