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## org.eclipse.amp.axf.core
Interface IObservationProvider

All Known Subinterfaces:
  IModel

All Known Implementing Classes:
  ScapeWrapperModel

    public interface IObservationProvider

A model object capable of providing complete independent life-cycle information and change reporting. During the course of its existence as an instantiation within a computational context (i.e. a given vm or distributed system), a model may only transition through the following changes in state:

     [Object creation] -> Created
     [Object creation] -> Ending, Ended (Typically, a failure creating model)
     Stopped -> Created
     Created -> Initialized, Stopped (need not transition through active or initialized)
     Initialized -> Started, Stopped (need not transition through active)
     Started -> Active, Stopped (need not transition through active)
     Active -> Stopped
     Stopped -> Initialized
     Stopped -> Created (optional? TBD)
     Stopped -> Ending
     Ending -> Ended

Of course, a model may treat any transition as trivially as desired and so may effectively transition through multiple state changes at once (though any models also implementing ILifecycle notifier must report each of these transitions individually). A given model then should not undergo the following transition at any point:

     Ended -> {Any other state}

A model can be in multiple states at once; in fact, given the transition rules above, if a model is in one of the following states then they must also be in one of the first set of states and cannot be in any of the following set of states.

     Initialized: {Created} {Stopped, Ended, Ending}
     Started: {Created, Initialized} {Stopped, Ended, Ending}
     Active: {Created, Initialized, Started} {Stopped, Ending, Ended}
     Stopped: {Created, Ending, Ended} {Active, Started}
     Ending: {Stopped} {Active, Started}
     Ended: {Created, Initialized} {Active, Started, Ending}

See individual states for more details.

Method Summary
`boolean` | `isActive()` Is the model currently active? Any model that has been started and has not stopped is considered active, even if the model is not actively executing (using CPU cycles or advancing from one state to another.)
`boolean` | `isCreated()` Has the model been created? Should return true if observable start time components have been created.
`boolean` | `isEnded()` Has model has ended? In general, a model that has ended can never be (re) started.
`boolean` | `isEnding()` Is the model currently in the process of ending itself? This state gives views a chance to get any final state while the model is still guaranteed to be available and consistent.
`boolean` | `isInitialized()` Has the model been initialized? Should return true if all time 0 components have been created and initialized.
`boolean` | `isStarted()` Has the model been started?
`boolean` | `isStopped()` Has the model been stopped? When a model has been stopped, it cannot return to active state without being (re) started.

Method Detail

### isCreated

    boolean isCreated()

  Has the model been created? Should return true if observable start time components have been created. It is up to implementation to define semantics of when a model is created vs. when it is initialized, but the following guidelines are recommended to ensure good model repeatability and performance. To be considered created, a model needs:

       1. Internally consistent state.
       2. Consistent start state across invocations with same input sets.
       3. Consistent (and ideally, useful and complete!) external state through all supplied providers.
       4. Accurately updated life cycle state.
       5. In general, all basic component structure constructed.

  A good way to think of this state is as having all scaffolding in place. As outlined in #isInitialized, there should be no calls to random functions before the model has passed through this state. It is up to the implementation to decide (and seems generally reasonable) whether to allow a model to be re-created, and clients should generally handle this situation gracefully.

  Returns:
    true, if the model is created
  See Also:
    `for important issue re: randomness and repeatability`

### isInitialized

    boolean isInitialized()

  Has the model been initialized? Should return true if all time 0 components have been created and initialized. It is up to implementation to define semantics of when a model is created vs. when it is initialized, but the following guidelines are recommended to ensure good model repeatability and performance. To be considered initialized, a model ideally has:

       1. All model components necessary for running the model forward have been created and had initial state set.
       2. Model state should be recoverable to initialized state after stopping and (re) starting without passing through created state.
       3. For a given set of inputs, under (2) this state should be be consistent, regardless of whether the model has been newly created or repeatedly returned to initialized state.

  Note a very important consequence of the above guidelines for initialized state. No random decisions affecting model state should occur before the model leaves the start state and enters the initializing state as those decisions would make it impossible to consistently re-enter the same state.

  Returns:
    true, if the model is fully initialized

### isStopped

    boolean isStopped()

  Has the model been stopped? When a model has been stopped, it cannot return to active state without being (re) started.

  Returns:
    the period

### isStarted

    boolean isStarted()

  Has the model been started?

  Returns:
    the period

### isActive

    boolean isActive()

  Is the model currently active? Any model that has been started and has not stopped is considered active, even if the model is not actively executing (using CPU cycles or advancing from one state to another.)

  Returns:
    the period

### isEnding

    boolean isEnding()

  Is the model currently in the process of ending itself? This state gives views a chance to get any final state while the model is still guaranteed to be available and consistent.

  Returns:
    the period

### isEnded

    boolean isEnded()

  Has model has ended? In general, a model that has ended can never be (re) started. It is up to implementations to define whether model state is consistent and stable following the transition to ended state.

  Returns:
    the period

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