1. An information system comprising: an accessing unit adapted to access a first collection of data items; a retrieval-request unit 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 unit and adapted to prepare an initial query for transmitting the user's request to a remote information system, said information agent comprising a classifier adapted automatically to determine a data-item-category applicable to said set of examples identified by the user; a coder adapted to select a label from among a set of one or more labels associated with the data-item-category determined by the classifier, the information agent is adapted to designate the category of data item desired for retrieval by including in the initial query the label selected by the coder; an output unit adapted to output the initial query prepared by the information agent as a query; an input unit adapted to receive information identifying data items retrieved by a remote information system in response to the query output by said output unit; a presentation unit adapted to present the user with said information identifying the data items retrieved by the remote information system; and a selection unit to enable the first user to make a selection from among the data items retrieved from the remote information system in response to a query; wherein the information agent maintains an inventory of categories, labels, and bindings associating labels and categories with each other, and the coder is adapted to select, from among the set of one or more labels associated with the data-item-category determined by the classifier, the label which the inventory indicates has the strongest binding to said determined data-item-category; and the information agent is responsive to the selection unit to increase the strength of the binding, between the label included in the initial query and the data-item-category determined by the classifier, relative to the strength of the binding between said determined data-item category and other labels of said set of labels associated with said determined data-item-category, when the user's selection indicates that data retrieved by said remote information system in response to the initial query of the user conforming to the user's initial query, and to reduce the strength of the binding, between the label included in the initial query and the data-item-category determined by the classifier, relative to the strength of the binding between said determined data-item category and other labels of said set of labels associated with said determined data-item-category, when the selection of the user indicates that data retrieved by the remote information system in response to the initial query of the user does not conform to the user's initial query.