Context awareness refers to the apability of an appli ation or a servi e be-

ing aware of its physi al environment or situation (i.e., ontext) and respond-

ing proa tively and intelligently based on su h awareness (1, 7, 11). With

re ent developments in omputer hardware, software, networking, and sensor

te hnologies, ontext awareness be omes one of the most ex iting trends in

omputing today that holds the potential to make our daily lives more pro-

du tive, onvenient, and enjoyable. For example, a tour-guide servi e gives

tourists suggestions on the attra tions to visit by onsidering their urrent

lo ations, preferen es, and even the prevailing weather onditions.