Next Generation Wireless Applications: Creating Mobile Applications in a Web 2.0 and Mobile 2.0 World, 2nd Edition

10.4 SERVICE LAYER

The service layer is the ‘business logic’ of our mobile device application. A mobile service in its entirety can involve many interlocking functions, services and software spread across the entire mobile network. There are three modes of implementation:

1. Client–server (CS)
2. Peer-to-peer (P2P)
3. Standalone

These are purely modes of implementation, mostly reflecting the mode of collaboration with other software services in the network; they are not categories of application. For example, a particular application, such as a calendar tool, may well be able to operate in all three modes of operation depending on the context of use.

A user may wish to consult with their calendar, just to read appointments, survey the coming day's events, etc. This would seem not to require access to other services in the network, which makes it a standalone application. However, even this apparently innocuous requirement requires a lot of processing on the device, so we should not think of it as a trivial task just because we are not involving any networked activity at this stage.

For a moment, let's pause to consider what the processing requirements might be:

• Accessing a particular area of memory to read calendar values
• Processing the calendar values to transform them from an internal digital representation to a human readable one
• Creating a whole set of display widgets to display a calendar on the screen
• Rendering the graphics widgets on the LCD display, pixel by pixel
• Reacting to ...