School of Information, University of California, Berkeley, CA 94720, USA. hearst@ischool.berkeley.edu|School of Information, University of California, Berkeley, CA 94720, USA. hearst@ischool.berkeley.edu|School of Information, University of California, Berkeley, CA 94720, USA. hearst@ischool.berkeley.edu|School of Information, University of California, Berkeley, CA 94720, USA. hearst@ischool.berkeley.edu|School of Information, University of California, Berkeley, CA 94720, USA. hearst@ischool.berkeley.edu|School of Information, University of California, Berkeley, CA 94720, USA. hearst@ischool.berkeley.edu|School of Information, University of California, Berkeley, CA 94720, USA. hearst@ischool.berkeley.edu