5) Version Control: The version control system maintains the various model version source codes and executables. Each model version in the MREP is maintained in Subversion, the free, open-source version control system that manages files and directories over time. A tree of files is placed into a central database. This database is similar to an ordinary file server, except that it remembers every change made to files and directories. This allows the user to recover older versions of data, results, and/or code and to examine their change history.