Introducing SOAP, WSDL, and UDDI

reference:

http://h71000.www7.hp.com/openvms/journal/v4/examining_web_services.html

There are three standards-based technologies that, along with XML, comprise the core of web services.

• SOAP (Simple Object Access Protocol)
  The function of SOAP is to transmit XML messages between two applications. SOAP is itself an XML language and is defined using an XML schema.

• WSDL (Web Services Description Language)
  WSDL is a language based on XML. It is used to precisely define the details of a web service. Web service consumers use this information to build SOAP messages for the service the WSDL describes.

• UDDI (Universal Description, Discover, and Integration)

• UDDI is a specification that defines a directory for web services. Often called the "Yellow Pages for Web Services," UDDI directories are used to store services that are available to consumers.

Figure 5 provides a high-level overview of how the SOAP, WSDL, and UDDI technologies interact. These three technologies were defined specifically for use with web services. In Figure 5, a web services client performs the following steps to obtain a stock quote from an OpenVMS application that has been exposed as a web service.

Step 1:  The client looks in a UDDI directory to find a web service that can supply stock quotes. It discovers the stockQuote service can supply the desired features. The UDDI registry provides an address, in the form of a URL, to the client. (You can skip this step if the client already knows the address of the web service.)

Step 2:  The client sends a lookup request to the address obtained in step1, asking for a description of the service. This description is returned to the client in an XML schema language called WSDL.

Step 3:  The consumer uses the WSDL description obtained in step 2 to identify the details of the service's functions and associated arguments. The client makes a call to the stockQuote service by sending a SOAP protocol request.

Step 4:  The web services platform receives the SOAP protocol request and returns the quote to the client via a SOAP protocol response.