protobuffs

message Person {
  required string name = 1;
  required int32 id = 2;
  optional string email = 3;

  message PhoneNumber {
    required string number = 1;
    message PhoneType {
        optional int32 mobile = 1;
        optional int32 home = 2;
        optional int32 work = 3;
    }
    optional PhoneType type = 2;
  }

  repeated PhoneNumber phone = 4;
}