12 Using Oracle Flashback Technology

Application Development Features

In application development, you can use these flashback features to report historical data or undo erroneous changes. (You can also use these features interactively as a database user or administrator.)

Oracle Flashback Query

Use this feature to retrieve data for an earlier time that you specify with the AS OF clause of the SELECT statement. For more information, see "Using Oracle Flashback Query (SELECT AS OF)".

Oracle Flashback Version Query

Use this feature to retrieve metadata and historical data for a specific time interval (for example, to view all the rows of a table that ever existed during a given time interval). Metadata for each row version includes start and end time, type of change operation, and identity of the transaction that created the row version. To create an Oracle Flashback Version Query, use the VERSIONS BETWEEN clause of the SELECT statement. For more information, see "Using Oracle Flashback Version Query".

Oracle Flashback Transaction Query

Use this feature to retrieve metadata and historical data for a given transaction or for all transactions in a given time interval. To perform an Oracle Flashback Transaction Query, select from the static data dictionary view FLASHBACK_TRANSACTION_QUERY. For more information, see "Using Oracle Flashback Transaction Query".

Typically, you use Oracle Flashback Transaction Query with an Oracle Flashback Version Query that provides the transaction IDs for the rows of interest (see "Using Oracle Flashback Transaction Query with Oracle Flashback Version Query").

DBMS_FLASHBACK Package

Use this feature to set the internal Oracle Database clock to an earlier time so that you can examine data that was current at that time, or to roll back a transaction and its dependent transactions while the database remains online (see Flashback Transaction). For more information, see "Using DBMS_FLASHBACK Package".

Flashback Transaction

Use Flashback Transaction to roll back a transaction and its dependent transactions while the database remains online. This recovery operation uses undo data to create and run the corresponding compensating transactions that return the affected data to its original state. (Flashback Transaction is part of DBMS_FLASHBACK package.) For more information, see "Using DBMS_FLASHBACK Package".

Flashback Data Archive (Oracle Total Recall)

Use Flashback Data Archive to automatically track and archive both regular queries and Oracle Flashback Query, ensuring SQL-level access to the versions of database objects without getting a snapshot-too-old error. For more information, see "Using Flashback Data Archive (Oracle Total Recall)".

Database Administration Features

These flashback features are primarily for data recovery. Typically, you use these features only as a database administrator.

This chapter focuses on the "Application Development Features". For more information about the database administration features, see Oracle Database Administrator's Guide and the Oracle Database Backup and Recovery User's Guide.

Oracle Flashback Table

Use this feature to restore a table to its state at a previous point in time. You can restore a table while the database is on line, undoing changes to only the specified table.

Oracle Flashback Drop

Use this feature to recover a dropped table. This feature reverses the effects of a DROP TABLE statement.

Oracle Flashback Database

Use this feature to quickly return the database to an earlier point in time, by undoing all of the changes that have taken place since then. This is fast, because you do not have to restore database backups.

Configuring Your Database for Automatic Undo Management

To configure your database for Automatic Undo Management (AUM), you or your database administrator must:

• Create an undo tablespace with enough space to keep the required data for flashback operations.

  The more often users update the data, the more space is required. The database administrator usually calculates the space requirement.

• Enable AUM, as explained in Oracle Database Administrator's Guide. Set these database initialization parameters:

  • UNDO_MANAGEMENT

  • UNDO_TABLESPACE

  • UNDO_RETENTION

  For a fixed-size undo tablespace, Oracle Database automatically tunes the system to give the undo tablespace the best possible undo retention.

  For an automatically extensible undo tablespace, Oracle Database retains undo data longer than the longest query duration and the low threshold of undo retention specified by the UNDO_RETENTION parameter.

  Note:

  You can query V$UNDOSTAT.TUNED_UNDORETENTION to determine the amount of time for which undo is retained for the current undo tablespace. For more information about V$UNDOSTAT, see Oracle Database Reference.

  Setting UNDO_RETENTION does not guarantee that unexpired undo data is not discarded. If the system needs more space, Oracle Database can overwrite unexpired undo with more recently generated undo data.

• Specify the RETENTION GUARANTEE clause for the undo tablespace to ensure that unexpired undo data is not discarded.

