In response to the motivations discussed above, many educators have turned to network-based systems that allow data sharing between project partners (i.e., student and teacher or student and student). Such systems have come to be called Computer-Supported Cooperative Work (CSCW). However, sharing data in an easy and secure way is not well supported by current operating systems. In UNIX a file can belong to a group of users, each of whom share permission to access the file. This can be used to keep other people from reading or writing that file, but all members of the group have free access. One possible configuration would be to put one teacher and one student in a given group. It would be advantageous to put each of these teacher-student groups into a superordinate group for the entire class. Unfortunately, UNIX has a limitation that doesn't support this desirable feature. Though MAC OS 7 would support this, UNIX does not provide hierarchies for groups, and the number of groups per user is also quite limited (maximum of 16 groups, kernel specific). So at the level of the operating system, sufficient sharing cannot be accomplished. One solution is to use a program with super-user permission, which can change ownerships (e.g., aegis [Mil95]). Another way to change ownership is to use an electronic mail system (since mail is always owned by the receiver). There are, of course, application systems (e.g., Lotus Notes) that do support data sharing (including version management). In the long run, we can expect support at the operating system level as well.