The global database name consists of the user-specified local database name and the location of the database within a network structure.
The DB_NAME initialization parameter determines the local name component of the database name, and the DB_DOMAIN parameter, which is optional, indicates the domain (logical location) within a network structure.
The combination of the settings for these two parameters must form a database name that is unique within a network.For example, to create a database with a global database name of test.us.acme.com, edit the parameters of the new parameter file as follows:
DB_NAME = test
DB_DOMAIN = us.ooportal.com
You can rename the GLOBAL_NAME of your database using the ALTER DATABASE RENAME GLOBAL_NAME statement.
However, you must also shut down and restart the database after first changing the DB_NAME and DB_DOMAIN initialization parameters
and recreating the control files. Recreating the control files is easily accomplished with the command ALTER DATABASE BACKUP CONTROLFILE TO TRACE.
DB_NAME must be set to a text string of no more than eight characters. During database creation, the name provided for DB_NAME is recorded in the datafiles, redo log files, and control file of the database. If during database instance startup the value of the DB_NAME parameter (in the parameter file) and the database name in the control file are not the same, the database does not start.