Re: [T2TRG] CoRAL Dictionaries and the side meeting yesterday

[Klaus Hartke <[e-mail]>]

Hi Jim!

Jim Schaad wrote:

> I am still having some problems with the way that you described how
> dictionaries would work for CoRE apps with a single dictionary being used.
>

That may be because the current idea is not described well enough yet and
because there is a problem with it. Let me try to explain. I’m very open to
suggestions.

My understanding of what you said is that:
> 1.  We would define a CoRE apps dictionary and pre-populate it with some of
> the common items
> 2.  For each new CoRE app created (by the IETF?) the dictionary will be
> extended by adding the new items to the dictionary (maybe the end, maybe
> later)
>

Yes. The current idea is to have one dictionary that is shared by all CoRE
apps defined by the IETF and that is maintained as an IANA registry.

The assumption here seems to be that a CoRE app would never be extended with
> new things.  As an example of what I mean consider the following:
>
> *  Given the intense pressure from the ACE working group, the CoRE WG gets
> it act together and releases a version 1 Pub-Sub server.
> * So a client and a server are released which use the dictionary for
> compression and are both happy.
> *  A version 2 of the Pub-Sub server gets released.  This adds some
> vocabulary around wills.  The vocabulary is then added to the CoRE App
> dictionary
> *  The Pub-Sub server gets updated because it is a big box, but the client
> does not because it is small
> *  The client queries the Pub-Sub server and gets back some compression
> points which it does not recognize.
>

This is exactly the current idea how you would evolve a CoRE app.

What am I missing?
>

Assume for a moment that the V1 client could decompress the compression
point. Then it still wouldn't recognize the wills-related vocabulary,
because that’s a V2 feature. However, it can still make sense out of all
the other vocabulary, so the V1 client is still interoperable with the V2
server. No problem here.
We’ve got a problem, though, when a V2 client understands the wills-related
vocabulary, but doesn’t know the compression points for it (because they
may have been added to the dictionary much later than the V2 specification
was released). I don’t know how to solve that at the moment.

Klaus