public new FeatureDatasetDefinition GetDefinition()

public 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
        }
    }
}