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Mobile Web Services: A New Agent-Based Framework

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Author: WildC@rd

Although mobile devices tend to share certain functionalities, they run on many different platforms, which means their development environments vary widely. As a result, users often run into integration problems when attempting to access desktop applications via mobile devices. Could Web services provide an answer? Web services can act as mobile clients, independent of a given mobile device’s operating system or the client’s application. We can use one of three architectures to implement a mobile Web service, as they’re usually known in the mobile domain: a wireless portal network, the wireless extended Internet, or a peer-to-peer (P2P) network.1 A wireless portal network has a gateway between the mobile client and the Web service provider; this gateway takes care of all SOAP/HTTP requests and returns responses in a supported format. In a wireless extended Internet architecture, mobile clients interact directly with Web service providers; they’re true Web services clients and can send or receive SOAP messages.1 In a P2P network, mobile devices can also act as Web service providers in addition to requesting Web services, which is especially beneficial in ad hoc networks. In this article, we’ll describe our agent-based mobile services framework. It uses wireless portal networks and eliminates XML processing on mobile clients. It also offers dynamic service selection and rapid application development and deployment for Web service providers. The technology The overhead involved in XML processing presents a huge problem for mobile Web services applications. Many researchers have experimented with performance improvements such as faster parsers,2 data compression,3 protocol optimizations,4 or binary encodings,5 but the outcome generally depends on the structure of the data used and the application itself. Another important issue that influences performance is the choice of architecture—a wireless portal network architecture, for example, avoids XML processing on mobile devices, whereas a wireless extended Internet architecture requires XML processing as well as the ability to transfer SOAP messages. Moreover, in a wireless extended Internet architecture, new or updated applications must be downloaded over wireless networks before the user can use them. This process is time-consuming and costly because of the additional data that must be transferred over limited bandwidth. Let’s look more closely at the technologies that constitute these architectures. Mobile agents A mobile agent is an autonomous program that gathers information or accomplishes tasks without human interaction and can also self-migrate in a heterogeneous network.6 This means a mobile agent can suspend its execution at an arbitrary point, transfer itself to another machine, and then resume its execution from the point at which it left off. Mobile agents are deployed in handheld devices in one of two ways: on a platform that lets mobile agents run on it directly, or on devices that can access and use remote mobile agents running on wired networks.7 The first method provides local execution, which is beneficial for high-end devices, especially when the network connection is unreliable. The second method is beneficial for devices with limited processing power and memory. Web services orchestration Web services orchestration is the arrangement and management of different services to achieve a desired goal.8 Most of the time, one simple service can’t provide all the desired functionality, but a combination of more than one service can. At this point, orchestration becomes the layer that transforms service composition and coordination into long-running transactions and business processes.9 Service orchestration can be achieved through the use of languages to define flows and engines to execute these flows; in particular, the Business Process Execution Language (BPEL) has become a de facto industry standard (http://roadmap.cbdiforum. com/reports/protocols/?order=desc#comments). Dynamic Web service selection To perform a particular task via a Web service, an application selects a specific service during the development phase, perhaps by querying UDDI registries and looking for a match that complies with the desired functionality. After selecting a service, the program invokes it for as long as the program’s source code doesn’t change. Over time, however, this service might cease to be available or comply with user preferences, or its requirements might change. Dynamic Web service selection occurs at compile time or runtime according to nonfunctional attributes such as quality of service. QoS is a broad concept that encompasses several nonfunctional properties including availability, reliability, duration, price, and security protocols. Several proposed frameworks allow monitoring and dynamic selection for single or composite Web services.
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