unknown exceptions

[Sai-Lai Lo]

> This can happen because of a versions mismatch between the
> two as well as because exceptions have to walk through a chain of nested
> implementations where the first one doesn't own any static info (IDL) about
> subsystems logically far away.

When a client invokes on an object and receives a user exception that is
not defined in the operation signature, this is an interface violation and
it seems to me it should be treated as a system exception.
(UnknownUserException is not a system exception and hence cannot be used.)
If the client is part of a nested call chain, it cannot let this unknown
user exception to propagate through its own interface to its caller as this
would violate its own interface specification as well. May be the system
exception should be augumented to carry additional data.

On the issue of interface version mismatch, I think this needs to be
addressed on a wider scale and not just the handling of exceptions. Other
parts of an operation signature may be different as well. I'm not sure we
can solve the problem with any ad hoc solution.

Regards,

Sai-Lai

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