In this article the author sketches the significant relationships between research and system design in the field, and outlines research approach to the Third Generation Online Public Access Catalog (OPAC). The first part describes the so called "Third Generation" OPAC . Then the selected results of OPAC use and user studies in the early 80's as well as their impact on the design of the second generation OPAC that is most popular in today's libraries are presented. And finally two research approaches in improving user interface and subject searching capacity are suggested.