Leen Ammeraal is a retired lecturer of Hogeschool Utrecht, The Netherlands, where he was employed from 1977 to 1998. He has a degree in mathematics at University of Technology Delft, The Netherlands. He worked as a programmer and mathematician at Akzo Research and Engineering, Arnhem, The Netherlands, from 1961 to 1972 and did research work on compilers from 1972 to 1977 at Mathematical Centre, Amsterdam. He wrote many books for Wiley. Some of his Wiley books have been translated into other languages. Kang Zhang is a Professor in Computer Science and Director of Visual Computing Lab at the University of Texas at Dallas. He received his B.Eng. in Computer Engineering from the University of Electronic Science and Technology, China, in 1982; and Ph.D. from the University of Brighton, UK, in 1990. He held academic positions in the UK and Australia, prior to joining UTD. Zhang's current research interests are in the areas of visual languages, graphical visualization, and Web engineering; and has published over 130 papers in these areas. He has taught computer graphics and related subjects at both graduate and undergraduate levels for many years. Zhang was also an editor of two books on software visualization.