Paul’s research has focused mainly on the incremental development and maintenance of knowledge-based systems while they are in use, an approach known as Ripple Down Rules (RDR), and his research has had significant industrial impact, with a number of companies having developed services based on RDR, including IBM. In particular, RDR are widely used in medical diagnostic laboratories. Paul was also the head of the School of Computer Science and Engineering at UNSW for 12 years and has been a member of the University Council.