Configuring Your Database for Oracle Flashback Transaction Query

To configure your database for the Oracle Flashback Transaction Query feature, you or your database administrator must:

• Ensure that Oracle Database is running with version 10.0 compatibility.

• Enable supplemental logging:

  ALTER DATABASE ADD SUPPLEMENTAL LOG DATA;
  

Configuring Your Database for Flashback Transaction

To configure your database for the Flashback Transaction feature, you or your database administrator must:

• With the database mounted but not open, enable ARCHIVELOG:

  ALTER DATABASE ARCHIVELOG;
  

• Open at least one archive log:

  ALTER SYSTEM ARCHIVE LOG CURRENT;
  

• If not done, enable minimal and primary key supplemental logging:

  ALTER DATABASE ADD SUPPLEMENTAL LOG DATA;
  ALTER DATABASE ADD SUPPLEMENTAL LOG DATA (PRIMARY KEY) COLUMNS;
  

• If you want to track foreign key dependencies, enable foreign key supplemental logging:

  ALTER DATABASE ADD SUPPLEMENTAL LOG DATA (FOREIGN KEY) COLUMNS;
  

Enabling Oracle Flashback Operations on Specific LOB Columns

To enable flashback operations on specific LOB columns of a table, use the ALTER TABLE statement with the RETENTION option.

Because undo data for LOB columns can be voluminous, you must define which LOB columns to use with flashback operations.

Granting Necessary Privileges

You or your database administrator must grant privileges to users, roles, or applications that must use these flashback features. For information about the GRANT statement, see Oracle Database SQL Language Reference.

For Oracle Flashback Query and Oracle Flashback Version Query

To allow access to specific objects during queries, grant FLASHBACK and SELECT privileges on those objects.

To allow queries on all tables, grant the FLASHBACK ANY TABLE privilege.

For Oracle Flashback Transaction Query

Grant the SELECT ANY TRANSACTION privilege.

To allow execution of undo SQL code retrieved by an Oracle Flashback Transaction Query, grant SELECT, UPDATE, DELETE, and INSERT privileges for specific tables.

For DBMS_FLASHBACK Package

To allow access to the features in the DBMS_FLASHBACK package, grant the EXECUTE privilege on DBMS_FLASHBACK.

For Flashback Data Archive (Oracle Total Recall)

To allow a specific user to enable Flashback Data Archive on tables, using a specific Flashback Data Archive, grant the FLASHBACK ARCHIVE object privilege on that Flashback Data Archive to that user. To grant the FLASHBACK ARCHIVE object privilege, you must either be logged on as SYSDBA or have FLASHBACK ARCHIVE ADMINISTER system privilege.

To allow execution of these statements, grant the FLASHBACK ARCHIVE ADMINISTER system privilege:

• CREATE FLASHBACK ARCHIVE

• ALTER FLASHBACK ARCHIVE

• DROP FLASHBACK ARCHIVE

To grant the FLASHBACK ARCHIVE ADMINISTER system privilege, you must be logged on as SYSDBA.

To create a default Flashback Data Archive, using either the CREATE FLASHBACK ARCHIVE or ALTER FLASHBACK ARCHIVE statement, you must be logged on as SYSDBA.

To disable Flashback Data Archive for a table that has been enabled for Flashback Data Archive, you must either be logged on as SYSDBA or have the FLASHBACK ARCHIVE ADMINISTER system privilege.

Example of Examining and Restoring Past Data

Suppose that you discover at 12:30 PM that the row for employee Chung was deleted from the employees table, and you know that at 9:30AM the data for Chung was correctly stored in the database. You can use Oracle Flashback Query to examine the contents of the table at 9:30 AM to find out what data was lost. If appropriate, you can restore the lost data.

Example 12-1 retrieves the state of the record for Chung at 9:30AM, April 4, 2004:

SELECT * FROM employees
AS OF TIMESTAMP
TO_TIMESTAMP('2004-04-04 09:30:00', 'YYYY-MM-DD HH:MI:SS')
WHERE last_name = 'Chung';

Example 12-2 restores Chung's information to the employees table:

INSERT INTO employees (
  SELECT * FROM employees
  AS OF TIMESTAMP
  TO_TIMESTAMP('2004-04-04 09:30:00', 'YYYY-MM-DD HH:MI:SS')
  WHERE last_name = 'Chung'
);

Guidelines for Oracle Flashback Query

• You can specify or omit the AS OF clause for each table and specify different times for different tables.

