Active Data Guard :  While the standby is open read-only  on the same time the physical standby database can be  in recovery mode  is called  ACTIVE  DATA GUARD.

Advantage

This allows you to use this standby as a real-time reporting database or even to backup the primary data, also as a result it does not have any impact on RTO or RPO.

The following operations are disallowed

•          Any Data Manipulation Language (DML) except for select statements
•            Any Data Definition Language (DDL)
•            Access of local sequences
•            DMLs on local temporary tables

·    

Note :-However, this benefit is offset to a certain extent by the fact that Active Data Guard is available on Enterprise Edition only and is cost option which must be licensed on both the primary and standby database.

Steps To create Active DATA Guard .

    1) Check the status of the Primary database and  Physical standby database and the latest sequence generated in the primary database.

Primary

select status,instance_name,database_role from v$instance,v$database;

STATUS       INSTANCE_NAME    DATABASE_ROLE

------------ ---------------- ----------------

OPEN         ORCL           PRIMARY

 select max(sequence#) from v$archived_log;

MAX(SEQUENCE#)

--------------

3333

Standby

select status,instance_name,database_role from v$database,v$instance;

STATUS   INSTANCE_NAME DATABASE_ROLE

-------- ------------- ---------------------

MOUNTED  ORCL_STBY         PHYSICAL STANDBY

SQL> select max(sequence#) from v$archived_log where applied='YES';

MAX(SEQUENCE#)

--------------

3333

)     Check if the Managed Recovery Process (MRP) is active on the physcial standby database.

select process,status,sequence# from v$managed_standby;

2)     Cancel the MRP on the physical standby database and open the standby database  in            READ-ONLY mode

alter database recover managed standby database cancel;

alter database open read only;

select status,instance_name,database_role,open_mode from v$database,v$instance;

STATUS INSTANCE_NAME  DATABASE_ROLE    OPEN_MODE

------ -------------- ---------------- ---------------

OPEN   ORCL_STBY            PHYSICAL STANDBY READ ONLY

   3)    start the MRP on the physical standby database.

alter database recover managed standby database disconnectfrom session;

                                                                                                                                 

4)       Database is now Active Data Guard

 SELECT database_role, open_mode FROM v$database;

DATABASE_ROLE    OPEN_MODE

---------------- --------------------

PHYSICAL STANDBY READ ONLY WITH APPLY

How To Set Up Physical Standby Database You Can Check Here 

                     http://adminoracle10g.blogspot.in/2014/08/physical-standby-database-implementation.html