114 Personal Content Experience: Managing Digital Life in the Mobile Age matically from her phone, surrounding devices, and network services available at the time and location where the image was shot. She had earlier entered the Availability and Status fi elds by hand for the pur- poses of the presence application, but the data have been reused in the camera application without additional user effort. Comparing this information to EXIF data stored by a digital still camera (Figure 4-3), one immediately notices a difference in abstraction level. Further events in the life of the media object can also be recorded in the fi le context. Editing, viewing, messaging, and organizing the fi le can all leave not only interaction history, but also context history, which can be signifi cant for later analysis. For instance, people often look for e-mail attachments, not by their names or their content, but by the name of the sender. It can be benefi cial and interesting to recover the communication routes our important fi les have travelled. In our photo example, the Transfer history metadata fi eld shows how Angie’s mother had received the fi le in a multimedia message, sent it for printing, and fi led it for later viewing. This information can be used later to search for the photo when she cannot fi nd the fi le but remembers that she received it from Angie. 4.7.2 Elements of Context Context is a vague, hard-to-defi ne concept (like metadata) that can be used to refer to almost arbitrary kinds of information. To highlight various elements of context, let us take a look at a more detailed cat- egorization (ePerSpace 2004) and study what characteristics would be valuable for later use: • Environmental context, which describes the entities around and the environment where the user and the device currently are. The information describes, for example, other devices, other users, brightness, temperature, and humidity. • Social context defi nes the relationships between users nearby. It can contain information about friends, co-workers, relatives, and so forth. • Spatio-temporal context means the location in the real world at a certain moment of time. • Task context describes information related to on-going tasks, for example, based on the calendar information. • Personal context refers to physiological (such as blood pressure and pulse) and mental context (for instance mood and stress) related to the user.