VIII -1


              VIII    An Experimental Investigation of
                    Automatic Hierarchy Generation

                G. Blomgren, A. Goodman, and L. Kelly


Abstract

     In automatic or semi-automatic document retrieval systems, a hierarchical

arrangement of concepts or terms affords modification of a query in three

~~ys :  generalization, specialization, or expansion with synonyms.

Hierarchies are u~ually constructed manually.   A method for automatic

~eneration of hierarchies is proposed, and experimental results are presented.


1.  Introduction

     An automatic or semi-automatic document retrieval system usually

includes a thesaurus of concepts or terms which is used to expand queries.

For a given query, thesaurus entries which are similar to terms in the query

are added to its vector of terms.  The search for relevant dcc~nnents then

continues with the expanded query [5,6,7].

     Some systems, such as SM~RT at Harvard, employ a hierarchical arrange-

ment of concepts or terms to modify queries.[3]   Such an arrangement connects

concepts by `tparent-sont1 and t1brother-brother1 relationships.   A parent

concept is more general than its sons; brothers share an equivalent ranking.

Thus a query may be generalized by addin~ to its vector of terms the

parents of those terms; contrariwise, a query may be specialized by adding

the sons of its terms.  The addition of brothers represents inclusion of

similar terms. [5]