Toward a theory of indexing

A theory of indexing helps explain the nature of indexing, the structure of the vocabulary, and the quality of the index. Indexing theories formulated by Jonker, Heilprin, Landry and Salton are described. Each formulation has a different focus. Jonker, by means of the Terminological and Connective Continua, provided a basis for understanding the relationships between the size of the vocabulary, the hierarchical organization, and the specificity by which concepts can be described. Heilprin introduced the idea of a search path which leads from query to document. He also added a third dimension to Jonker's model; the three variables are diffuseness, permutivity and hierarchical connectedness. Landry made an ambitious and well conceived attempt to build a comprehensive theory of indexing predicated upon sets of documents, sets of attributes, and sets of relationships between the two. It is expressed in theorems and by formal notation. Salton provided both a notational definition of indexing and procedures for improving the ability of index terms to discriminate between relevant and nonrelevant documents. These separate theories need to be tested experimentally and eventually combined into a unified comprehensive theory of indexing.