Applications for Mobile Information Devices

Commands To ensure application portability across devices, a method is needed to insulate the developer from the actual set of buttons that may be on a device (button sets will vary significantly among devices). As mentioned earlier, MIDs will either have a one-handed ITU-T phone keypad or a two-handed QWERTY-style keyboard. Beyond that, devices may have any number of programmable (soft) buttons or no programmable buttons at all. There may be dedicated hardware buttons for Back, Help, Clear, etc., or there may no dedicated buttons at all. The Abstract command API is the layer that is used to map between the buttons on a device and the set of commands that an application developer attaches to a screen. This ultimate mapping of commands onto the device is a prerogative of the manufacturer. Developers gain the freedom of creating portable applications, but lose control over where each specific command will map on the device. However, the policy for how buttons are mapped on a particular device is the same for all applications that run on that device. In other words, there is one policy per phone. What is possible is to define the set of actions the user can select from each screen in the particular application. Each action is defined as a command with an associated command type, priority, and label. The type, priority, and label provide hints to the underlying device implementation that can be used to map the commands appropriately. For example, a command of type HELP might get mapped to a dedicated Help button on a phone. When specifying the commands associated with a screen, based on the command type, priority, and label, the underlying implementation uses the abstract command APIs to determine where on the physical device those commands will be mapped. On some devices the commands may be mapped to programmable buttons that may or may not have a label associated with them. Other devices may use roller buttons, joysticks, or instead of buttons, a menu-style user interface.