XML Web services infrastructure

Abstract msdn.
To succeed in the world of Web diversity, XML Web services cannot have any preference when it comes to the selection of operating systems, object models, and programming languages. Similarly, to make XML Web services widely used like other Web-based technologies, they must be:
Loose coupling: if the only requirement on the two systems is to understand the self-described text-based messages mentioned above, the two systems are considered loose coupling. On the other hand, tightly coupled systems require a large amount of custom system overhead for communication, and require more understanding between systems.
Common communication: no one may generate an operating system that cannot connect to the Internet in the present or near future. Therefore, a common communication channel is required. Similarly, the ability to connect almost all systems or devices to the Internet will ensure that such systems and devices can be used by all other systems or devices connected to the Internet.
General data format: by using existing open standards instead of dedicated closed communication methods, any system that supports the same open standards can understand XML Web services. When self-describing text-based messages are used, XML Web services and its clients can share the message without having to know the composition of each basic system, this enables communication between autonomous systems and completely different systems. XML Web services uses XML to implement this function.
XML Web services adopts a basic structure that provides the following content: locate the XML Web services discovery mechanism, define the service description for using these services, and use the standard connection form for communication. The following figure shows an example of the basic structure.
XML Web services infrastructure
The XML Web services directory provides a central location for locating XML Web services provided by other units. The XML Web services Directory (such as the UDDI registry) acts as this role. The XML Web services client may or may not need to reference the directory of XML Web services.
XML Web services discovery is a process of locating (or discovering) one or more relevant documents that use the Web service description Language (WSDL) to describe specific XML Web services. The DISCO specification defines the algorithm for locating the service description. If the XML Web services client knows the location of the service description, they can skip the discovery process.