Re: Spec revisions...

[Patrick Lidstone]

--- In <a
href="/group/xAP_developer/post?postID=pSwAXo-y-tRQ-1-D5zPCyu0uPSOU_WyVMCbAaWVAY8YBbDnVBhBfVHdjt8Ud4BQ-BQmXei9ifp3uiiGxpILvyry0fFXb">xAP_developer@xxxxxxx</a>,
Stuart Booth <lists@s...> wrote:
> On Wed, 26 Mar 2003 09:38:24 -0000, "Patrick Lidstone"
> <patrick@l...> wrote:
>
> >At the moment, senders and receivers use schema which identify
> >functionality which is specific to the device. The idea of event
> >addressing is the introduction of -abstract- events which are not
> >tied to a specific device(s), but indicate a generic, system wide
> >change of status.
>
> Do you happen to have an example of what you mean by this?
>
> Taking your audio.mute example, I'm thinking that an untargetted
> message (one-to-many) achieves the same result.

The problem is that any receiver of a "mute" message has to
explicitly be able to identify each and every possible source for the
event.

Suppose I have a four MP3 players, a TV and a home cinema system all
of which have different target addresses and all of which might be
required to respond simultaneously to an "audio.mute".

Suppose that an "audio.mute" event can be generated by: a caller
id
box, an infra-red remote control (ie. manually), by a text to speech
announcement system (so that the announcement can be heard), and by a
doorbell interface.

Each of those individual senders has to be configured to send 6
target messages [OK, I agree that it *may* be possible to target the
MP3 players with a single message, but the basic principle holds].
And, worse, if a new device is added to the network, they have to be
reconfigured. An addiitonal minor niggle is that these messages can't
be sent truly simultaneously, so there will be fractional delays
between each device being silenced.

The same argument replies round the other way if you use source
addressing...

> A many-to-many notification sounds almost like an anonymous
broadcast.
> ie no source.

The source is still present, but is ignored. Conceptually I guess you
could think of it as an anonymous broadcast.

> >Some pieces of hardware
> >may be able to support multiple logical functions that are totally
> >unrelated (e.g. Ian B's relay control, which is also capable of
input
> >switch sensing, my rabbit board which can support two completely
> >different serial devices concurrently). The fact that these two
> >functions happen to be implemented on the same device is complete
co-
> >incidence, and they really should be independently addressed. We
> >don't currently allow for that in the spec, and I think we should.
>
> Isn't that what the subaddress was intended for?

Yes and no. It was the original intention behind subaddressing, but
it only really works for related functionality. Perhaps the relay
board is a special case, but the switches and the relays have no
direct logical or functional relationship - and it doesn't make any
sense for them to share the same core address.

Patrick