-- Host string is the name you assign for tns COnnectivity in tnsnames.ora
-- these entries typically identify the machine and portnumber and sid of the database you
-- are trying to connect.
-- for example i am using these entries in tnsnames.ora
-- here 'mutation' i have named the hoststring as mutation
-- i can name anything i want

bash-2.03$ tail -7  tnsnames.ora
mutation =
  (DESCRIPTION =
        (ADDRESS_LIST =
        (ADDRESS = (PROTOCOL = TCP)(HOST = myhost )(PORT = 1521)))
        (CONNECT_DATA =
        (SERVER = DEDICATED)
        (SERVICE_NAME = mutation))))

-- 
-- if the client and database are in same machine, you dont need a hoststring.
--

bash-2.03$ sqlplus mag/mag

SQL*Plus: Release 9.2.0.4.0 - Production on Tue Mar 22 08:24:34 2005

Copyright (c) 1982, 2002, Oracle Corporation.  All rights reserved.


Connected to:
Oracle9i Enterprise Edition Release 9.2.0.4.0 - 64bit Production
With the Partitioning option
JServer Release 9.2.0.4.0 - Production

mag@mutation_mutation > exit
Disconnected from Oracle9i Enterprise Edition Release 9.2.0.4.0 - 64bit Production
With the Partitioning option
JServer Release 9.2.0.4.0 - Production


-- 
-- if you intend to use the hoststring ( for a local database or remote database)
-- you should use it like this.
-- by this your sql cleint will talk to the database identified by hoststring.

bash-2.03$ sqlplus mag/mag@mutation

SQL*Plus: Release 9.2.0.4.0 - Production on Tue Mar 22 08:24:54 2005

Copyright (c) 1982, 2002, Oracle Corporation.  All rights reserved.


Connected to:
Oracle9i Enterprise Edition Release 9.2.0.4.0 - 64bit Production
With the Partitioning option
JServer Release 9.2.0.4.0 - Production

mag@mutation_mutation > exit
Disconnected from Oracle9i Enterprise Edition Release 9.2.0.4.0 - 64bit Production
With the Partitioning option
JServer Release 9.2.0.4.0 - Production
bash-2.03$