Check out example codes for "ORA-01157: cannot identify/lock data file 7 - see DBWR trace file ORA-01110: data file 7: 'D:\DOCUMENTOS\BDORACLE\CLASE003.DBF'". It will help you in understanding the concepts better.

Code Example 1

C:\>sqlplus sys/sys as sysdba
SQL*Plus: Release Production on Tue Apr 30 19:07:16 2013
Copyright (c) 1982, 2011, Oracle.  All rights reserved.
Connected to an idle instance.

SQL> startup
ORACLE instance started.
Total System Global Area  778387456 bytes
Fixed Size                  1384856 bytes
Variable Size             520097384 bytes
Database Buffers          251658240 bytes
Redo Buffers                5246976 bytes
Database mounted.
ORA-01157: cannot identify/lock data file 11 – see DBWR trace file
ORA-01110: data file 16: 'E:\oracle\app\nimish.garg\oradata\orcl\test_ts.dbf'

SQL> select NAME from v$datafile where file#=16;

SQL> alter database datafile 16 OFFLINE DROP;
Database altered.

SQL> alter database open;
Database altered.

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