create or replace view v_salary_emp as
select emp_name,dept_name,salary
from emp,dept
where emp.dept_id = dept.dept_id;

select * from v_salary_emp where dept = 10;

--
-- your original tables
--
create table emp ...

create table dept ...

--
-- your shadow tables that store history of the data
--
create table emp_h ...

create table dept_h ...

--
-- your original salary view that shows current data
--
create view v_salary_emp as ...

--
-- historical view which gets a date using sys_context()
-- this view is the first step in a history retrieval strategy
-- this view would return data for emp based on the date it gets
-- essentially it rolls back your database to a point in time
--
-- note we create one such view for each table
--
create or replace view v_emp_historical as
select *
from emp_h
where [Bob Barker lookup goes here using sys_context()];

create or replace view v_dept_historical as ...

--
-- create a historical user for viewing history
-- this is the second step in a historical retrieval strategy
-- creating a way for people to indicate they are doing a historical query
-- my preference is with a new user for this specific purpose
--
create user historical_user...

--
-- log into the historical user
--

--
-- create objects for each rowsource that point to your historical views and not the tables
-- notice how we are using the synonym to not only redirect to our historical view
-- but also to rename that view to the original table name
--
create synonym historical_user.emp for data_owner.v_emp_historical;

create synonym historical_user.dept for data_owner.v_dept_historical;

--
-- here is your original salary view
-- but now it points to historical views under the covers
-- notice we can compile this view in our historical user without changing it
--
create or replace view v_salary_emp as
select emp_name,dept_name,salary
from emp,dept
where emp.dept_id = dept.dept_id;

--
-- set a date for your history point in time
--
exec my_package.set_historical_date([somedate])

--
-- execute the same code you did before
-- but now it sees the historical point in time
-- there you go...
-- exactly the same code that got current data can get historical data
--
select * from v_salary_emp where dept = 10;