IRS13 Thesaurus, Phrase and Hierarchy Dictionaries chapter E. M. Keen Harvard University Gerard Salton Use, reproduction, or publication, in whole or in part, is permitted for any purpose of the United States Government. VII-45 superior not always through the introduction of additional matching concepts Cases of the superiority of suffix `5' over thesaurus are also shown in Fig. 28, Q167 and Q323. For example, relevant document 916 matches with five request concepts for both suffix `5' and thesaurus; but since the thesaurus process fails to match with any additional request concepts, and also provides no increase in the weight of any of the matching concepts, document 916 is relegated in rank by non- relevant documents such as 728. In the case of 728, which matches one concept on suffix `5' only, the thesaurus provides additional matching concepts; also since 728 is a short document, it produces a high cosine correlation coefficient and receives the first rank position. In Q323, non-relevant document 316 is matched by four concepts with the thesaurus, and although the thesaurus establishes two additional matches with rele- vant document 34A, this is not sufficient to prevent non-relevant documents from occupying the top rank positions. These examples from the Cran-l collection lead to the question of whether the lessened superiority of thesaurus over stem compared with IRE-3 and ADI is due to a poor thesaurus dictionary or to something in the Cran-l test environment. Evidence strongly points to the latter reason. Cran-l has real user relevance decisions that, on inspection, provide a severe test environment and use relevance decisions that sometimes bear little relation to the stated request. The superiority of suffix `5' over the stem dictionary is not found on IRE-3 and ADI; in Section V, the reason for this is stated to be the terminology employed