  Note:

  If a table is a Flashback Data Archive and you specify a time for it that is earlier than its creation time, the query returns zero rows for that table, rather than causing an error. (For information about Flashback Data Archives, see "Using Flashback Data Archive (Oracle Total Recall)".)

• You can use the AS OF clause in queries to perform DDL operations (such as creating and truncating tables) or DML operations (such as inserting and deleting) in the same session as Oracle Flashback Query.

• To use the result of Oracle Flashback Query in a DDL or DML statement that affects the current state of the database, use an AS OF clause inside an INSERT or CREATE TABLE AS SELECT statement.

• If a possible 3-second error (maximum) is important to Oracle Flashback Query in your application, use an SCN instead of a time stamp. See "General Guidelines for Oracle Flashback Technology".

• You can create a view that refers to past data by using the AS OF clause in the SELECT statement that defines the view.

  If you specify a relative time by subtracting from the current time on the database host, the past time is recalculated for each query. For example:

  CREATE VIEW hour_ago AS
    SELECT * FROM employees
      AS OF TIMESTAMP (SYSTIMESTAMP - INTERVAL '60' MINUTE);
  

  SYSTIMESTAMP refers to the time zone of the database host environment.

• You can use the AS OF clause in self-joins, or in set operations such as INTERSECT and MINUS, to extract or compare data from two different times.

  You can store the results by preceding Oracle Flashback Query with a CREATE TABLE AS SELECT or INSERT INTO TABLE SELECT statement. For example, this query reinserts into table employees the rows that existed an hour ago:

  INSERT INTO employees
      (SELECT * FROM employees
       AS OF TIMESTAMP (SYSTIMESTAMP - INTERVAL '60' MINUTE)
      )
      MINUS SELECT * FROM employees);
  

  SYSTIMESTAMP refers to the time zone of the database host environment.

Scenario: Packaged Subprogram Might Change Row

Your application examines a row of data and records the corresponding ORA_ROWSCN as 202553. Then, your application invokes a packaged subprogram, whose implementation details you cannot see, which might or might not change the same row (and commit the change). Later, your application must update the row only if the packaged subprogram did not change it. Make the operation conditional—update the row only if ORA_ROWSCN is still 202553, as in this equivalent interactive statement:

UPDATE employees
SET salary = salary + 100
WHERE employee_id = 200
AND ora_rowscn = 202553;

If the packaged subprogram changed the row, then ORA_ROWSCN is no longer 9371092, and the update fails.

Your application queries again to obtain the new row data and ORA_ROWSCN. Suppose that the ORA_ROWSCN is now 415639. The application tries the conditional update again, using the new ORA_ROWSCN. This time, the update succeeds, and it is committed. An interactive equivalent is:

UPDATE employees
SET salary = salary + 100
WHERE employee_id = 7788
AND ora_rowscn = 415639;

ORA_ROWSCN and Tables with Virtual Private Database (VPD)

When a VPD policy is added to a table, it is no longer possible to select the ORA_ROWSCN pseudocolumn. However, because ORA_ROWSCN is available inside the policy function, you can:

1. Create a function that returns a row SCN, as in Example 12-3.

2. In the policy predicate function, add a predicate that stores the row SCN in the context that the function uses while processing rows. For example:

   ||' AND f_ora_rowscn('||object_name||'.ora_rowscn) = 1'
   

3. Use the function to fetch the row. For example:

   SELECT t.*, get_rowscn(t.rowid) "ORA_ROWSCN" FROM test_table t;
   

-- Create context that function uses while processing rows:
 
CREATE OR REPLACE FUNCTION f_ora_rowscn
 (rowscn IN NUMBER)
 RETURN NUMBER
AS
BEGIN
  DBMS_SESSION.SET_CONTEXT('STORE_ROWSCN','ROWSCN',rowscn);
  RETURN 1;
END;
/
 
CREATE CONTEXT store_rowscn USING f_ora_rowscn;
 
-- Create function that returns row SCN for each row:
 
CREATE OR REPLACE FUNCTION get_rowscn
  (row IN ROWID)
  RETURN VARCHAR2
AS
BEGIN 
  RETURN sys_context('STORE_ROWSCN','ROWSCN');
END;
/

Dependent Transactions

In the context of Flashback Transaction, transaction 2 can depend on transaction 1 in any of these ways:

• Write-after-write dependency

  Transaction 1 changes a row of a table, and later transaction 2 changes the same row.

