Marti A. Hearst Chandu Karadi Cat-a-Cone: An Interactive Interface for Specifying Searches and Viewing Retrieval Results using a Large Category Hierarchy. 246-255 1997 conf/sigir/97 SIGIR db/conf/sigir/sigir97.html#HearstK97 SIGIR1997/P246.pdf http://doi.acm.org/10.1145/258525.258582