An introduction for the knowledge management crowd.
Data By Design in eWeek.
Metadata Helper Applications: Tagging and Entity Extraction from Search Tools.com
Automatic Indexing: A Matter of Degree from Marjorie M. Hlava in the ASIST Bulletin is still the most sober introduction to the topic.
Thanks to Demetri and Ed for links.
Later…
From eContent, Auto-Categorization: Coming to a Library or Intranet Near You!