WSDL (Web Services Description Language) is an XML vocabulary that lets developers describe Web services and their capabilities in a standardised format. A typical WSDL schema is as shown in the Figure 16-3 below.
Figure 16-3. WSDL schema
The node <definitions> is the root node of WSDL. For allow other entities for including use the <import> node. For defining data definitions use the <types> node. To define the parameters of a web service function use the <message> node. To define input and output operations use the <prototype> node. Finally, to specify how each message to be send over the wire, use <binding> node.
UDDI (Universal Description, Discovery and Integration) is a framework that defines XML-based registries where businesses can publish information about themselves and the web services they offer that other businesses can access and use. The UDDI information model is as shown in Figure 16-4.
Figure 16-4. UDDI information model
Note: In Figure 16-4, the bindings contain references to tModels. These references designate the interface specifications for the exposed services.
Web Service Architecture
The Web services architecture is based upon the interactions between three primary roles, namely service provider, service registry, and service requestor. These roles interact with each other using publish, find, and bind operations. Figure 16-5 shows a typical web service architecture which shows the primary roles and the interaction mechanisms.
Figure 16-5. Web service architecture
The major roles played within the web service architecture are as detailed below:
- Service Provider – provider of the actual web service exposed. Service provider implements the service and makes it available on the Internet for other to consume and use.
- Service Requestor – any consumer of the web service. Requestor utilizes an existing web service by opening a network connection and sending an XML request.
- Service Registry – centralized directory of services. The registry provides a central place where developers/enterprises can publish new services or find existing ones.
Overall in the web service architecture, the interaction between various roles can be explained as follows: The service provider is the business that provides access to the Web service and publishes the service description in a service registry. The service requestor finds the service description in a service registry and uses the information in the description to bind to a service.
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