Variable and device states

[clavay]

I want to implement a way to define, use and access variable and device error/state.

This could lead to:

• know if there is an error while:
  • connecting to the device,
  • reading a value,
  • writing a value,
• display the state:
  • last state and as time series in the user interface for defined user groups,
  • should we use:
    • the Variable model with RecordedData or another database model,
    • the VariableProperty model (need to add a way to store historical data),
• integrate status change in event management and take decision for some state like:
  • stop reading/writing after some retries,
  • delay reading/writing,
  • send message in user interface/email,
• it should be easy to manage from the admin and user interfaces (auto created, quick state access)

@trombastic: What do you think ?