I recommend that everyone interested in "content enrichment" read this 2007 article.
It is presented in a clear, easy to read manner with references. It documents that library staff are still discussing "content enrichment" ideas that are actually 20 years delayed.
The author believed it was necessary for libraries to "heed catalog users' longtime demands for improvements to the searching experience."
The Online Library Catalog
Paradise Lost and Paradise Regained?
University of Michigan
Volume 13 Number 1/2