Chapter 5: Realizing a Metadata Framework 167 For example, video objects can be considered composite objects containing a series of still images and an audio track (and optionally, subtitles, interactive components, etc.). Using virtual objects that iden- tify a video sequence, metadata properties can be given to any frag- ment of the video, instead of the hierarchical objects. Then, a whole video has its own metadata properties, certain sequences have their own metadata, and the audio track can have its own properties. For instance, a video clip can be divided into chapters that all have their own titles and perhaps even authors. To achieve this goal, we need to be able to give these chapters, or fragments of the object, unique identifi ers. When we can identify the fragment, that fragment may have all metadata attributes that are available to any object. All that is needed here is to give these individual video fragments a unique URIs to identify them and defi ne a is part of relationship with the whole video clip. Using a relation is not strictly needed for storing metadata, but it is useful in that it helps fi nd the parts later by using any of the fragments as a key. Basically, this means that we must have a method to create unique identifi ers, URIs, for pointing inside other objects. W3C has defi ned XPointer to identify fragments of XML docu- ments. Since most objects are not XML, we must defi ne a similar method for these objects, too. 5.6.10 URIs for Fragments To our framework, all URIs are just unique strings. There is no special meaning in the URIs, and applications are free to use them as they like as long as these strings are unique. However, to ensure interoperability between applications, there must be a common language to the frag- ments of objects. This is yet another part of the ontology creation. 24 Our approach is to use existing XML technologies, such as XPath 25 and XPointer, as a basis for a fragment URI. In all cases, for all meta- data objects the fragment (“#”) part of URI is used to indicate the fragment. This section gives an outline on how the common language might be developed. For all objects, the fragment (“#”) part of the URI is used to indicate the fragment. 5.6.10.1 XPointer for XML Documents XPointer Framework is a W3C recommendation for fragment identi- fi ers for any resource that has media type of text/xml or one of other 24 http://www.w3.org/TR/xpath 25 http://www.w3.org/TR/xptr-framework/