TAPIO LAHDENM#196;KI, MSc, consults on database performance and teaches product-independent index design courses. He worked for IBM for more than thirty years as a database specialist and was IBM's principal author of the company's global courses for DB2 (for z/OS) performance.MICHAEL LEACH, BSc, is a relational database consultant. He retired from IBM with twenty years' experience teaching application and database classes at IBM locations worldwide. Both authors have seen their material translated into many languages for widespread use. Their approach to index design has been successfully applied in numerous performance-critical systems.