Guest Editorial; J. Jing, A. Joshi. Updating and Querying Databases that Track Mobile Units; O. Wolfson, et al. Mobility and Extensibility in the StratOSphere Framework; D. Wu, et al. Experiences of Using Generative Communications to Support Adaptive Mobile Applications; A. Friday, et al. MODEC: A Multi-Granularity Mobile Object-Oriented Database Caching Mechanism, Prototype and Performance; B.Y.L. Chan, et al.