Once we had a need of accessing a table on an Microsoft SQL Server database from an Oracle database. Thus we had to install Oracle Transparent Server on the computer hosting SQL Server. Oracle Transparent Services is a kind of adapter for non-Oracle servers and allows access to it through database link. During the instalation of Oracle Transparent Server you have to choose modules dedicated to particular databases. The modules can translate calls to some functions and allows to call a T-SQL stored procedure from Oracle.
Oracle Transparent Server can be downloaded from http://www.oracle.com/technology/software/products/database/oracle10g/htdocs/10201winsoft.html
Description of its solution can be found here: http://oracle-apps-dba.blogspot.com/2008/04/oracle-transparent-gateways-general.html
Instalation instructions are here… : http://oracle-apps-dba.blogspot.com/2008/04/oracle-transparent-gateway-for-ms-sql_16.html
However, most of the configurations files were located in the directory network\admin and not in tg4msql\admin as described
I found that access to the data is slow – the simplest queries last for 4 seconds. However, increasing the efficiency is another topic.