Subject: RE: [Simple] IMDN Issue 1: Message/CPIM namespace for extension headers

From: "Burger, Eric" <[email-masked]>
Date: Thu, 3 Aug 2006 12:33:41 -0400

I agree with Ben here; my interpretation of RFC 3862 is the
*interpretation* of namespaces is optional.  If we went the route below,
we would have to modify the cpim-headers IANA registry.  Not hard or
impossible, but setting a bad precedent, unless the goal is to show no
one uses name spaces so that we can take them out for DS.  [being
facetious...]

-----Original Message-----
From: Ben Campbell [mailto:[email-masked]] 
Sent: Monday, July 31, 2006 9:29 AM

Even without capablity negotiation, the presence of a namespace can  
be useful from an implementation perspective. For example, If I do  
not see the "IMDN" namespace, I do not have to bother looking for  
IMDN related headers  headers.

Also, section 3.4 of IET 3862 says the following:

>
>    NOTE: This section defines a framework for header extensibility  
> whose
>    use is optional.  If no header extensions are allowed by an
>    application then these structures may never be used.

I read that to mean that, in spirit, the "optionality" of supporting  
namespaces is contingent on not supporting any extensions. This is  
certainly an extension. But then, the IANA registry does allow  
extensions without namespaces. I'd be curious to hear the opinions of  
the RFC3862 authors on this.

-----Original Message-----
From: Hisham Khartabil [mailto:[email-masked]] 
Sent: Wednesday, August 02, 2006 3:13 AM
To: [email-masked]' WG
Cc: [email-masked]; [email-masked]
Subject: [Simple] IMDN Issue 1: Message/CPIM namespace for extension
headers

RFC3862 ((CPIM): Message Format) defines a framework for header 
extensibility whose use is optional. At least that's how it is 
understood by some of us in that the default namespace can be used and 
no need for a new namespace. Others believe that it is mandatory to 
define a new namespace for Message/CPIM header extensions. We seek 
guidance from the authors of RFC3862 on that.

Depending on the outcome to the above question, we may need to make the 
decision regarding the need of the new namespace. Some argued that it 
is useful for capability negotiation. "What capability negotiation?" 
was my response.

Comments and guidance are welcome.

Regards,
Hisham

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---

From: Hisham Khartabil <[email-masked]>
Date: Tue, 8 Aug 2006 12:00:40 +0200

Well, the authors of the RFC are not commenting. Maybe the ADs can help.

The RFC says:

"If no header extensions are allowed by an
    application then these structures may never be used."

To me, this means that if IMDN RFC does not allow header extensions, 
then we don't need a namespace. As far as I can tell, we are not 
allowing or don't need to allow new header extensions.

The RFC also says

"The Message/CPIM media type registration designates a default
    namespace for any headers that are not more explicitly associated
    with any namespace.  In most cases, this default namespace is all
    that is needed."

This is more proof that we don't need a new namespace.

I really don't want to make the message be more complicated and larger 
for no good reason.

Hisham

---

From: Derek Atkins <[email-masked]>
Date: Tue, 08 Aug 2006 14:47:03 -0400

Sorry for my late reply..  I've been dealing with family issues.

My belief is that the optional use of namespaces is contingent on
the optional use of header extensions.  If, however, you support
header extensions then you must support namespaces.  This is the
interpretation that I believe Ben holds.

I don't understand the specific background of your usage requirements,
but if you want to define application-specific headers then you should
use header extensions, which implies using a namespace.

I hope this helps,

-derek

-- 
       Derek Atkins                 617-623-3745
       [email-masked]             www.ihtfp.com
       Computer and Internet Security Consultant

---

From: Hisham Khartabil <[email-masked]>
Date: Tue, 8 Aug 2006 21:19:49 +0200

Hi Derek,

Apologies for not giving you the background you need.

We are defining Instant Messaging Disposition Notifications (IMDN). The 
disposition notification information will be carried in the body of a 
CPIM message.

In the Instant Message itself, we need new CPIM headers to carry the 
IMDN request for that IM along with information about how to route the 
IMDN back, amongst other meta date. In the IMDN itself, we need CPIM 
headers to carry information about how to route the IMDN back to the IM 
sender.

Do you believe we need to create a new namespace to define those 
headers? or can we just use the default namespace? I do not anticipate 
that we need to allow more extension headers for this application.

I guess those headers are application specific so you believe we need a 
namespace, but I just want to make sure.

Thanks,
Hisham

---

From: Graham Klyne <[email-masked]>
Date: Tue, 08 Aug 2006 22:26:07 +0100

Hi guys,

My apologies for not participating sooner, but the earlier messages don't seem
to have reached my notice. (Probably overlooked in the oceans of spam - sorry!)

The extensibility mechanism is based on XML namespaces, which in principle
allows document formats that can be arbitrarily (and privately) through the
introduction of new namespaces, without fear of introducing a name clash.
Drawing upon that for precedent, my take would be that if you want to introduce
a new header field within the CPIM namespace that would imply an update to the
CPIM format standard, and as such should be dealt with through the normal
procedures for doing that.

On closer examination, I see this is borne out by RFC3862, which defines a URN
sub-namespace (urn:ietf:params:cpim-headers), and requires for values in this
namespace "Additional values may be defined by standards track RFCs that update
or obsolete RFC 3862." (RFC3862, section 7.2).

This should be read in conjunction with section 4: "all headers defined here are
associated with the namespace uri <urn:ietf:params:cpim-headers:>", and section
6: "As defined, the 'Message/CPIM' content type uses a default namespace URI
'urn:ietf:params-cpim-headers:', and does not define any other implicit
namespace prefixes."

Does this answer your query?

#g
--

-- 
Graham Klyne
For email:
http://www.ninebynine.org/#Contact

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From: Hisham Khartabil <[email-masked]>
Date: Wed, 9 Aug 2006 09:35:05 +0200

Yes it does. I will define a new namespace for IMDN since we are not 
*updating* RFC3862.

Thanks,
Hisham