What is a scene, really?

[Zeph]

This comes partly from the brainstorming about variable types.

What is a scene and what does it mean for it to be on or off?

My best understanding:

Defining a scene consists of creating a collection of commands to be sent when the scene is first turned ON.
    Setting the scene ON means sending those commands.
    Setting the scene OFF is not as clear.

A scene being in a state of "ON" just means the commands have been sent and the scene hasn't been turned OFF.

However, the devices may have received other commands so they may or may not be in the state they were commanded to go to when the scene was first invoked. So for example the scene might turn a given light on, but something else can later turn off that light while the Scene is still considered ON (or vice versa). That is, the status of a scene being on doesn't mean that all the devices are maintained in the given state, only that they once were told to go to that state.

Scenes are not mutually exclusive. So you could turn on Scene 1 and then Scene 4 and both would be considered active. Furthermore, Scene 4 could have changed the state of some of the devices commanded by Scene 1. So activating Scene 1 and then 4 might be different than 4 and then 1, if there are devices which are controlled differently in both scences.

Is this accurate? And is there any cross-controller consistent concept of what turning off a Scene does?

[hek]

A scene controller (in the z-wave world), usually just i a wall-control with multiple (on/off) buttons, Like light switches.

So turning scene 1 on simply means turning the button 1 in its on-position.

It's a pure actuator.

[Zeph]

@hek said:

A scene controller (in the z-wave world), usually just i a wall-control with multiple (on/off) buttons, Like light switches.

A Scene controller is a device which can trigger one or more pre-defined Scenes. That part is fairly simple and straightforward. The question in this thread is "What is this 'Scene' that it can trigger?".

So turning scene 1 on simply means turning the button 1 in its on-position. It's a pure actuator.

I think that's too narrow. Many home automation systems define scenes in software, without any need for there to exist a wall mounted button device which triggers them. A scene can be triggered by time or by a threshold being met or whatever.

---

One key question about the nature of a scene is whether it's an extended command - sort of a macro that invokes other commands, or a state based system which does something continuously for as long as it's in that state?

What's the difference?

Suppose a scene includes "set living-room-lamp to 50% and set thermostat to 25 degrees". (It could also turn lamps OFF or fully ON or raise the blinds or whatever).

• If a scene is a type of command macro system, then it's a one time set of commands to send, each of which can be freely overridden by the next command (eg: set living-room-lamp 0%) - from another scene or manually sent via the UI or whatever. Once the scene is triggered (set ON), it sends the commands once and is done - no followup.

• If a scene was a reporting state system, then after sending the initial commands, it would monitor the lamp and thermostat for changes. While the devices remain in the initially commanded state the Scene would report itself as ON. As soon as either device's state was changed (eg: by another command or scene) then the Scene would report its own state as OFF because the conditions is describes are no longer true. This is the default with Vera (With Vera, you can also select that the scene will report as activated "if ANY light is turned off", which makes no sense to me)

• If a scene was a controlling state system, then it would maintain the living room lamp at 50% and the thermostat to 25 degrees until the scene was commanded to be OFF, overriding any changes from other sources.

All three concepts could be useful (tho the controling state approach would have problems if another controlling state scene set the same devices differently, so you'd need conflict resolution rules).

However, as best I understand it, the Scene concept is usually the first or second of these; either a fire and forget collection of commands to send and then do nothing, or send and then monitor the same devices and report the scene active iff all of them are still in the desired state.

Is that other people's understanding too?

And in the general cross-system case, what is the effect of turning a Scene OFF?

Suppose that before turning the scene on, the living-room-lamp was at 100%. The scene in question sets it to 50%. What is the effect of turning that Scene OFF? Should the lamp go back to 100%, remain unchanged (ie: 50% unless something else has changed it), or go to 0%?

If a scene is a command macro, turning it OFF doesn't make much sense. If it was a controlling state system, then turning it off would mean ceasing to continually control the devices and letting other commands and macros change them. If it was a reporting state system it would mean ceasing to monitor the device states (if it had not already turned itself off after detecting some change).