Chapter 8: Timeshifting Life 337 ing related to automated operations is not visible to users – they cannot understand the relation between the starting point and the result. We may need explanation mechanisms for metadata. One threat that is closely related to automation, user interfaces, and human acceptance, is the proper level of metadata visibility. In other words, how to make it predictable what some metadata-enhanced action will produce? How to make it perceivable to the user what metadata attributes, values, automation, inference, and so forth has resulted in the current view or state. Even though we have discussed how metadata aids managing content, there is another perspective that would merit further study: how could metadata help people to feel better? How could we employ metadata in a manner that makes systems dealing with personal content more calm (Weiser and Brown 1996)? These issues are not yet well understood and are being studied in various fi elds, for instance from the viewpoint of affective computing (Picard 1997). We believe that per- sonal content will have a higher emotional value to a user, and therefore may serve better in affective systems than unfamiliar content. Technology will progress and develop at a pace that easily surpasses many human capabilities. Therefore, we need to seek out new user interface and interaction paradigms and technologies that aid in per- sonal content experiencing while on move. For instance, people cannot pay a lot of visual attention to a device when walking on a busy street, which means that the mobile device UI should support rapid glance and click type of interactions that do not require more than couple of seconds to convey all relevant information. This, of course, requires a lot of technology in the background to select what is relevant in the current context. 8.5 From Databases to Lifebases Many visions of personal content to come include the notion of a memory prosthesis, that is, a system that records and manages every- thing; one example is MyLifeBits (Gemmell et al. 2006). This typical memory prosthesis includes a camera attached to your head-worn display, which is always on, always recording: all you see is seen and stored by the camera – for as long as you are wearing such headgear (Figure 8-2). Likewise, your auditive environment is continuously recorded. A multitude of other data may also be recorded, such as location, physical parameters, sensor readings, and so forth. A mobile phone can also be geared towards a memory prosthesis (Rhee et al. 2006).