Meaning of IDL

[Jonathan S. Shapiro]

Since this is a separate thread, I'm sending a second note with a
different subject.

We were surprised in CapIDL that the syntactic migration was small
(aside: some of the OMG people have been talking with us about their
next generation IDL). We did run into several areas where the two
designs are solving different problems.

1. CORBA is designed to describe interfaces on servers, and there is an
implicit assumption that the protocol has two big steps: (a) find the
server, (b) speak on an interface.  In a capability system, you already
have the interface descriptor, so step (a) is unnecessary. It also
presents a complex set of security issues.

2. The CORBA model is client/server. The CapIDL model (and the
capability model more generally) is client/interface. A client may hold
multiple capabilities implementing distinct interfaces. It may turn out
that these are all implemented by the same server process, but the
client will not know this unless the server agrees to disclose it.

This has minimal syntactic impact, but it is a significant conceptual
deviation from CORBA. I'm curious whether a parallel deviation has
occurred in HurdLand.