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Strategies to build SOAP-based web services
As we have just discussed, the service description is provided by a commonly used docu-
ment interface named WSDL that exposes the services as a collection of networks, end-
points, and ports, using the XML format.
You may logically be inclined to think that it is necessary to state the corresponding pro-
gramming interfaces at the beginning of the contract of a service and then produce them.
Actually, you can follow two approaches to develop your SOAP web services:
Top-down : This development strategy involves creating a web service from a
WSDL file. The top-down approach is likely to be used when creating web ser-
vices from scratch. It is the preferred choice of pure web service engineers because
it is business-driven, that is, the contract is defined by business people and so the
software is designed to fit the web service contract.
Bottom-up : This approach requires the WSDL file to be generated by the pro-
gramming interfaces. It is likely to be used when we have existing applications that
we want to expose as web services. As this approach does not require a deep
knowledge of the WSDL syntax, it is the easiest choice if you want to turn your
Java classes or EJB into web services.
As the audience of this topic is composed mainly of Java developers with little or no know-
ledge of WSDL basics, we will focus primarily on the bottom-up approach.
Designing top-down web services, on the other hand, will require you to integrate the basic
web services notions provided with this chapter with a comprehensive awareness of the
WSDL standard.
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