This paper differs from our earlier work (Schafer, Konstan, & Riedl, 1999) in several key ways. First, the examples have been
updated and expanded to better reflect the rapidly expanding field of recommender systems. Second, the taxonomy has been
modified and expanded to more accurately encompass all of the aspects of recommendation technology and to be appropriate for a
data mining audience. Third, the opportunities section has been expanded to feature additional ideas and to reflect the current state
of the field. Finally, several new sections have been added, including sections relating recommender systems to traditional
marketing techniques and a discussion of privacy concerns.