1. An information system comprising: means for accessing a first collection of data items; retrieval-request means adapted to enable a user of said information system to identify a class of data items said user desires to retrieve from a remote information system, wherein the user identifies said class of data items by reference to a set of one or more examples, said examples being data items in said first collection; an information agent responsive to the retrieval-request means and adapted to prepare an initial query for transmitting the user's request to a remote information system, said query including a label designating a data item-category desired for retrieval, said information agent comprising a classifier adapted automatically to assign a category to said set of examples identified by the user, the information agent being adapted to include in the initial query a label corresponding to the assigned category; output means for outputting the initial query prepared by the information agent; input means for receiving information identifying data items retrieved by a remote information system in response to a query output by said output means; presentation means for presenting the first user with said information identifying the data items retrieved by the remote information system; and selection means for enabling the first user to make a selection from among the data items retrieved from the remote information system in response to a query; characterized in that: the information agent maintains an inventory of categories, labels, and bindings associating labels and categories with each other, and is adapted to include, in the initial query, the label having the strongest binding to the assigned category; and the information agent is responsive to the selection means whereby to change the strength of bindings between labels and categories dependent upon the user's selection.