 with the service in a standard-based way. The WSDL docu- ment describes the service's location on the Web and the functionality the service provides. Through the WSDL, a Web services client learns where a service can be accessed, what operations the service performs, the communication protocols the service supports, and the correct format for sending messages to the service. WSDL describes four critical pieces of data: Interface information describing all publicly available functions Data-type information for all message requests and message responses Binding information about the transport protocol to be used Address information for locating the specified service Using WSDL, a client can locate a Web service and invoke any of its publicly available functions. With WSDL-aware tools, you can also automate this process, enabling applications to easily integrate new services with little or no manual code. SOAP (Simple Object Access Protocol): SOAP is an XML-based protocol from the W3C for exchanging data over HTTP. It provides a simple, standards-based method for sending XML messages between applications. Web services use SOAP to send messages between a service and its client(s). Because HTTP is supported by all Web servers and browsers, SOAP messages can be sent between applications regardless of their platform or program- ming language. This quality gives Web services their characteristic interoperability. To be able to understand in an easy and elegant way how the SOAP protocol works, we will present a communications example (using SOAP) between a client and Tele-Measurement Services for m-Learning SOAP Request: "which is the temperature for the city with the ZIP code 2200?" Server SOAP Answer: Figure 12.37 SOAP example. a server. This example (shown in Figure 12.37) presents a very simple weather service, which shows the current temperature for a specified location using the ZIP code. SOAP messages are XML documents that contain some or all of the following elements: Envelope specifies that the XML document is 