David Arctur is a product specialist at ESRI and is part of the geodatabase development team. He has written for the ""Earth Observation & Mapping Magazine,"" ""IEEE Computer Magazine,"" and ""International Journal of Geographical Information Science,"" He lives in Austin, Texas. Michael Zeiler is a technical writer and data model specialist at ESRI with experience in diagramming GIS concepts, building data models, and programming. He is the author of ""Exploring ArcObjects,"" ""Inside ARC/INFO,"" and ""Modeling Our World,"" He lives in Santa Fe, New Mexico.