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RE: ASN.1 is an XML Schema Language (Fix those lists!) and Bin

asn.1 e xer
Robin Berjon wrote:
> There's a lot to say in favour of minimizing the 
> number of concrete syntaxes, and that's where a 
> lot of the concerns about having *two*  (just two!) 
> universal formats came from at the binary infosets 
> workshop. 
	The number of syntaxes isn't important. The only important
question is: "Can two systems interoperate?" Well, even if there are
hundreds of alternative syntaxes, you can always answer "Yes" to that
question by simply making a rule: "Text-based XML must always be
supported. All other encodings are optional." This allows "Dual
encoding" systems (systems that support both text-based XML and binary
encodings to interoperate with *any* other system. 
	It also means that 20 years from now, when someone comes up
with some amazing new syntax, my ASN.1 based system will be able to
communicate with it by simply changing encoding rules, not abstract
syntax. Just as the ASN.1 modules that I wrote back in the early 80's,
in a very different world, can be used virtually unchanged today to
generate valid XML. If I had defined those old modules in a concrete
syntax, I would have to rewrite program logic today, not simply link
in the E-XER encoding rules...

> The ASN.1 equivalent of a simple XML parser in terms of 
> universality would have to properly decode (and likely 
> handle negotiation for) BER, PER, CER, DER, XER, and 
> probably LWER, OER, and SER. That's a bit of a 
> behemoth to implement!
	It may be hard to implement, however, it has been done -- at
least for BER, PER, CER, DER, XER, CXER, and E-XER... At least by the
commercial suppliers like OSS Nokalva. Once X.694 was finalized, the
ambiguities and difficulties related to generating the XML encoders
were pretty much eliminated. The result is that the ASN.1 suites can
now handle all these encodings with little effort. Yes, building an
open source equivelant would be a challenge... But, it is just a
question of being "hard." At least there aren't any patent issues like
there are with something like "binXML" or the other binary encodings
people are inventing these days.

		bob wyman


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