Java Reference
In-Depth Information
JDM vendors can enable JDMWS using the JDM API and J2EE
platform.
11.1
What Is a Web Service?
There are many industry definitions for Web services. The latest W3C
Web Services Architecture document defines a Web service as follows:
A Web service is a software system designed to support interoperable machine-to-
machine interaction over a network. It has an interface described in a machine-
processable format (specifically WSDL). Other systems interact with the Web service
in a manner prescribed by its description using SOAP-messages, typically conveyed
using HTTP with an XML serialization in conjunction with other Web-related
standards. [WS-ARCH 2006]
Even though this definition may be difficult to understand at first,
Web services are similar to real-world services. This section uses a
fictitious pizza service, Eat Fat Pizza in New York City, to compare
concepts and workings of Web services with those of real-world
services.
Eat Fat Pizza offers custom pizzas to customers by delivery or
pickup. It offers two delivery options: deliver by bike to avoid delays
due to city traffic or by car if the customer is not within two miles of
its location. Typically, customers make a phone call and inquire about
the types of pizzas available, and then order the pizza, specifying
toppings, drinks, etc. In response to a customer request, the Eat Fat
Pizza service provider prepares and delivers the pizza according to
the request. Eat Fat Pizza publishes its services in the local yellow
pages, flyers, and advertisements.
Figure 11-1 illustrates the similarities between the workings of a
pizza service and the workings of a Web service. When a customer
calls, the pizza service provider gives the details of the services they
offer. Similarly, in the case of a Web service, the provider gives the
details of the services they offer using a machine interpretable XML
document to the service requester. This XML document is written
using the Web Service Description Language (WSDL, often pro-
nounced as “Whiz-Dull”). WSDL describes the types of XML ele-
ments used and the contents of the service request and response
messages, available service operations, message format, and service
provider location details. After processing the provider's WSDL doc-
ument, the requester knows which services are provided, and how to
place a request to the provider.
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