MYDB =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = mydbserver.example.com)(PORT = 1521))
    (CONNECT_DATA =
      (SERVICE_NAME = mydbservice)
    )
  )
  (USER = myusername)
  (PASSWORD = mypassword)

MYDB_ALIAS =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = mydbserver.example.com)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVICE_NAME = mydbservice)
    )
  )
  (USER = anotheruser)
  (PASSWORD = anotherpassword)