11.1 Database on the Go One of the biggest obstacles of WAP-based mobile commerce is the requirement of uninterrupted wireless network coverage. Today's unreliable and incomplete wireless network infrastructure leaves the anywhere, anytime promise of mobile commerce unfulfilled. Fortunately, the widespread adoption of the smart mobile client technology will change this picture and enable new generations of mobile applications. A key benefit of smart clients is that they can function in the offline mode when the wireless network connection is temporarily unavailable. The offline mode drastically improves the application availability. In fact, most of today's mobile applications primarily work in the offline mode. Users carry their PDAs or barcode scanners all day. They synchronize data with desktop computers only once or twice a day. The disconnected mobile application architecture is a proven success. To support offline operations, the mobile client must store application data locally. There are great needs for first-class data management tools on mobile devices. Lightweight relational databases are just the tools we are looking for. Compared with linear data storage facilities (e.g., plain file or the MIDP RMS) that come with J2ME standard profiles, relational databases are much more efficient for complex data. Besides supporting highly available…

10.1 Mobile Enterprise Messaging  More examples on the RPC scheme . Although RPC style integration is simple and does not require any middleware, it is sometimes not optimal in the occasionally connected, unreliable, and heterogeneous mobile environments. Error handling and quality-of-service (QoS)-level guarantees are difficult to implement in RPC environments. The messaging scheme, however, offers great advantages in some key enterprise areas. The benefits of enterprise messaging are as follows. Universal integration: In the messaging scheme, the message sender and receiver are completely decoupled. They interact only with standard interfaces defined by the messaging protocol and do not need to know the status or availability of the other party. This allows automatic and seamless integration between enterprise components. For mobile applications that run on many different devices and use different network transport protocols, messaging-based integration is crucial. Reliability: Due to the intermittent nature of wireless networks, communication reliability is a big concern for mission-critical mobile applications. In a messaging application, we can guarantee message delivery or at least notify the sender when the delivery is failed or not completed after a certain amount of time. Scalability: In an asynchronous messaging solution, the server resource is not tied up by idle…

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7.1 Limited Device Hardware The most visible difference between the mobile and PC platforms is the difference in computing hardware. Today's PCs have much faster CPUs and far more memory and storage spaces than any mobile computing devices. Desktop and server developers can afford the luxury to write applications with bloated features (e.g., Microsoft Office); they also have access to rich productivity features provided by large, all-in-one frameworks (such as the J2SE platform itself). However, on mobile devices, it is a completely different story. With CPUs as slow as 20MHz and RAM as little as 100KB, we must carefully evaluate the features we need, thoroughly optimize our code, and live with limited framework support. In this section, we discuss how to cope with those challenges. 7.1.1 Lightweight Libraries The most common mistake beginners make is the "golden hammer" anti-pattern: choosing the wrong technology for the task. In the Java world, software tools are often available as reusable objects in standard or third-party libraries. To choose the best libraries that support required application features at the minimum hardware cost is essential. J2ME Foundation and Personal Profiles (as well as PersonalJava) are compatible with J2SE at the bytecode level and inherit a…