public sealed class FeatureDatasetDefinition : Definition, System.IDisposable  

public async Task ObtainingDefinitionFromGeodatabase()
{
    await ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
    {
        using (Geodatabase geodatabase = new Geodatabase(new DatabaseConnectionFile(new Uri("path\\to\\sde\\file\\sdefile.sde"))))
        {
            // Remember that for Enterprise databases you have to qualify your dataset names with the DatabaseName and UserName.
            TableDefinition enterpriseTableDefinition = geodatabase.GetDefinition<TableDefinition>("LocalGovernment.GDB.CitizenContactInfo");

            // It does not matter if the dataset is within a FeatureDataset or not.
            FeatureClassDefinition featureClassDefinition = geodatabase.GetDefinition<FeatureClassDefinition>("LocalGovernment.GDB.FireStation");

            // GetDefinition For a RelationshipClass.
            RelationshipClassDefinition relationshipClassDefinition = geodatabase.GetDefinition<RelationshipClassDefinition>("LocalGovernment.GDB.AddressPointHasSiteAddresses");

            // GetDefinition For a FeatureDataset.
            FeatureDatasetDefinition featureDatasetDefinition = geodatabase.GetDefinition<FeatureDatasetDefinition>("LocalGovernment.GDB.Address");
        }
    });
}

public async Task ObtainingDefinitionsFromGeodatabase()
{
    await ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
    {
        using (Geodatabase geodatabase = new Geodatabase(new DatabaseConnectionFile(new Uri("path\\to\\sde\\file\\sdefile.sde"))))
        {
            IReadOnlyList<FeatureClassDefinition> enterpriseDefinitions = geodatabase.GetDefinitions<FeatureClassDefinition>();
            IEnumerable<Definition> featureClassesHavingGlobalID = enterpriseDefinitions.Where(definition => definition.HasGlobalID());

            IReadOnlyList<FeatureDatasetDefinition> featureDatasetDefinitions = geodatabase.GetDefinitions<FeatureDatasetDefinition>();
            bool electionRelatedFeatureDatasets = featureDatasetDefinitions.Any(definition => definition.GetName().Contains("Election"));

            IReadOnlyList<AttributedRelationshipClassDefinition> attributedRelationshipClassDefinitions = geodatabase.GetDefinitions<AttributedRelationshipClassDefinition>();

            IReadOnlyList<RelationshipClassDefinition> relationshipClassDefinitions = geodatabase.GetDefinitions<RelationshipClassDefinition>();
        }
    });
}

public void DeleteFeatureDatasetSnippet(Geodatabase geodatabase)
{
    // Deleting a FeatureDataset named as 'Parcel_Information'

    FeatureDatasetDefinition featureDatasetDefinition = geodatabase.GetDefinition<FeatureDatasetDefinition>("Parcel_Information");
    FeatureDatasetDescription featureDatasetDescription =
      new FeatureDatasetDescription(featureDatasetDefinition);

    SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

    // Delete an existing feature dataset named as 'Parcel_Information'
    schemaBuilder.Delete(featureDatasetDescription);
    schemaBuilder.Build();
}