[
Lists Home |
Date Index |
Thread Index
]
Robin Berjon wrote:
> Alessandro Triglia wrote:
>
>> Amelia A. Lewis wrote:
>>
>>> We believe in unicode and concrete syntax.
>>
>>
>> Good. So you don't believe in schemas. That's fine. Just use XML 1.0.
>
>
> I don't think that that happens to be what Amy said (apologies if I
> presume wrong). The fact is that at this point in time any schema
> language for XML defines one single concrete syntax. And a fair part of
> what the ASN.1 people do not seem to understand is that the XML folks
> see that as a *good* thing.
>
> 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!
Nah, just BER. BER is the Basic encoding after all - any general ASN.1
tool will handle BER; the others are more optional.
This really comes down to application profiles - IIRC, in the original
use of ASN.1 as Layer 6 of the OSI stack, everyone HAD to support BER
and could optionally support others.
Although when people define a data structure in ASN.1 and then say "It
must be encoded in PER", they then choose not to require their parsers
to support BER - that's up to them, of course.
But in any situation where more than one transfer syntax is allowed, BER
should be one of them...
Also, it's not as much of a problem as you imagine having all those
different sets of encoding rules - since the code for each of them
really only needs to be written once as part of the toolkit; from there
on up, everything else can be syntax-agnostic.
XML is even worse than ASN.1 in this respect, of course; XML is based
upon "text", and there are myriad ways of representing this.
An XML parser needs to understand (IIRC) US-ASCII, UTF-8, and UTF-16 or
something like that, so it could well barf on something written in
EBCDIC. So a truly universal XML parser really ought to support every
encoding listed under:
http://www.iana.org/assignments/character-sets
XML is *not* a concrete syntax in terms of actual bytes on the wire, by
any stretch of the imagination; it's concrete in terms of *characters*,
but those "characters" are still abstract things in terms of bits on the
wire.
Anybody who is looking for a single concrete syntax ought to leave XML
alone right now and try XDR (RFC1014; http://www.faqs.org/rfcs/rfc1014.html)
ABS
|
