Subject: Re: [sipcore] Extensions to the reg event package

From: "Worley, Dale R (Dale)" <[email-masked]>
Date: Fri, 17 Dec 2010 12:01:00 -0500

> From: Thomson, Martin [[email-masked]]
> 
> In practice, a processor that uses the original schema definitions is
> likely to reject a document that uses the modified structure.
> 
> For instance, the original might define (A, B, *) where * is an
> extension point, and the extension defines (A, B, C, *).  Because if
> the way that * is defined, it means anything not in this namespace.
> If the original sees C, which claims to be in the same namespace, it
> rejects it.

Then, to phrase it another way, schemas are extensible in that
elements of other namespaces may be inserted, but not new elements of
the existing namespace.

> The size of namespace declarations is a common source of complaints.
> The usual response is to point folks at ASN.1+?ER.  I wouldn't dream
> of being so rude.

The DER and PER encodings do seem to be much denser, but I don't see
any mechanism for extensibility.  XER seems to be essentially what
we're already doing.

Dale