Chapter 4: Metadata Magic 95 4.5.1 Tracing and Recall The simplest way to use metadata is simply to store additional informa- tion which describes the content and actions performed on the object. This is particularly benefi cial for content formats (such as images and video), which do not contain machine-readable textual data. The additional information is also used for providing information for data catalogues. Furthermore, metadata can describe the creator of the content and the history of data, such as the original source of the data and any subsequent transformations that can aid in tracing the content lifecycle. The benefi t of history information is that it assists the user in recalling the context (for example, people, event, and location) as well as helping content management systems to trace the changes between multiple copies of the same content. 4.5.2 Searching Searching is perhaps one of the most typical examples of operations that benefi t from metadata. When metadata is used for searching, it aims at decreasing the amount of work required for formulating the query and enhancing discovering by rapidly providing only relevant and useful results. Essentially, this is due to the fact that it is easier for a computer to search for symbols than recognize objects and features from raw multimedia content. Looking up “Person: John Smith” from an indexed database is thousands of times faster than scanning images for faces and matching those to Smith’s facial features. Some search mechanisms that metadata facilitates include: • Search-by-example allows users to search without defi ning explicit keywords. Instead a user can select an object that provides an example of content that the user wishes to discover. For example, this allows fi nding a video of football games by showing a clip of a Tottenham game. This can also be referred to as relevance feedback. • Creating personalized searches that are based on the user’s prior behaviour or activities. • Ad hoc searches for content that is not indexed. For instance, while walking on the street, the user could ask the device to fi nd the latest message from Eddie that contains Angie’s new telephone number. • Collaborative searching is using other users’ previous searches on a same or similar topic. It can be based on, for instance, examining