Each MSS file is owned by a single user (indicated by the MSS file's scientist number) and is charged to a project number. In addition, the user name (UCAS account) of the user who writes the MSS file is kept. The user name may not match the scientist number if the MSS file ownership has been changed. MSS file ownership may be changed by sending a request to CISL Customer Support (see CISL Customer Support web site for contact methods).

Files are owned by the user who wrote them. Ownership of a file is not based on the directory in which the file resides. In other words, user JOE can write a file with the pathname /LEE/DATA, but JOE still owns the file. Such files will appear in listings of /LEE, but charges will be made to the project set by the creator, JOE. Both JOE and LEE will receive purge notices (see Chapter 5, MSS File Life Cycles for more information).