Excerpts from the Introduction:

Information retrieval is a wide, often loosely-defined term but in these pages I shall be concerned only with automatic information retrieval systems. Automatic as opposed to manual and information as opposed to data or fact. Unfortunately the word information can be very misleading. In the context of information retrieval (IR), information, in the technical meaning given in Shannon's theory of communication, is not readily measured (Shannon and Weaver). In fact, in many cases one can adequately describe the kind of retrieval by simply substituting 'document' for 'information'. Nevertheless, 'information retrieval' has become accepted as a description of the kind of work published by Cleverdon, Salton, Sparck Jones, Lancaster and others. A perfectly straightforward definition along these lines is given by Lancaster: 'Information retrieval is the term conventionally, though somewhat inaccurately, applied to the type of activity discussed in this volume. An information retrieval system does not inform (i.e. change the knowledge of) the user on the subject of his inquiry. It merely informs on the existence (or non-existence) and whereabouts of documents relating to his request.' This specifically excludes Question-Answering systems as typified by Winograd and those described by Minsky. It also excludes data retrieval systems such as used by, say, the stock exchange for on-line quotations.

Many of the techniques I shall discuss will not have proved themselves incontrovertibly superior to all other techniques, but they have promise and their promise will only be realised when they are understood. Information about new techniques has been so scattered through the literature that to find out about them you need to be an expert before you begin to look. I hope that I will be able to take the reader to the point where he will have little trouble in implementing some of the new techniques. Also, that some people will then go on to experiment with them, and generate new, convincing evidence of their efficiency and effectiveness.

My aim throughout has been to give a complete coverage of the more important ideas current in various special areas of information retrieval. Inevitably some ideas have been elaborated at the expense of others. In particular, emphasis is placed on the use of automatic classification techniques and rigorous methods of measurement of effectiveness. On the other hand, automatic content analysis is given only a superficial coverage. The reasons are straightforward, firstly the material reflects my own bias, and secondly, no adequate coverage of the first two topics has been given before whereas automatic content analysis has been documented very well elsewhere. A subsidiary reason for emphasising automatic classification is that little appears to be known or understood about it in the context of IR so that research workers are loath to experiment with it.