V-35


           I.    Term Weights

                   Weighted Word Stems        >~   Logical Stems
                   Weighted Synonym Classes   »    Logical Synonym Classes

           2.    Document Length
                   Full Summaries (2000 words) >   Abstracts (150 words)
                   Abstracts (ISO words)      »    Titles Only

           3.    Synonym Recognition:
                   Abstracts with Thesaurus   )>   Abstracts Null
                   Summaries with Thesaurus   >    Summaries Null

           4.    Phrase Recognition:
                   Synonym and Phrase         >    Synonym Recognition
                         Recognition                 (Thesaurus) only
           5.    Syntactic Analysis:
                   Syntactic Analysis         »    Word Stem Match
                   Syntactic Analysis         >    Synonym Recognition
                   Syntactic Analysis         -    Statistical Phrase Recognition

           6. Term-Term Associations:
                   Stem-Stem Associations     >    Simple Word Stems
                   Concept-Concept (rhesaurus -    Synonym Recognition
                      Class) Associations
           7.    Manual Indexing:
                   Abstract Stem Matching          Index Term Match
                   lndex Term with Thesaurus  >    Abstracts with Thesorus


»> ::much greater than"
   greater than81       Overoll Evaluation Results
- "about equal to"
           (based on experiments with 4 collections in 3 topic areas)

                                       Fig. 16