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1 - Call for pizza and
get the service details,
such as available
pizzas, toppings, etc.
2 - Place request with
the pizza details and
delivery location.
3 - Prepare and
deliver pizza to the
Pizza Requester
Pizza Provider
Web Service
Web Service
2-SOAP Request
3-SOAP Response
Figure 11-1
Simple Web services comparison with a real-world
pizza service.
As with the pizza service, where the customer must provide
required information such as type of pizza, toppings, and delivery
location, a Web service requester also must provide required inputs
for an operation to the provider so that it can process the requested
service. Web services use the Simple Object Access Protocol (SOAP)
standard for exchanging the XML messages between requester and
provider. (SOAP is the industry accepted XML messaging standard
for Web services; for details refer to [Haefel 2003].) The Web service
requester sends a message using the SOAP protocol and the provider
processes the request and responds with the appropriate SOAP
response message as defined in the WSDL document. Because the
requester has the provider's WSDL document, it knows what to
expect for a response and the semantics of the response message for
the specific request.
In the pizza service example, we assumed that the customer
already knows the contact details of Eat Fat Pizza . If the customer
doesn't know the local pizza services, then he typically searches in
the yellow pages to find the list of pizza providers and selects one
from which to order the pizza. Similarly, in the case of a Web service,
the provider can also publish its services by registering the WSDL
documents in Web service registries.
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