Re: ASN-1 - XCBF Liaison?

[John Larmouth <j.larmouth@salford.ac.uk>]

Phillip H. Griffin wrote:
> John,
> 
> I do not have a clue what you mean when you use the term
> "EXTENDED-XER". I can find no mention of this term in
> any of the ASN.1 standards that XCBF and X9.84 reference.

EXTENDED-XER is what was earlier referred to as VXER (Variant XER). 
That is just a name change.  Use of it allows encoding instructions to 
be applied (without an encoding instruction it does not differ from 
BASIC-XER - the new name for what you would call XER).  A single 
encoding instruction can modify many of the XER encodings to use text 
rather than empty element tags, to provide better alignment with XSD 
encodings.  There are also about 20 specific encoding instructions such 
as BASE64 that perform specific functions in relation to XML encodings.

Probably the most important such encoding instruction is UNTAGGED, that 
removes XML tags round things like a sequence of elements, or a choice 
of alternatives, or a sequence of elements, but there are others that 
are designed to support XSD-specific functionality, such as 
DEFAULT-FOR-EMPTY and USE-TYPE and USE-NIL and USE-ORDER.  Mainly, but 
not exclusively, the encoding instructions have been developed to 
support the mapping from XSD, and apart from BASE64, are probably not of 
particular relevance to the XCBF work.

John L