Syntactic Approaches to Automatic Book Indexing

SYNTACTIC APPROACHES TO AUTOMATIC BOOK INDEXING Gerard Salton Department of Computer Science Cornell University Ithaca, NY 14853 ABSTRACT Automatic book indexing systems are based on the generation of phrase struc- tures capable of reflecting text content. • Some approaches are given for the automatic construction of back-of-book indexes using a syntactic analysis of the available texts, followed by the identifica- tion of nominal constructions, the assign- ment of importance weights to the term phrases, and the choice of phrases as index- ing units. INTRODUCTION Book indexing is of wide practical interest to authors, publishers, and readers of printed materials. For present purposes, a standard entry in a book index may be assumed to be a nominal construction listed in normal phrase order, or appearing in some permuted form with the. principal term as phrase head, Cross-references ("see" or "see also" entries) between index entries are also normally used in the index. Excerpts from two typical book indexes appear in Fig. 1. Attempts have been made over the years to mechanize the book indexing task, based in part on the occurrence characteris- tics of certain content words in the docu- ment texts [Borko, 1970], and in part on more ambitious syntactic methodologies. [Dillon, 1983] However, as of now, com- pletely viable automatic book indexing methods are not available. Two main This study was supported in part by a grant from OCLC Inc.. and in part by the National Science Foun- dation under grant [R[-87-02735. research advances may, however, lead to the development of improved automatic book indexing procedures. These include the generation of advanced syntactic analysis procedures, capable of analyzing unrestricted English texts, as well as the construction of powerful automatic indexing systems using sophisticated term weighting systems to assess the importance of the indexing units. [Salton 1975a, 1975b] By joining the available linguistic procedures with the available know-how in automatic indexing, satisfactory book indexing sys- tems may be developed. AUTOMATIC PHRASE CONSTRUCTION Book indexing systems differ from standard automatic text indexing systems because complex, multi-word phrases are normally used for indexing purposes rather than the single term entries that are pre- ferred in conventional automatic indexing systems. The phrase generation system described in this note is based on an automatic syntactic analysis of the avail- able texts followed by a noun-phrase iden- tification process using parse trees as input and producing lists of nominal construc- tions. The parsing system used in this study is based on an augmented phrase structure grammar, and was originally designed for use in the EPISTLE text- critiquing system. I (Heidorn, 1982, Jensen, 1983) A typical document abstract is shown 1 The writer is indebted to the IBM Corporation and to Dr. George Heidorn for making available the PLNLP parsing system for use at Cornell University. 204 in Fig. 2, and the output produced by the syntactic analysis program for sentence 2 of the document is shown in Fig. 3. It may be noted that the syntactic output appears in the form of a standard phrase …

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