public new FeatureDatasetDefinition GetDefinition()

{
  // Must be called within QueuedTask.Run
  void IterateDatasetsFromAFeatureDataset(Geodatabase geodatabase, string featureDatasetName = "City", string featureClassInFeatureDataset = "Buildings")
  {
    // Open a feature dataset
    using (FeatureDataset cityFeatureDataset = geodatabase.OpenDataset<FeatureDataset>(featureDatasetName))
    {
      // Get a feature class definition from a feature dataset
      FeatureClassDefinition buildingsFeatureClassDefinition = cityFeatureDataset.GetDefinition<FeatureClassDefinition>(featureClassInFeatureDataset);

      // Iterate dataset definition
      IReadOnlyList<FeatureClassDefinition> cityFeatureClassDefinitions = cityFeatureDataset.GetDefinitions<FeatureClassDefinition>();
      foreach (FeatureClassDefinition cityFeatureClassDefinition in cityFeatureClassDefinitions)
      {
        // Use feature class definition ...
      }
    }
  }
}