Which devices require registration and which one are 'dependent'?

[Whathecode]

While continuing the implementation of DeploymentService, some questions arose in regards to the registration of devices, and when devices are considered 'dependent' on one another.

Dependent devices The original reason why it was expected that some devices require registration prior to being able to retrieve the PrimaryDeviceDeployment of another device was because they might need to communicate and information needs to be exchanged in order to establish that communication. However, we also envisioned that the back-end may decide to only support server/client communication in between multiple primary devices; that is, the individual primary devices do not depend on one another, but all depend on the server as the middleman to communicate with one another. Since this would be the default fallback mechanisms, this is the first form of communication we intend to implement. In case of such a deployment, primary devices do not depend on one another. To contrast, the current implementation assumes they always do, even if no form of communication between them is configured in the study protocol.

• We should likely clarify what 'dependent' means. Functionally, the concept was introduced to withhold PrimaryDeviceDeployment in case the information on how to communicate with other devices was not yet available and could not yet be made part of that deployment information.

Required registration Some ambiguity in terms of what it means for a device 'requiring registration' arose. The concept was introduced to indicate the dependencies described above, and thus all top-level primary devices by default required registration. However, now the question also arises whether all devices should be registered prior to a study deployment being able to 'start'. Connected devices can be registered locally on a primary device, but it might make sense to notify the back-end of that registration so that a complete history of which physical devices were used to run a study is available.

• Do we require registration of all registrable devices on the back-end as part of configuring a deployment so that it may become 'ready' to start?
• Should we rename/redefine the concept of 'requiring registration'?

[Whathecode]

The second part 'required registration' is addressed in https://github.com/cph-cachet/carp.core-kotlin/pull/119.

All devices require registration on the back-end before a deployment can be considered 'ready' (https://github.com/cph-cachet/carp.core-kotlin/commit/eb4aa8862be1cb24c8272a6dce7c8004b96ee782). The previous requiresRegistration is now specific to individual devices, represented as remainingDevicesToRegisterBeforeDeployment in DeviceDeploymentStatus (https://github.com/cph-cachet/carp.core-kotlin/commit/b067518d733e0886ea86865541b6d197aaf8aa9a).

[Whathecode]

Another formulation I just wrote up while looking into the different definitions again:

• Dependent devices: all primary devices another primary device depends on the registration of to run the study deployment.
• All dependent devices need to be registered before the deployment for a device can be obtained (PrimaryDeviceDeployment). The intent is that a new PrimaryDeviceDeployment needs to be obtained if the dependent primary device changes its registration, since it might impact the whole 'connection' setup which is defined within.
• Not all devices need to be registered prior to retrieving PrimaryDeviceDeployment. They might be optional parts of a study (not implemented yet), or will be configured on the primary device itself.
• But, all devices need to be registered before the study deployment can start (except optional devices if we implement that later).

The current comments and variable naming in DeviceDeploymentStatus might not be in sync with this description, and it seems there is a bug as a result that a deployment for a master device cannot be obtained before registering a connected device.