Chapter 5: Realizing a Metadata Framework 135 A deeper challenge is due to the changes made in the content objects themselves. Resolving the issues that arise requires both syn- chronization and version control. This leads us to philosophical issues, such as defi ning the similarity of two objects. For instance, when a photo is edited for colour balance, is it the same as the original version? In case the original fi le is replaced in the process, it obviously is the same from the storage system’s point of view. However, as far as synchronization is concerned, what should be done with the original photo stored in a mobile device, and the edited version in the desktop computer? Should the original be deleted? From the user’s point of view, this may or may not be the case. A partial solution is to delete nothing until explicitly instructed so by the user, but to keep control of all changes and allowing an indefi - nite number of undo operations. The problem in these cases is the ever more rapidly growing amount of content, and so fi nding the suit- able version of a photo for a slideshow, for instance. 5.2.4 Backing Up Important and valuable personal belongings have always been kept safe by the means of safes, safe deposits at banks, etc. Digital content is, or should be, no exception. When discussing the features of indi- vidual content objects, one of the most important of them is, not sur- prisingly, personality. In many cases, content has not become personal for free: in order to create or personalize it, you may have had to put in some effort in doing so. If the content is lost or damaged, the changes made by you are also lost; there is no authority that can restore it. The solution is storing the content, more or less frequently, to an alternative storage medium. Backing up data is a typical application of synchronization. ONE SERVER TO RULE THEM ALL Angie thinks her dad has gone nuts. He had bought yet another network disk for their home network. As if they would not have enough storage already, with four computers in the house – Dad’s Mac, the media centre Mac in the living room, Adam’s game PC, and Angie’s own laptop. Everyone had access to each other’s computer’s fi les, although Angie carefully kept her own personal fi les away from her public folder. They had devised a cross-backup strategy: all their videos, images, and music were stored in the media centre and backed up in the offi ce Mac. In addition, her dad sometimes burned DVDs of the family albums and sent copies to Uncle