def serialize_database(metamodel):
    '''
    Serialize all instances, class definitions, association definitions, and
    unique identifiers  in a *metamodel*.
    '''
    schema = serialize_schema(metamodel)
    instances = serialize_instances(metamodel)
    identifiers = serialize_unique_identifiers(metamodel)
    
    return ''.join([schema, instances, identifiers])
Serialize all instances, class definitions, association definitions, and
    unique identifiers  in a *metamodel*.