In order to allow files structures at different locations to be synchronized, a folder tree descriptive of each set of folders is created and stored at a plurality of locations. On subsequent interconnection of the two locations a new tree is created for each location and the earliest of the old trees is used to determine which files, folders or paths of the two locations have been amended. This enables deletion or re-synchronization of files between the two locations even though files may have been worked on at different locations and at different times.