• Primary key dependency

  A table has a primary key constraint on column c. In a row of the table, column c has the value v. Transaction 1 deletes that row, and later transaction 2 inserts a row into the same table, assigning the value v to column c.

• Foreign key dependency

  In table b, column b1 has a foreign key constraint on column a1 of table a. Transaction 1 changes a value in a1, and later transaction 2 changes a value in b1.

TRANSACTION_BACKOUT Parameters

The parameters of the TRANSACTION_BACKOUT procedure are:

• Number of transactions to be backed out

• List of transactions to be backed out, identified either by name or by XID

• Time hint, if you identify transactions by name

  Specify a time that is earlier than any transaction started.

• Backout option from Table 12-2

For the syntax of the TRANSACTION_BACKOUT procedure and detailed parameter descriptions, see Oracle Database PL/SQL Packages and Types Reference.

TRANSACTION_BACKOUT analyzes the transactional dependencies, performs DML operations, and generates reports. TRANSACTION_BACKOUT does not commit the DML operations that it performs as part of transaction backout, but it holds all the required locks on rows and tables in the right form, preventing other dependencies from entering the system. To make the transaction backout permanent, you must explicitly commit the transaction.

TRANSACTION_BACKOUT Reports

To see the reports that TRANSACTION_BACKOUT generates, query the static data dictionary views *_FLASHBACK_TXN_STATE and *_FLASHBACK_TXN_REPORT.

Creating a Flashback Data Archive

Create a Flashback Data Archive with the CREATE FLASHBACK ARCHIVE statement, specifying:

• Name of the Flashback Data Archive

• Name of the first tablespace of the Flashback Data Archive

• (Optional) Maximum amount of space that the Flashback Data Archive can use in the first tablespace

  The default is unlimited. Unless your space quota on the first tablespace is also unlimited, you must specify this value; otherwise, error ORA-55621 occurs.

• Retention time (number of days that Flashback Data Archive data for the table is guaranteed to be stored)

If you are logged on as SYSDBA, you can also specify that this is the default Flashback Data Archive for the system. If you omit this option, you can still make this Flashback Data Archive the default later (see "Specifying the Default Flashback Data Archive").

Examples

• Create a default Flashback Data Archive named fla1 that uses up to 10 G of tablespace tbs1, whose data are retained for one year:

  CREATE FLASHBACK ARCHIVE DEFAULT fla1 TABLESPACE tbs1
    QUOTA 10G RETENTION 1 YEAR;
  

• Create a Flashback Data Archive named fla2 that uses tablespace tbs2, whose data are retained for two years:

  CREATE FLASHBACK ARCHIVE fla2 TABLESPACE tbs2 RETENTION 2 YEAR;
  

For more information about the CREATE FLASHBACK ARCHIVE statement, see Oracle Database SQL Language Reference.

Altering a Flashback Data Archive

With the ALTER FLASHBACK ARCHIVE statement, you can:

• Change the retention time of a Flashback Data Archive

• Purge some or all of its data

• Add, modify, and remove tablespaces

  Note:

  Removing all tablespaces of a Flashback Data Archive causes an error.

If you are logged on as SYSDBA, you can also use the ALTER FLASHBACK ARCHIVE statement to make a specific file the default Flashback Data Archive for the system.

Examples

• Make Flashback Data Archive fla1 the default Flashback Data Archive:

  ALTER FLASHBACK ARCHIVE fla1 SET DEFAULT;
  

• To Flashback Data Archive fla1, add up to 5 G of tablespace tbs3:

  ALTER FLASHBACK ARCHIVE fla1 ADD TABLESPACE tbs3 QUOTA 5G;
  

• To Flashback Data Archive fla1, add as much of tablespace tbs4 as needed:

  ALTER FLASHBACK ARCHIVE fla1 ADD TABLESPACE tbs4;
  

• Change the maximum space that Flashback Data Archive fla1 can use in tablespace tbs3 to 20 G:

  ALTER FLASHBACK ARCHIVE fla1 MODIFY TABLESPACE tbs3 QUOTA 20G;
  

• Allow Flashback Data Archive fla1 to use as much of tablespace tbs1 as needed:

  ALTER FLASHBACK ARCHIVE fla1 MODIFY TABLESPACE tbs1;
  

• Change the retention time for Flashback Data Archive fla1 to two years:

  ALTER FLASHBACK ARCHIVE fla1 MODIFY RETENTION 2 YEAR;
  

• Remove tablespace tbs2 from Flashback Data Archive fla1:

  ALTER FLASHBACK ARCHIVE fla1 REMOVE TABLESPACE tbs2;
  

  (Tablespace tbs2 is not dropped.)

