> > We've got no diagnostics for this sort of thing because it is a
> > protocol level error rather than an SRW/U level error.
> 
> ... which is a mistake, since SRW doesn't mandate a protocol.

For protocol read transport
 
> > The SRU equivalent to a SOAP fault is a http error code so I think
> > the answer should be return a http 400 erro (Bad request)
> 
> And what about when this happens in a message sent over the SMTP
> transport?  No, it needs to be recognised at the SRW level.

It would through a SOAP fault.

Matthew