• In the code world, an index could still be a source file that is part of the source system when compiled and or executed as part of the application. Therefore, it would be added to the repository and tracked line anything else. So, for example. The index file would be a configuration file that fed into a function within the application to help the application make a decision on what to do with the data. That function may be the actual algorithm that defines how the data is stored, how it's written, and how it's searched when the user wants to query the data. 

    However, there are plenty of cases where configuration files are provided outside the source that are part of the repository that can be altered or allowed to provide additional configuration from the end user to add more functionality. The issue here is that configuration file has no default in the source with SQL Server and is not required to run.