Chapter 5: Realizing a Metadata Framework 131 3. A subset of content is included, and the rest of the content is indexed so that its location can be determined, also when mobile. Let us now consider each option in more detail. 5.2.1.1 All Content in a Mobile Device Currently, it is not realistic to assume that all content will be stored and used in a mobile device only. Most likely other content storage formats and types, such as hard disks in PCs, DVDs, memory cards, and PVRs also contain loads of personal content. Therefore, even if all content is stored in a mobile device, a copy of at least a subset of it may also be stored elsewhere or at least used with other devices. However, we can confi dently assume that a signifi cant portion, if not most of personally created content, will be stored (at least temporarily) in mobile devices, since it was created by them in the fi rst place. This, in turn, implies huge challenges in keeping the separate collections and devices in sync. Syn- chronization will be discussed in more detail below. 5.2.1.2 A Subset of Content in Mobile Device In this case, the mobile device contains some subset of the user’s per- sonal content, but is not aware of any other content in any other device, so no synchronization is required. A typical example might be photos taken with a mobile phone’s built-in camera. They sit fi rmly in the phone’s memory card. A special case is a digital camera, which only temporarily stores the images, until transferred to a permanent storage device, after which the camera’s memory card is wiped clean. The same is also true for most mobile devices targeted towards fi tness, such as wristop computers with heart rate measuring capability (section 7.5). 5.2.1.3 A Subset of Content in Mobile Device, The Rest is Indexed This case differs from the above in the sense that even though the mobile device does not have all content, it is aware of its existence and has a link to it and capability to retrieve it when needed. As a result, synchronization is needed in order to provide the mobile device with information on this content available elsewhere. A fourth option can be extrapolated from the above: some content is only in mobile devices (for instance, SMS), some are occasionally transferred to PC (images), some are updated (MP3), some are synchronized (contacts), and some are searched from the device ecosystem.