Cognos allows direct connection to certain version controlling software (Visual Source Safe being the most popular) for Framework Manager. However, there is no direct mechanism for the reports.
The following methods are seen in different organizations for Version Controlling of the reports:
Copy the report specification to clipboard, save it as an XML file, and store it in the version controlling system.
This method allows easy comparison to prior versions of the report, and hence is good for code review during any changes.
However, it can be tedious. Also, restoring to older version needs to be done one report at a time. This also breaks any existing report views defined at the target location.
Export the whole suite of report and store the export file (ZIP format) in the version controlling system.
This is less tedious than prior one as only one file is created for whole suite of reports.
Reverting back to an older and stable state is easy. (Entire suite is reverted back so you can bring the system back to older and stable state – like baseline)
However, this method is not particularly useful while troubleshooting a report to check what changed in it over the versions.
Use of third party tools.
It is possible to hook up to the content store to retrieve the information. There are some third-party tools available that use this method to retrieve report specification and do certain jobs.
You can consider the tools like MotioCI to automatically record the report versions and track changes. They also allow you to revert to older versions. (More information can be found on: http://www.motio.com/products/ci/overview.do)