The performance of a retrieval system with a file of only a few hundred references can be measured by assessing the relevance of each reference to each of a number of queries. A suitable measure of retrieval performance is then the Recall ratio—the fraction of the relevant references that are...

One technique for searching a Co‐ordinate Index is to compare each reference with a Boolean expression of index terms. This divides the file into retrieved and not‐retrieved references. An alternative is to assign each reference a score calculated from its index terms and to retrieve the N...