# Package org.eclipse.viatra.query.runtime.api.scope

- Interface Summary
  Interface | Description
  --- | ---
  IBaseIndex | Represents the index maintained on the model.
  IEngineContext | The context of the engine is instantiated by the scope, and provides information and services regarding the model the towards the engine.
  IIndexingErrorListener | This interface contains callbacks for various internal errors from the `base index`.
  IInstanceObserver | Listener interface for lightweight observation of changes in edges leaving from given source instance elements.
  ViatraBaseIndexChangeListener | Listener interface for change notifications from the VIATRA Base index.

- Class Summary
  Class | Description
  --- | ---
  QueryScope | Defines a scope for a VIATRA Query engine, which determines the set of model elements that query evaluation operates on.