• Purge all historical data from Flashback Data Archive fla1:

  ALTER FLASHBACK ARCHIVE fla1 PURGE ALL;
  

• Purge all historical data older than one day from Flashback Data Archive fla1:

  ALTER FLASHBACK ARCHIVE fla1
    PURGE BEFORE TIMESTAMP (SYSTIMESTAMP - INTERVAL '1' DAY);
  

• Purge all historical data older than SCN 728969 from Flashback Data Archive fla1:

  ALTER FLASHBACK ARCHIVE fla1 PURGE BEFORE SCN 728969;
  

For more information about the ALTER FLASHBACK ARCHIVE statement, see Oracle Database SQL Language Reference.

Dropping a Flashback Data Archive

Drop a Flashback Data Archive with the DROP FLASHBACK ARCHIVE statement. Dropping a Flashback Data Archive deletes its historical data, but does not drop its tablespaces.

Example

Remove Flashback Data Archive fla1 and all its historical data, but not its tablespaces:

DROP FLASHBACK ARCHIVE fla1;

For more information about the DROP FLASHBACK ARCHIVE statement, see Oracle Database SQL Language Reference.

Specifying the Default Flashback Data Archive

By default, the system has no default Flashback Data Archive. If you are logged on as SYSDBA, you can specify default Flashback Data Archive in either of these ways:

• Specify the name of an existing Flashback Data Archive in the SET DEFAULT clause of the ALTER FLASHBACK ARCHIVE statement. For example:

  ALTER FLASHBACK ARCHIVE fla1 SET DEFAULT;
  

  If fla1 does not exist, an error occurs.

• Include DEFAULT in the CREATE FLASHBACK ARCHIVE statement when you create a Flashback Data Archive. For example:

  CREATE FLASHBACK ARCHIVE DEFAULT fla2 TABLESPACE tbs1
    QUOTA 10G RETENTION 1 YEAR;
  

The default Flashback Data Archive for the system is the default Flashback Data Archive for every user who does not have his or her own default Flashback Data Archive.

Enabling and Disabling Flashback Data Archive

By default, flashback archiving is disabled for any table. You can enable flashback archiving for a table if you have the FLASHBACK ARCHIVE object privilege on the Flashback Data Archive that you want to use for that table.

To enable flashback archiving for a table, include the FLASHBACK ARCHIVE clause in either the CREATE TABLE or ALTER TABLE statement. In the FLASHBACK ARCHIVE clause, you can specify the Flashback Data Archive where the historical data for the table are stored. The default is the default Flashback Data Archive for the system. If you specify a nonexistent Flashback Data Archive, an error occurs.

If you enable flashback archiving for a table, but AUM is disabled, error ORA-55614 occurs when you try to modify the table.

If a table has flashback archiving enabled, and you try to enable it again with a different Flashback Data Archive, an error occurs.

After flashback archiving is enabled for a table, you can disable it only if you either have the FLASHBACK ARCHIVE ADMINISTER system privilege or you are logged on as SYSDBA. To disable flashback archiving for a table, specify NO FLASHBACK ARCHIVE in the ALTER TABLE statement. (It is unnecessary to specify NO FLASHBACK ARCHIVE in the CREATE TABLE statement, because that is the default.)

