Re: Targetted events

[mcs101main@xxxxxxx]

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I want a setup such that I turn the stairway lamps on and then 5
minutes later I turn them off unless something else has turned them on
inbetween. Now I can't easily tell if something else turned them on if
they didn't issue an event message to tell me this (as they didn't
change state

snip above

If the application needs to know if some other application turned on a
light then it needs to monitor the traffic to see if this light was turned
on.  This is because the .event should only be generated on an event
change.  It could also be the case that the schema defines a .acknowledge
where each command action results in the .acknowledge and is independent of
the prior state.  This .acknowledge would then be able to handle the
situation where the light was turned on by some other mechanism other than
a message (e.g. manual control of the switch).  If the manual control
situation is not a concern then the .acknowledge is really redundant with
the inital message that commands the light to be turned on, save a
communication error which could just as easily occurred on the .acknowledge
as the initial command message.


-------------- Original message from Stuart Booth : -------------- On Sat,
19 Jun 2004 12:10:19 +0000, mcs101main@xxxxxxx wrote:

>It seems like the Q1 & q2 questions posed are out of some centext
that I have not been tracking, but I'll throw in my view.

It's fairly general in that it can apply to a change of state on a
Transport e.g. Play on some MP3 receiver perhaps, or ON to some kind
of switch. Or in my case a change to a variable in the RR, or even to
the enablement state of its IR detector.

Kevin asked elsewhere what should occur if an event message should be
sent if a change of state was requested, even if the device was
already in that state. Should it send a .Info message or a .Event
message.

I've just arrived at a similar thought whilst tidying up the RR
Connector and want to do The Right Thing.

>If the content of the message means something different to different
nodes then the message should have a target address.
> If the content of the message means the same to all nodes then no
target address is used.

I'd agree with that. A query is a response to a particular node. A
command that (maybe) changes state and generates an event is of
interest to all, regardless of a response target.

>A node that supports events has a list of events that it will generate
based upon some criteria.
>If the receipt of a message does not trigger one of these criteria then
an event message should not be sent.
>
>The content of an event messages needs to adhere to the
optional/required key specification of the schema,
>but in general I would think that only the key that has changed would
be reported as an event.
>The status of all keys would be reported as an Info message.

So send a .Event message detailing exactly what has changed, and a
.Info as a compound statement of all that is known.

This might result in an empty message (but presumably not invalid in
the context of a .Event section of the schema) if nothing actually
changes, but it does provide confirmation that the original request
was at least acted upon. However the empty message is redundant.

>If the original sending node is expecting an event change and the
message that it sent did not result in one
>then we have situation of a design fault or a communication fault.  If
it is important to the sending node
>that he receives a message acknowledge then he needs to send a query
message to confirm.

Kevin previously wrote some words with a good description of this
problem. I hope he won't mind me copying a chunk from it!

66
I want a setup such that I turn the stairway lamps on and then 5
minutes later I turn them off unless something else has turned them on
inbetween. Now I can't easily tell if something else turned them on if
they didn't issue an event message to tell me this (as they didn't
change state :-(
99

S
--
Stuart Booth <stuart@xxxxxxx>
xAPFramework.NET - a xAP software development framework for .NET

http://www.xapautomation.org/ 
     http://www.xapframework.net/