Devices in the Google Home ecosystem can be implemented using
Cloud-to-cloud, Matter, or both. Some device
types are more complex than others, and present a challenge to develop when
using the Home APIs in a way that permits smooth interfacing with other devices
in the ecosystem.

One of the challenges in implementing some of these device types is that the
devices can be composed of different combinations of traits. Not all
combinations work as well as others. Also, the Cloud-to-cloud data
model maps to the Matter data model, but not always in a
clear, one-to-one fashion. See [Data model on
Android](https://developers.home.google.com/apis/android/data-model), which discusses the data models and their
mappings in more depth.

This page contains more information the data models for specific devices map to
one another, and offers some guidance on which traits to use to implement those
device types.

## Oven

The Oven
([`OvenDevice`](https://developers.home.google.com/reference/kotlin/com/google/home/matter/standard/OvenDevice))
device type and its component traits are not as straightforward to implement
compared to other device types. There are multiple ways to implement an Oven in
Matter, but not all approaches result in seamless
interoperation with other devices or with the Google Home ecosystem.

### Trait mapping

| **Caution:** The information that follows is subject to change. In the event that it does, Oven implementations and automations based on this guidance may cease to operate as required.

Rather than implementing a Matter Oven device using the
Oven Mode and On Off clusters, we recommend using the Oven Cavity Operational
State cluster. This cluster is represented in the Home APIs by the
[`OvenCavityOperationalState`](https://developers.home.google.com/reference/kotlin/com/google/home/matter/standard/OvenCavityOperationalState)
trait, and maps to the Cloud-to-cloud
[`RunCycle`](https://developers.home.google.com/cloud-to-cloud/traits/runcycle) trait. It defines phases such as
"pre-heating", "pre-heated", and "cooling down".

| Home APIs | Cloud-to-cloud |
|:---:|:---:|
| [`OvenCavityOperationalState`](https://developers.home.google.com/reference/kotlin/com/google/home/matter/standard/OvenCavityOperationalState) | [`RunCycle`](https://developers.home.google.com/cloud-to-cloud/traits/runcycle) |

There are limitations to the Cloud-to-cloud Oven data model. The
Cloud-to-cloud Oven data model only allows for a single chamber,
with a single `RunCycle`. In contrast, Matter models a
multi-chamber Oven as a device endpoint with an Oven Cavity Operational State
cluster for each chamber.

For some Oven devices, it may be appropriate for the phase list to change at
runtime. For example, Ovens that support preheating could have different
entries in the phase list during the preheating phase than during the heating or
cooldown phases.

### Recommended implementation

As discussed in the previous section, a Matter Oven
implementation should implement the Oven Cavity Operational State cluster, which
is modeled in the Home APIs as the
[`OvenCavityOperationalState`](https://developers.home.google.com/reference/kotlin/com/google/home/matter/standard/OvenCavityOperationalState)
trait.

For best results, ensure that your Cloud-to-cloud Oven device
implements the [`RunCycle`](https://developers.home.google.com/cloud-to-cloud/traits/runcycle) trait and publish
the current state by setting the `currentRunCycle` attribute. This attribute is
observable by the Home APIs through the
[`OvenCavityOperationalState.phaseList`](https://developers.home.google.com/reference/kotlin/com/google/home/matter/standard/OvenCavityOperationalState.Attribute#phaseList)
and
[`OvenCavityOperationalState.currentPhase`](https://developers.home.google.com/reference/kotlin/com/google/home/matter/standard/OvenCavityOperationalStateTrait.Attributes#currentPhase())
attributes.

The Oven device should also publish a run cycle device notification by updating
the `priority`, `status`, and `currentCycleRemainingTime` attributes of
`RunCycle`. The following example results in an
[`OperationalState.OperationCompletion`](https://developers.home.google.com/reference/kotlin/com/google/home/matter/standard/OperationalStateTrait.OperationCompletion) event being sent, and can be used
to indicate that the oven has transitioned from the 'pre-heating' cycle to the
'pre-heated' cycle:  

    {
      "currentRunCycle": [
        {
          "currentCycle": "pre-heating",
          "nextCycle": "pre-heated",
          "lang": "en"
        }
      ],
      "currentTotalRemainingTime": 1200,
      "currentCycleRemainingTime": 300
    }

| **Important:** The event publication should occur simultaneously with the actual device state change, or *immediately after* . **Don't send the event before the state change**.

### Use an Oven in an automation

When building an automation for an Oven implemented using the
Oven Cavity Operational State cluster, reference the `currentPhase` attribute to
know what cycle the oven is in:  

       sequential {
        val starterNode =
          starter<_>(oven, OvenDevice, OvenCavityOperationalState /* Or OperationalState */)
        condition {
          expression = starterNode.phaseList[operationalState.currentPhase.toUInt()] equals "pre-heated"
        }
        action(speaker, SpeakerDevice) {
        command(AssistantBroadcast.broadcast("Oven Cycle Complete"))
      }
      // Additional actions here as needed
    }

For a complete example, see [Blink the lights and announce when the oven reaches
the chosen temperature](https://developers.home.google.com/apis/android/automation/examples#blink-lights).