This book makes an important contribution to the development of GIS at the leading edge of computing technology. It shows how the principles and technologies of object-oriented programming, distributed processing and internet protocols can be embraced to further the reliability and interoperability of datasets for the GIS profession. The book describes the central concept of an interface specification between the data consumer and producer- the Virtual Data Set (VDS). It then examines the abstraction steps involved with two examples, continuous field representation and modeling uncertainty. The final part of the book looks at implementation, describing how the VDS can be implemented with Java and other object-oriented distributed computing environments.