Do users prefer selection from a menu or specification of keywords to retrieve documents? We tried two experiments, one using an on-line library catalog and the other an on-line news wire. In the first, library users could either issue keyword commands to see book catalog entries, or choose categories from a menu following the Dewey Decimal classification of the books. In the second, news wire users could read Associated Press news stories either by posting a keyword profile against which all

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... ories were matched, or by selecting them from a menu of current news items. For the library users, keyword searches were clearly preferred, by votes of 3 and 4 to 1; for the news stories, retrieval by keyword search is 50% less common than menu choice. We suggest that the difference is based on the degree of user foreknowledge of the data base and its organization. Menu-type interfaces tell the user what is available. If the user already knows, as in the library where a majority of the users have a particular book in mind, then the menu is merely time-consuming. But when the user does not know what is available (almost the definition of "news" is that it is new, and unpredictable), the menu is valuable because it displays the choice.