Mobile technology is technology that is portable. Examples of the mobile devices are mobile phone, PDA and others. Mobile devices can use Wireless Internet Access to search the web content anytime and anyplace from the mobile.
Web service is recognize by Uniform Resource Identifier (URI) and using Extensible Markup Language (XML) to define and described the public interface of web services. With using XML, it can solve the enterprise integration problems. Besides that, web services require using the several related XML-based technologies such as Web Services Description Language (WSDL), Simple Object Access Protocol (SOAP) and Universal Description, Discovery, and Integration (UDDI).
A mobile web service is combining the mobile technology with the web services. With the mobile web services, information such as entertainment, news, weather forecasting, traffic and so on can get it easily.
(M. Tian, 2003)
Discussion
Mobile Web Service
A mobile web service is applying Service-Oriented Architecture to the mobile environment.
Service-Oriented Architecture (SOA) is an approach of building and designing distributed systems.SOA deliver the services to the end-user application or to other services which are distributed in the network. (Satish Narayana Srirama, 2006)
SOA defines three interaction roles which are service provider, service registry and service requestor/client. Figure 2.1 show the SOA operation. The basic operation publish, find, bind and description of SOA are show in the Figure 2.1. (Satish Narayana Srirama, 2006)
Figure 2.1 Operation of SOA. (Satish Narayana Srirama, 2006)
The web services architecture enable application to application communication through the network. Web services are self-contained business task, a full-fledged business process, an applications or a services-enabled resource whose public interfaces are described using WSDL. Web services using standard web technologies and protocols like SOAP and HTTP for access to the software components. A service provider develops and deploys the service and publishes its description and binding/access details (WSDL) with the UDDI registry. To get the service description, the client queries the UDDI. Then access the service with using SOAP. The communication between client and UDDI registry is also based on SOAP. (Satish Narayana Srirama, 2006)
The quest for enabling these open XML web service interfaces and standardized protocols also on the radio link lead to new domain of applications mobile web services. In this domain, the resource constrained mobile devices are used as both web service clients and providers. (Satish Narayana Srirama, 2006)
Nowadays, standard web service technologies can be applied to several mobile devices almost without any problems. But standard web service protocols have several drawbacks. For example, the textual representation of XML-based descriptions as used in WSDL and SOAP leads to a low information density and thus to an inefficient use of communication bandwidth. The synchronicity of HTTP results in intolerance to network failures and excludes typical mobile network technologies such as Bluetooth or IrDA. Concerning the discovery of mobile services, centralized systems such as UDDI can hardly be applied in decentralized networks and prove to be inefficient in systems with changing network addresses (S. Zaplata et. al., 2009)
Alternative Technologies
Sometimes the standard web services protocol cannot adequately meet the needs of resource-restricted mobile computing infrastructures such as XML in service descriptions and messages, the synchronicity of communication and the centralization of registry information. Therefore, alternative technologies have evolved.
The following are the list of example of alternative technologies:
Use alternative description languages to instead XML to reduce complexity in another way such as such as JavaScript Object Notation (JSON) or Abstract Syntax Notation Number One (ASN.1).
For appropriate asynchronous communication, using alternative protocols such as Standard Mail Transfer Protocol (SMTP) and Post Office Protocol (POP)/Internet Message Protocol (IMAP) for decoupling sender and receiver and thus allowing disconnected operation of web services.
Performing message exchange over Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) directly to eliminate the overhead of HTTP.
To minimize the size of XML messages, Universal (e.g. ZIP) or XML-specific (e.g.
XMILL) compression mechanisms can efficiently be used.
(S. Zaplata et. al., 2009)
Publishing and Discovery of Mobile Web Services
Typically, web services are developing for the network and publish to the UDDI. Any potential client searches for the web service in the UDDI, gets the WSDL of the service and then accesses the web service using the information specified by the WSDL document. The numerous web services possible with each mobile phone user providing some services in the mobile operator network may make the centralized UDDI registry not the best solution. (Satish Narayana Srirama, 2006)
Besides, mobile networks are dynamic due to node movement. Nodes can join or leave network at any time and can switch from one operator to another operator through the network. This might make the binding information in the WSDL documents, inappropriate. Keeping up to date information of the published services in central registries is really difficult. JXTA can provide alternatives for these problems. (Satish Narayana Srirama, 2006)
JXTA (Juxtapose) is an open source peer-to-peer (P2P) protocol specification and develop by Sun Microsystems in 2001. JXTA peers use XML as standard message format and create a virtual P2P network over these devices connected over different networks. JXTA can scale by collaboratively using the resources of individual peers. Module advertisements provide alternatives for mobile web service discovery. (Satish Narayana Srirama, 2006)
From the technical perspective, the mobile host should be realized in JXTA network and the final deployment scenario is to be reached. The approach provides alternative addressing mechanisms for mobile host. (Satish Narayana Srirama, 2006)
Conclusion
Web services have a lot of service distributions and mobile phones have large user base. Therefore, combining web services with the mobile technology will brings us a new trend.
On the other hand, mobile web services will also lead to manifold opportunities to mobile operators, wireless equipment vendors, third-party application developers, and end users.
