1. A method in a computing system for defining a group of people, comprising: providing a visual user interface containing a control for receiving a query string; receiving a query string via the control; using an index on a body of documents to identify documents of the body that satisfy the received query string; accessing a record indicating which documents of the body were accessed by each of a population of people during a foregoing time period to identify people among the population that accessed at least a threshold number of the identified documents during the foregoing time period; and displaying within the visual user interface, in conjunction with the control, information characterizing the people identified.