【正文】 AND W EB SERVICES A. Wireless LAN A wireless LAN (WLAN, Wireless Local Area Network) is a flexible data munication system implemented as an extension to or as an alternative for, a wired LAN within a building or campus . Using electromagic waves, WLANs transmit and receive data over the air, minimizing the need for wired connections. Thus, WLANs bine data connectivity with user mobility, and, through simplified configuration, enable movable LANs. The IEEE group of standards specifies the technologies for wireless LANs. 2 standards use the Ether protocol and CSMA/CA (carrier sense multiple access with collision avoidance) for path sharing and include an encryption method, the Wired Equivalent Privacy algorithm. The , b, and g standards are the most mon for home wireless access points and large business wireless systems. A remote user can use WLAN to access the Inter through public access points (“hotspots”) provided by service providers. When in the office, they may access WLAN through wireless access points. In enterprise environments, WLANs are usually plemented by security mechanisms, such as VPN (Virtual Private Network). Over the last several years, WLANs have gained strong popularity in some markets, including the healthcare, retail, manufacturing, and academic areas. These industries have profited from the productivity gains of using handheld terminals and notebook puters to transmit realtime information to centralized hosts for processing. Today WLANs are being more widely recognized as a generalpurpose connectivity alternative for a broad range of business customers. B. Web Services Quickly being a significant technology in the evolution of the Inter is web services, a set of standards that can interconnect systems over a verity of works. It is an open XMLbased technology providing a generic data exchange format and has been rapidly adopted by many vendors. Web services can easily be built upon existing applications, no matter what the underlying technology is. Because they are expected to have a growing familiarity and acceptance among many users and offer great technological promises, Web services are an interesting subject for the investigation of their possible application in many systems . Web services are a new generation of web application. It bines the advantages of the ponentoriented methods and web techniques, and they can describe its own service. It can also publish, locate and transfer modularized application in web. The provided functions of web services may be simple, but it also contains extraordinary plicated business logic. Web services represent a kind of implementation of SOA (ServiceOriented Architecture), and they are the most popular one. In addition, the three operations of SOA can only process when the ponents of SOA interact. Therefore some standardized techniques are used in web services, including UDDI, WSDL, HTTP, SOAP, and XML and so on. Web services bee the best choice for developing application of SOA . III. DESIGN AND I MPLEMENTATION OF THE SYSTEM A. System Architecture In the system, we adopt fourtiered webbased clientserver architecture. Figure 1 shows the overview of the system architecture. The system is conceptually posed of six main ponents: the web server, database server, cash register, mobile context server, mobile user and desktop user. The web server provided relevant information for mobile devices or desktop PCs on a wired/wireless integrated local area work using WSDL (Web Service Description Language) to describe functions and protocols. The web server then transmits to the mobile devices or desktop PCs. The user binds the web server and the WSDL. This enables the web service to be used by correspondence using SOAP (Simple Object Access Protocol). The database server saves all information of the system such as food information, ordering information, client information. The cash register is responsible for cost calculation of the consumer. The mobile context server applies context to the contents by using styles, an attribute override, and templates according to the resources of a given mobile device. Desktop users can ask for services after checking the WSDL of the service from the web 3 server. A desktop on a wired work can be used to browse full contents on one screen shot. When a user requests food information through a wired work, the web server serves the information by connecting to the database server. When a user requests food infor mation through a wireless work, the mobile context server divides the context pages according to the screen size of the mobile device. It also filters the pages according to mobile devices and then browses the adopted content from the context server to the mobile web browser. The mobile context server reconfigures contents offered by the web server. Figure 1 The System Architecture B. Web Service Security Model Web service security can be applied at three levels : ? Platform/transportlevel (pointtopoint) security。 ? Messagelevel (endtoend) security. Each approach has different strengths and weaknesses. The choice of the approach is largely dependent on the characteristics of the architecture and platforms involved in the message exchange. This system focuses on platform and applicationlevel security, so the two security levels are described. (pointtopoint) security The transport channel between two endpoints (web service client and web service) can be used to provide pointtopoint security as illustrated in Figure 2. Figure 2 Platform/transportlevel security In the platformlevel model, the client sends an XML format request to the web server. The XML message is not encrypted by the client. When the message is transported in the transport 4 channel, the work encrypts the entire data stream to make sure that the transport is secure. This system uses a tightly coupled Microsoft Windows ope