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   Re: [xml-dev] ASN.1 is an XML Schema Language (How many encodings?)

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Bob Wyman wrote:
> Claude L Bullard wrote:
>>given your years of experience, why are multiple 
>>encodings ever necessary excepting the binary which 
>>I put in a class of its own?

> 	Whatever the case, I think you'll typically see much more
> *need* for variety in textual encodings rather than in the binary
> encodings. But, to answer your original question, I think that many of
> the alternative encodings are simply unnecessary. But, it turns out
> that the effort needed to support two encodings is pretty much the
> same effort needed to support any number greater than one. Thus, it
> makes sense to go the tiny extra step and provide support for any
> number while doing one's best to ensure that there are really only
> two....

Although I'm usually a sworn enemy of glib one-liner rules like "Worse 
Is Better" and so on, one I do tend to find myself supporting is the 
'Zero, One or Infinity Rule' - namely that, in designing computer 
systems, you should either provide for zero of something, one of 
something, or any number of something; any other limitation chosen is 
likely to be arbitrary and incorrect in hindsight :-)

I agree that there's little need for more than one written form and one 
inter-computer form. I prefer systems where computers between machines 
always uses the 'binary' inter-computer form, and the written form is 
only ever involved when communicating with a human - so it has no 
bearing on 'interoperability' at all.

However, as Bob says, politics will require us to support multiple 
encodings; PER was created because people complained BER was too 
verbose. And people will make new encodings just because they want to 
reinvent the wheel, or have failed to research things properly. Also, 
sometimes you need to make new encodings to deal with new unanticipated 
requirements; DER was created because some people needed a canonical 
encoding, and BER had "encoder's options" in it, and unused bits could 
contain any value the encoder liked, etc.

This learning process also PARTICULARLY applies to data compression and 
encryption, since technological advancements are always forcing new 
requirements on us there, but these might be considered to be 
lower-level issues than mapping from abstract values -> bytes; they're 
all about how one represents that resulting byte stream.

> 		bob wyman



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