R.G.MILES XHP Consulting Ltd, Gloucester. This book is one of two volumes containing papers for presentation at the British Computer Society Expert Systems 98 conference. This is the annual conference of th the BCS Specialist Group on Expert Systems and is in its 18 year. During its lifetime it has established itself as the premier Expert Systems conference in the UK. The conference is attracting an increasing number of papers world-wide and this year in excess of 70% were from research groups outside the UK. This volume includes all papers accepted for the Technical Stream of Expert Systems 98 and presented at the conference in December 1998. The papers within this stream present innovative, new research work. The companion volume, Applications and Innovations in Expert Systems VI, includes all papers accepted for the application stream of the conference. This stream has become the premier European conference on applications of Expert Systems. The papers accepted for presentation within the Technical Stream cover a broad range of research within Expert Systems and fit into four broad categories: ontological frameworks, knowledge base development, classifiers and neuro-fuzzy systems. The award for best Technical paper has been made to David McSherry, from the University of Ulster, for his paper entitled "Strategic Induction of Decision Trees".