This issues was faced by a developer, who asked for the solution, so here is something can be done at database level -

[a]
Create an Oracle profile and limit the number of sessions per database user, for example:

sql> CREATE PROFILE <profilename> limit SESSIONS_PER_USER 1;
sql> ALTER USER <username> <profilename>;
sql> ALTER SYSTEM SET RESOURCE_LIMIT=TRUE;

Using this approach, please be aware that dead connections will not always be detected by the database immediately, so users might occasionally not be able to login even a single time until a database administrator has killed their session. Also, they will not be able to login to two different computers at the same time.

[b]
Another workaround could be to write a windows program using the FindWindow() or EnumWindows() API functions to make sure that the Siebel Application is not started a second time. Please note that it is out of scope of Siebel Technical Support to provide such a program. This approach however, could fail, if users discover that they can still start the Siebel Application directly, rather than using the custom program.
[c]

Last, but not least, you could use scripting in the application_start and application_close event and keep the status of an active session in the database (or a local file), not allowing two sessions to be started. This again will require manual intervention if the application was not closed down properly.

Readers, please lets us know if there any other way to do this..

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