LEX DE HAAN studied applied mathematics at the University of Technology in Delft, the Netherlands. His experience with Oracle goes back to the mid 1980s, version 4. He worked for Oracle Corp. from 1990 until 2004 in various education-related roles, ending up in Server Technologies (Oracle product development) as senior curriculum manager for the advanced DBA curriculum group. In that role, he was involved in the development of Oracle9i and Oracle Database 10g. In March 2004, he decided to go independent and founded his own company, Natural Join B.V. (http://www.naturaljoin.nl). From 1999 until his passing in 2006, he was involved in the ISO SQL language standardization process as a member of the Dutch national body. He was also one of the founding members of the OakTable network (http://www.oaktable.net). He wrote the well-received Mastering Oracle SQL and SQL*Plus (Apress, 2005).

TOON KOPPELAARS studied computer science at the University of Technology in Eindhoven, the Netherlands. He is a longtime Oracle technology user, having used the Oracle database and tool software since 1987. During his career he has been involved in application development (terminal/host in the early days, GUI client/server later on, and J2EE/web development nowadays), as well as database administration. His interest areas include performance tuning (ensuring scalability and SQL tuning), architecting applications in a database-centric way, and database design. Within the database design area, the mathematical specification and robust implementation of database designs—that is, including the data integrity constraints (often referred to as business rules)—is one of his special interest areas. He is employed as a senior IT architect at Centraal Boekhuis B.V., a well-known Oracle shop in the Netherlands. Toon is also a frequent presenter at Oracle-related conferences.