> I believe responding in a manner which is determined by (some form of)
> identification of the client is just as deterministic as 
> responding to a
> particular request from the client. In fact it may be a more strict
> determinism as the client will only receive what its 
> identification by the
> server allows it to be sent.

Quite the opposite - the client had no idea what to expect back as it is
entirely up to what the server thinks such a client may want back. The
client may get back some information it has no idea how to handle, and
not get back something the server could have sent back and the client
could make use of.

The other approach is that the client explicitly asks for all the
additional services it knows how to handle and then the server returns
all of those additional services (but no more) which it know how to
return (this is comparable to the options negotiation in the z39.50
init). This is why a server should not return an extraData element
unless there is a corresponding extraData element in the request.

Matthew