W Expressing User Profiles for Data Recharging

are rapidly heading toward a world in which the computing infrastructure will contain billions of devices that are carried or worn by their users as they go through their daily routines. These devices require two key resources to function: power and data. The mobile nature of such devices combined with the economic limitations of size and cost makes it impractical to keep them continually connected to fixed sources of either resource. Mobile devices cope with disconnection from fixed sources of power and data by " caching. " For power, devices typically use rechargeable batteries ; batteries act as a cache of power from the fixed power grid. Likewise, data from the " information grid " (i.e., the Internet) is cached in device-local storage (memory, flash memory, disk, etc.) for use by the applications running on that device. Periodically, a device's batteries must be recharged by connecting with the fixed power grid. Performing such recharging is easy: the device can be plugged into any electrical outlet that is available; the charge can be interrupted at any time —-the longer it is plugged in, the better the charge gets, until it is fully charged; and most important, the process happens with minimal intervention by the user. Data recharging is a service that aims to provide the analogous functionality for recharging the device-resident data cache. As with battery recharging, the goal is for data recharging to function in a flexible and geographically independent manner. That is, mobile devices should be able to efficiently recharge their data by connecting at any point in the global Internet, using whatever bandwidth is available at that point, connecting for whatever amount of time they can spare, and doing so with little or no help from the user. While the analogy between recharging power and recharging data is an appealing one, obviously it can only be taken so far. A key place where the analogy breaks down is that while electrons are basically fungible, the data needed on a particular device is highly dependent on the user of that device and the tasks they will be performing when they need the data. Thus, the choice of data that must be sent to a device in order to recharge it is dependent on the semantics of the applications. The data recharging infrastructure must therefore maintain and exploit information about the data needs of users. The key technology used for …