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Michael Champion wrote:
> Trouble is, you can't make sense of an ASN.1 message without having the
> schema, and I mean the EXACT schema, used to generate it.
That depends what encoding you use!
PER (packed encoding) doesn't make any sense without the schema, just
like you say.
BER (basic encoding, the most popular) makes some sense: The data is
annotated with field boundaries and types, so a tool can split it into a
tree and show strings as strings and integers as integers and so on, but
without variable names.
XER (XML encoding) makes some sense: The data is annotated with field
boundaries and names, so a tool can split it into a tree and show
everything as strings, but without knowledge of types.
> That's (oops,
> smell of impending flames <grin>) the value proposition for XML in a
> nutshell, IMHO, and why it is used in all those projects Simon mentioned
> where ASN.1 is, on paper, better suited.
I doubt many people who use XML for a project really consider the
alternatives. When asked, the average XML user tends to list the reason
for using XML as:
"I can share information with other programs, with any structure I want"
...because much of the XML hype has been "WOW! Now it's possible to
COMMUNICATE BETWEEN BITS OF SOFTWARE using the Internet rather than just
using it to COMMUNICATE WITH USERS!".
Many Internet developers came straight into Web development, and have
never really seen the 'big picture'. Until XML came along, their code
1) Backend server apps written by remote, distant, clever people: SQL
servers, DNS servers, LDAP servers, etc. The thought of writing one's
own "server" and "protocol" was unthinkable.
2) Users, via HTML in their browser, which was easy.
XML's biggest contribution to the Web has been to get these developers
thinking about how easy it is to set up communications between
components, rather than really making it easier, IMHO ;-)