As an illustration of how schema objects can create dependencies, the following sample script creates a table test_table and then a procedure that queries this table:

CREATE TABLE test_table ( col1 INTEGER, col2 INTEGER );

CREATE OR REPLACE PROCEDURE test_proc
AS
BEGIN
 FOR x IN ( SELECT col1, col2 FROM test_table )
 LOOP
   -- process data
   NULL;
 END LOOP;
END;
/

The following query of the status of procedure test_proc shows that it is valid:

SQL> SELECT OBJECT_NAME, STATUS FROM USER_OBJECTS WHERE OBJECT_NAME = 'TEST_PROC';
 
OBJECT_NAME STATUS
----------- -------
TEST_PROC   VALID

After adding the col3 column to test_table, the procedure is still valid because the procedure has no dependencies on this column:

SQL> ALTER TABLE test_table ADD col3 NUMBER;
 
Table altered.
 
SQL> SELECT OBJECT_NAME, STATUS FROM USER_OBJECTS WHERE OBJECT_NAME = 'TEST_PROC';
 
OBJECT_NAME STATUS
----------- -------
TEST_PROC   VALID

However, changing the data type of the col1 column, which the test_proc procedure depends on in, invalidates the procedure:

SQL> ALTER TABLE test_table MODIFY col1 VARCHAR2(20);
 
Table altered.
 
SQL> SELECT OBJECT_NAME, STATUS FROM USER_OBJECTS WHERE OBJECT_NAME = 'TEST_PROC';
 
OBJECT_NAME STATUS
----------- -------
TEST_PROC   INVALID

Running or recompiling the procedure makes it valid again, as shown in the following example:

SQL> EXECUTE test_proc
 
PL/SQL procedure successfully completed.
 
SQL> SELECT OBJECT_NAME, STATUS FROM USER_OBJECTS WHERE OBJECT_NAME = 'TEST_PROC';
 
OBJECT_NAME STATUS
----------- -------
TEST_PROC   VALID