Logic: Distributed or Centralised?

["Andy Laurence" <andy@xxxxxxxxxxxxxxxxxx>]

I'm trying to get a handle on how the logic works with the xap-enabled
devices/software available today.  I understand that some devices will
send messages, and other devices will action events based on them.
What I've not worked out yet is where the logic is applied.  Does the
input device send a control message?  Does the control device listen
for status messages from a certain device?  Do I need a piece of
hard/software that listens for status messages and outputs control
messages?

Using a scenario, if I had a xap-enabled NetIOM, could I configure it
to send status messages when an input is triggered, and to toggle a
relay at the same time?  Would I require any external hardware for
this?  If I do, I've been offered a Sharp Zaurus, which would be an
excellent piece of hardware for running HA applications.  It's low
power, has a built-in user interface, and runs Linux, so applications
are easy to port to it.

Cheers,
Andy