Smart Mobile devices and web services are becoming very popular. Mobile devices are physically constrained devices; low processor speed, limited memory, limited battery, and slow intermit wireless connection. This implies to take in consideration these factors when implementing web services for mobile devices. In this paper, we evaluate the RESTful web service for mobile devices against conventional SOAP web services. The experimental results show that RESTful web services outperform conventional SOAP web services. A recommendation to use RESTful web services on mobile devices has been concluded from experimental result.
Like its predecessors, such as the Common Request Broker Architecture (CORBA), Remote Method Invocation (RMI) and Distributed Component Object Model (DCOM), Web Services  is a set of standards and a programming methods for sharing data between different software applications, moreover Web services is a standardized way to distribute services on the Internet.
Web Services achieves its goal in a technologyneutral manner; it provides well-defined interfaces for distributed functionalities, which are independent of the hardware platform, the operating system, and the programming language. So distributed functionalities, or services, which may be running on different hardware platforms, may be running in different operating systems, or may be written in different programming languages, can communicate through web Service interfaces.
Interoperability of Web Services mainly stems from its Extensible Markup Language (XML) based open standards. The Simple Object Access Protocol (SOAP)  is defined in XML. Since it is text-based and selfdescribing, SOAP messages can convey information between services in heterogeneous computing environments without worrying about conversion problems, there are many other Web Service specifications. Two of them, which are based on XML, are Web Service Description Language (WSDL)  and Universal Description, Discovery and Integration (UDDI) . WSDL defines a standard method of describing a Web Service and its capability, and UDDI defines XML-based-rules for publishing Web Service information. Messages are exchanged through the SOAP protocol. SOAP works by exchanging information using GET/POST over HTTP. This allows the data to be exchanged regardless of where the client is in the network.
Just as Web Services technology has become an industry standard for connecting remote and heterogeneous resources, mobile devices have become a vital part of people’s everyday life. People use mobile devices anytime and anywhere, they may use their mobiles to check Email, access the Internet, or run other web applications.
Web Services technology recognizes mobile computing as an area to which it should expand. Through integration, Web Services enable pervasive accessibility by allowing for user mobility as it overcomes the physical location constraints of conventional computing. However, mobile computing also requires a technology that connects mobile systems to a conventional distributed computing environment. Web Services may be the perfect candidate for such connection, since a strong interoperable capability is the key requirement of the technology. This will be important for its success when we consider the fact that the mobile computing environment is much heterogeneous in terms of hardware platform, operating system, and programming language. Thus, the integration of mobile computing with Web Services technology will give many advantages to both sides. Mobile devices getting computationally capable, so mobile devices enabled with web services can be equal participant of web services architectures (can be web service client or web service provider).
However, despite the fact that the condition of mobile computing has so much improved in recent years , applying current Web Service communication models to mobile computing may result in unacceptable performance overheads. This potential problem comes from two factors. First, the encoding and decoding of verbose XML-based SOAP messages consumes resources. Therefore Web Service participants, particularly mobile clients, may suffer from poor performance. Second, the performance and quality gap between wireless and wired communication will not close quickly. It is caused by the mobile environment’s constraints like limited processor speed, limited battery lifetime, and slow unreliable and intermit connection.
Mobile web services is an open research area [2, 3, 5, 13, 22, 27]. Several messaging optimization approaches have been introduced to the literature [20, 26, 15, 16, 17, 18, 19, 25] to address web service performance overhead for mobile devices. As described previously, applying current Web Service communication models to mobile computing may result in unacceptable performance overheads. The typical web application that requires the transmission of four to five times more bytes if implemented as a Web service compared to the same service implemented as a traditional dynamic program (e.g. Active Server Page application)  (more details in state-of-art section).