This essay distinguishes several different kinds of measures of information from each other, noting that differences between them show that our pretheoretical concept of information is multiply ambiguous. Incremental information, conditional information, transmitted information, expected information, and deductive information are discussed. Ten…

Describes the use of relevance feedback to select additional search terms and discusses the extraction of these terms from a maximum spanning tree connecting all terms in the index term vocabulary; retrieval effectiveness for different spanning trees is shown to be similar. Eight references are included. (Author/BK)