Examples

• Create table employee and store the historical data in the default Flashback Data Archive:

  CREATE TABLE employee (EMPNO NUMBER(4) NOT NULL, ENAME VARCHAR2(10),
    JOB VARCHAR2(9), MGR NUMBER(4)) FLASHBACK ARCHIVE;
  

• Create table employee and store the historical data in the Flashback Data Archive fla1:

  CREATE TABLE employee (EMPNO NUMBER(4) NOT NULL, ENAME VARCHAR2(10),
    JOB VARCHAR2(9), MGR NUMBER(4)) FLASHBACK ARCHIVE fla1;
  

• Enable flashback archiving for the table employee and store the historical data in the default Flashback Data Archive:

  ALTER TABLE employee FLASHBACK ARCHIVE;
  

• Enable flashback archiving for the table employee and store the historical data in the Flashback Data Archive fla1:

  ALTER TABLE employee FLASHBACK ARCHIVE fla1;
  

• Disable flashback archiving for the table employee:

  ALTER TABLE employee NO FLASHBACK ARCHIVE;
  

DDL Statements on Tables Enabled for Flashback Data Archive

Flashback Data Archive supports many DDL statements, including some that alter the table definition or move data. For example:

• ALTER TABLE statement that does any of the following:

  • Adds, drops, renames, or modifies a column

  • Adds, drops, or renames a constraint

  • Drops or truncates a partition or subpartition operation

• TRUNCATE TABLE statement

• RENAME statement that renames a table

Some DDL statements cause error ORA-55610 when used on a table enabled for Flashback Data Archive. For example:

• ALTER TABLE statement that includes an UPGRADE TABLE clause, with or without an INCLUDING DATA clause

• ALTER TABLE statement that moves or exchanges a partition or subpartition operation

• DROP TABLE statement

If you must use unsupported DDL statements on a table enabled for Flashback Data Archive, use the DBMS_FLASHBACK_ARCHIVE.DISASSOCIATE_FBA procedure to disassociate the base table from its Flashback Data Archive. To reassociate the Flashback Data Archive with the base table afterward, use the DBMS_FLASHBACK_ARCHIVE.REASSOCIATE_FBA procedure.

Viewing Flashback Data Archive Data

Table 12-3 lists and briefly describes the static data dictionary views that you can query for information about Flashback Data Archive files.

Flashback Data Archive Scenarios

• Scenario: Using Flashback Data Archive to Enforce Digital Shredding

• Scenario: Using Flashback Data Archive to Access Historical Data

• Scenario: Using Flashback Data Archive to Generate Reports

• Scenario: Using Flashback Data Archive for Auditing

• Scenario: Using Flashback Data Archive to Recover Data

CREATE FLASHBACK ARCHIVE taxes_archive TABLESPACE tbs1 RETENTION 10 YEAR;

CREATE FLASHBACK ARCHIVE DEFAULT fla1 TABLESPACE tbs1
  QUOTA 10G RETENTION 5 YEAR;

ALTER TABLE inventory FLASHBACK ARCHIVE;
ALTER TABLE stock_data FLASHBACK ARCHIVE;

SELECT product_number, product_name, count FROM inventory AS OF
  TIMESTAMP TO_TIMESTAMP ('2007-01-01 00:00:00', 'YYYY-MM-DD HH24:MI:SS');

SELECT symbol, stock_price FROM stock_data AS OF
  TIMESTAMP TO_TIMESTAMP ('2007-07-23 16:00:00', 'YYYY-MM-DD HH24:MI:SS')
  WHERE symbol IN my_portfolio;

CREATE FLASHBACK ARCHIVE DEFAULT fla2 TABLESPACE tbs1
  QUOTA 20G RETENTION 5 YEAR;

ALTER TABLE investments FLASHBACK ARCHIVE;

SELECT * FROM investments AS OF
  TIMESTAMP TO_TIMESTAMP ('2006-12-31 16:00:00', 'YYYY-MM-DD HH24:MI:SS')
  WHERE name = 'LISA';

CREATE FLASHBACK ARCHIVE DEFAULT fla4 TABLESPACE tbs1
  QUOTA 100G RETENTION 10 YEAR;

ALTER TABLE Billings FLASHBACK ARCHIVE;

SELECT date_billed, amount_billed, patient_name, claim_Id,
  test_costs, diagnosis FROM Billings AS OF TIMESTAMP
  TO_TIMESTAMP('2007-05-01 00:00:00', 'YYYY-MM-DD HH24:MI:SS');

DELETE EMPLOYEE WHERE MANAGER = 'LISA JOHNSON';
INSERT INTO EMPLOYEE
  SELECT * FROM EMPLOYEE
    AS OF TIMESTAMP (SYSTIMESTAMP - INTERVAL '2' DAY)
      WHERE MANAGER = 'LISA JOHNSON';