MS SQL Server to Oracle

Question

I am going to write all of the steps here that I have used trying to connect Oracle to MS SQL Server, so that others may benefit. I spent a few days using the following document, but in the end it turned out to be fairly incomplete, and I was frustrated by the amount of time that I had wasted.
"Using Heterogeneous Services"
http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96544/admin.htm#169356
This document could be substantially improved with just three additions:
1. A clear distinction between tasks which are to be performed on the MS SQL Server hardware vs. the Oracle server,
2. More meaningful naming conventions in the examples instead of "Sybase_sales" and "SalesDB", that give you an idea of whether they refer to an Oracle Instance, a SQL Server Database, or something else,
3. Some mention of Oracle Transparent Gateway, and the fact that it needs to be installed for any of this to work.
I fully recognize the fact that I am still somewhat in the dark because I havn't gotten it to work yet; however, I wanted to mention that I began working for Oracle Consulting in 1990, and have been an independent Oracle Consultant since 1995. Therefore; the documentation for Heterogeneous Connectivity has not been adequate for a somewhat experienced Oracle developer.
Below are the steps that I have performed:

Answer 1

How to use TG4MSQL with MS SQL Server Instances
Microsoft introduced with MS SQL Server 2000 the concept of "instances".
All older releases (6.5 or 7.0) running on the same machine as a
SQL Server 2k act as a DEFAULT instance. The same is true for the first
installation of a MS SQL SERVER 2k on a PC.
All further installations of MS SQL Server 2k on the same machine are
named instances; this means a name must be provided during the
MS installation routine for this instance.
How to configure TG4MSQL in detail is described in
Note 231458.1 named HOW TO SETUP TG4MSQL
If there is only a default instance of MS SQL Server running, the parameter
HS_FDS_CONNECT_INFO is configured as:
HS_FDS_CONNECT_INFO = <server name>.<database name>
Method I:
This method is the fastest, but might cause problems if the MS SQL Server
is not listening on the default port. Give it a try, but if this method
causes troubles, please proceed to method 2.
The simplest way to work with instances is to specify the connect details in
the init.ora of the TG4MSQL.
The connect info contains the server name of the MS SQL Server, the instance
name and the database of the instance:
HS_FDS_CONNECT_INFO="<SERVER NAME>\\<INSTANCE NAME>.<DATABASE>"
If the server name is SQLSERVER and the instance name is instance2, the connect
string to the Northwind database looks like:
HS_FDS_CONNECT_INFO="SQLSERVER\\instance2.Northwind"
Similar to the description above is the connect information:
HS_FDS_CONNECT_INFO="SERVER=<SERVER NAME>\\<INSTANCE NAME>;DATABASE=<DATABASE>"
(HS_FDS_CONNECT_INFO="SERVER=SQLSERVER\\instance2; DATABASE=Northwind" )
Method II:
This method can be used also to connect to a MS SQL Server not listening
on the default port 1433.
It is based on using ALIASes:
If the MS SQL Server port or an alias is used instead of the servername,
the following registry key will be checked:
HKEY_LOCAL_MACHINE\
SOFTWARE\
Microsoft\
MSSQLServer\
ConnectTo
Microsoft provides a Client Configuration Tool to pass all parameters into the
registy (for example run PROFILER, click on options and execute the
Client Config Tool).
If there is no SQL Server client installed on the gateway machine, an idea
could be to configure it on the MS SQL Server, export the registry key and
import it again on the TG4MSQL machine. Please contact Microsoft about details.
This registry key is responsible for the connection details to the MS SQL Server.
While dealing with INSTANCEs or changing the MS SQL Server to listen on a
networking port other then 1433 (MS default port for SQL Server) the SUBKEY
ConnectTo is used to verify the connect details.
The Micrososft Client Configuration Utility configures ALIASes.
To work with a second instance of the MS SQL Server, an ALIAS for this
instance must be added.
This tool asks to choose a Serveralias (a name you can define on your own)
and to specify the Server name.
Normally the server name is equal to the IP address or to the hostname of
the MSQ SQL Server machine. But while working with instances the instance name
must be specified as well. The instance name is separated by TWO back slashes
from the server name.
For a better explanation the value for for the Server alias is "instance2alias" and
for the server name it is MSSQLSERVER. The sample name of the second instance is
INSTANCE2.
In the config tool type instance2alias into the entry filed of the server alias
and type MSSQLSERVER\\INSTANCE2 as server name.
Furthermore the default option is to figure out the MS SQL Server Ports dynamically.
If you do not want to detect them automatically, add the port of your SQL
Server is listening on; default is 1433. For this example port 1868 is used.
After applying this the ALIAS is saved into the registry:
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSSQLServer\Client\ConnectTo]
and it contains the following connect information:
"instance2alias"="DBMSSOCN,MSSQLSERVER\\INSTANCE2,1868"
The first parameter is the SQL Server alias, the second is a MS key word and
the next value is the hostname delimited by two back slashes from the instance
name.
Comment: Default instances do not have an entry here.
The last parameter is the port if it is not detected automatically.
If you have any questions about creating SQL Server aliases or what to
fill into the according columns, please contact Microsoft Support!
There is also a good note in the MS knowledge base:
Microsoft Knowledge Base Article - 265808
INF: How to Connect to an SQL Server 2000 Named Instance
with the Previous Version's Client Tools
Back to the Gateway configuration:
Oracle Transparent Gateway is able to work with MS SQL Server instances;
instead of specifying the <servername> at HS_FDS_CONNECT_INFO, the
<alias> must be specified.
For this example the parameter looks like:
HS_FDS_CONNECT_INFO = instance2alias.master