A: Below we see a case where we set the row archival visibility parameter to "all"
thereby allowing us to see all of the rows that have been logically deleted:
alter session set row archival visibility = all;
We can then turn-on row invisibility back on by changing row archival visibility = "active":
alter session set row archival visibility = all;
B: To use ora_archive_state as an alternative to deleting rows, you need the following settings and parameters:
1.Create the table with the row archival clause
create table mytab (col1 number, col2 char(200)) row archival;
2.Now that the table is marked as row archival, you have two methods for removing rows, a permanent solution with the standard delete DML, plus the new syntax where you set ora_archive_state to a non-zero value:
update mytab set ora_archive_state=2 where col2='FRED';
3.To make "invisible rows" visible again, you simply set the rows ora_archive_state to zero:
update mytab set ora_archive_state=0 where col2='FRED';
Note:
* Starting in Oracle 12c, Oracle provides a new feature that allow you to "logically delete" a row in a table without physically removing the row. This effectively makes deleted rows "invisible" to all SQL and DML, but they can be revealed at any time, providing a sort of "instant" rollback method.
To use ora_archive_state as an alternative to deleting rows.

Explanation/Reference:
Explanation:
D: The database internally uses standard file system interfaces to create and delete files as needed for the following database structures:
Tablespaces
Redo log files
Control files
Archived logs
Block change tracking files
Flashback logs
RMAN backups
Note:
* Using Oracle-managed files simplifies the administration of an Oracle Database. Oracle-managed files eliminate the need for you, the DBA, to directly manage the operating system files that make up an Oracle Database. With Oracle-managed files, you specify file system directories in which the database automatically creates, names, and manages files at the database object level. For example, you need only specify that you want to create a tablespace; you do not need to specify the name and path of the tablespace's datafile with the DATAFILE clause.
http://www.oracle-base.com/articles/9i/oracle-managed-files.php
http://docs.oracle.com/cd/B10500_01/server.920/a96521/omf.htm
References:

Explanation/Reference:
Explanation:
Interesting behavior in 12.1.0.1 DB of creating an undo tablespace in a PDB. With the new Multitenant architecture the undo tablespace resides at the CDB level and PDBs all share the same UNDO tablespace.
When the current container is a PDB, an attempt to create an undo tablespace fails without returning an error.

Explanation/Reference: