A paragraph from Wikipedia is not a directory article made me think about our Directories.
Wikipedia encompasses many lists of links to articles within Wikipedia that are used for internal organization or to describe a notable subject. In that sense, Wikipedia functions as an index or directory of its own content. However, Wikipedia is not a directory of everything in the universe that exists or has existed. Please see Wikipedia:Alternative outlets for alternatives.
Basically, describes their Index or Directory as the links contained in a document. Taking into account how hard it is to explain to users our current directory concept, maybe we should do the same thing:
A document will appear in a Directory only if it is created or referenced in the Document Content.
If I delete a link from a document, it will still appear in the directory because it is contained in previous versions.