Creating Oracle Database Link

create [public] database link db_link_name
connect to      user_name
identified by   password
using              Service_name

service_name must be resolvable on the server, for example by entering it into the tnsnames.ora file. A database link is required for various purposes, such as primary key materialized view replication.  This will create one sided link as specified in clause.

For further inform please visit http://download.oracle.com/docs/cd/B28359_01/server.111/b28310/ds_admin002.htm