150 Personal Content Experience: Managing Digital Life in the Mobile Age computing power and memory capacity compared to desktop PCs. We claim that by fulfi lling the other requirements, this one also is fulfi lled. 5.4.1 Cross Media Challenge and Metadata Ownership Currently, metadata is generally managed by single domain-specifi c applications, most commonly media players. Music players, such as Apple iTunes, take care of tagging songs with metadata attributes about artists, genre, and so on, but they only care about music-related attri- butes. Even worse, each music player has its own metadata manage- ment functionality that might differ slightly from other players. For example, Apple’s popular iTunes media player stores its playlists and song metadata into its own database. No other application can access that data, which results in Windows Media Player or any other MP3 or media player having to store its own metadata into a separate data- base, duplicating or even tripling exactly the same metadata. Not only are system resources, such as storage memory, wasted but maintaining them are much harder. Similarly, all video-related attributes are managed within video players, and still image metadata in image viewers and editors. Some metadata, including fi le creation and modi- fi cation timestamps, are handled by the operating system. Ultimately, there are lots of metadata that no application cares about. Most applications are unaffected by any metadata beyond the content types they primarily deal with. Some music players can link an MP3 song to an image, such as the album cover art image. The same link the other way round is impossible, as there is no image viewer that plays or even knows songs of the album when you are viewing the album cover image. And which application should be responsible for maintaining the link between songs and album covers? What is described above is just a simple association between two content objects in two applications. Many times there are associations between many objects used in many applications. The use case with MP3 fi les received from Eddie during the concert includes links between content objects primarily used in a music player, and in e-mail and calendar applications. Obviously, there cannot be a single application that is responsible for such metadata. To conclude, metadata is rarely specifi c to only one application. One of the great benefi ts of metadata is that it acts as a common language between applications, and therefore facilitates application interoperability. Metadata provides all applications with a means to understand what has happened to any content object before, and