3-5


role of the query modifier is specifically identified with automatic

query optimization.

         In evaluating the performance of~a document retrieval system,

one must attempt to isolate the effect of the critical variables

which determine system behavior.  The formalization of the notion of

request optimality leads, then, to the ability to measure accurately

the behavior of the indexing function under a given query-document

matching relation, since performance variations due to the malformation

of a search request can be eliminated.   In this context, then,

optimization can be a powerful evaluation tool for testing index

language devices.


2.  Request Formulation


         The process of search request formulation in a document

retrieval system is a complex one and~depends on particular attributes

of the requestor, such as his acquaintance with the reference

collection, his knowledge of the indexing and searching functions of

the system, his familiarity with `the topic matter being searched, his

personal preferences as to vocabulary, style, etc.  In effect, each

user must must make a statistical decision based on his individual

experience as to what formal request &tatement is most likely to

produce results useful to him.  It can be assumed, therefore, that

the a priori likelihood that a user!s search request actually

satisfies his information needs varies over a wide range for a

typical user population.  For example, some users will be able to