Even considering only content descriptions, the semantic relationships among index terms are of several different types and can serve different purposes. Actually, the very fact that one item was explicitly coded while the other was not strongly suggests that the clip is not a good exemplar of the uncoded concept. In addition to these generic relationships which apply to many different index categories, there are also interesting specific relationships that hold only between members of particular index categories. Content descriptions include index terms drawn from categories such as settings, activities, people, and things. There exist significant relationships between settings and activities, between activities and people, and between activities and things.
Many activities stereotypically occur in particular settings.
A particular activity will generally suggest particular types of people and things that might be involved in the activity. Like most of the earlier generic relationships, these specific relationships do not support computer-controlled inference. However, as described in the next section, all these relationships, can be exploited by the retrieval system to provide support for user-directed search through a large conceptual space. Discussions with video producers indicate that they are far more concerned about a system returning too few clips than about getting too many. The strategy that we have implemented to retrieve clips from our stock video library can best be characterized as user-directed search.