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Web Service is an application programming interface (API) or Web API that is accessed using Hypertext Transfer Protocol (HTTP) and then implemented on another remote system, hosting the requested service. Web service is both a process and set of protocols for searching and connecting to the software that exhibits a service over the web. Web service has 4 basic platform elements: i) XML ii) SOAP iii) WSDL iv) UDDI. (Wikipedia, 2010)
Throughout the years, the Internet now can be seen as a large-scale distributed information system with a lot of information and also providers. A few trends emerged as influenced and one of the major trends is the shift of stationary to mobile distributed information management. According to Krishnan (n.d.) mobile phone population is expected to reach 4 billions by the end of year 2010. From the current world population of over 6 billions, 2 per 3rd population are having a mobile phone. This means out of 3 people, 2 persons are having their own mobile phone.
With the high usage of mobile phones all around the globe, companies are trying to make this an advantage for their business. Mobile devices are now being turned into wireless Web Service clients, this will lead to more open opportunities to mobile operators, wireless equipment vendors, 3rd-party application developers and also end users. It would be nice for programs in mobile devices to act as both service requester and also service provider. When programs on a device interact automatically with another program on another device, it requires less attention from the user.
With web service on mobile devices, one can get a lot of benefits. For example, people carry credit cards, identification cards, etc. these physical items in their daily lives, it would be nice if they are provisioned as web service on a mobile device. User can just carry their mobile device and make transaction as the services can provide the information such as credit card number for making the transaction. There are many other possibilities by combining several simple web services to build more useful services. These combinations could provide a set of more flexible services for users to get real time information from the Internet
Architecture of Mobile Web Service Provider
There are 3 main components of a basic web service: Service Provider (Host), Service Requester (Client) and Service Registry. In Figure 1, a smart phone acts as the web service provider. The service provider publish its web service with the service registry while the client find the UDDI registry for the service. The UDDI compatible service registry will refer the WSDL describing the web service. Finally the client is able to bind and access the web service using SOAP.
Figure 1. Basic architectural setup of Mobile Host (Srirama et al, 2006)
The Mobile Host has been developed as a web service handler built on top of a normal web server. In Figure 2, it shows the core architecture of the mobile host. When mobile host gets a request, the server socket in the HTP interface will accepts it and then creates a socket for communication, and initiates a new thread of execution by creating an instance of the request handler. The request handler will then check the web service requests sent via HTTP tunneling. If the request is a normal HTTP request, the request handler will process the request as standard web server, returning response by writing to the output stream of the socket.
If the request consist a web service request, the request handler will read the HTTP and de-serialize the SOAP request into JAVA objects, using the SOAP Processor. The objects are then passed to the service handler to extract and then invoke the service. After the service method is executed, the service handler will then return the response to the request handler.
Figure 2. Core architecture of Mobile Host
Traditionally, mobile system is designed as client-server systems. Mobile devices such as PDAs use wireless connection to get information of resources provided by central servers. The fresh approach is to design mobile system using peer-to-peer architecture, but this approach still requires more research.
The key challenges in this approach are:
To keep the Mobile Host compatible with the usual Web Service so the end user will not notice the difference
To design a very small sized footprint Mobile Host.
To limit the performance of the web service functionality
For mobile devices, it has lower CPU power, smaller memory and storage capacities comparing to desktop computers and servers. So web service implementation on mobile service must be within the minimal usage on computation, memory and energy resources.