Web Services for Synchronous Integration

A Web service is an abstract entity that defines a piece of functionality. It is particularly powerful due to this abstraction, as the business entity may be implemented with any technology. Commonly, Web services are seen as being built on .NET or Java EE, but there is nothing to stop someone building them in any technology, and there are toolkits available for other languages such as PHP and Perl.

When a Web service is deployed, it is defined using a WSDL (Web Services Description Language) document. This document, built in XML, is machine-readable and allows for processes to infer how to talk to a Web service and how to interpret the data that is returned. The typical scenario is that a developer uses a tool to generate a Web services proxy from the WSDL code and then implements functionality to talk to the Web service using this proxy. As such, integration is quick and simple. The consuming application calls this proxy, and the proxy is a standard, automatically generated class.

Unfortunately, this process isn't always as simple as it should be. Different software vendors have implemented how this WSDL should work in slightly different ways, which has led to the interoperability challenges that this book will help the reader surmount. In addition, the Web Services Interoperability (WSI) organization (www.ws-i.org) has been formed to define and scope out the interoperability challenges that implementers face. They define a sample application that branches multiple enterprises and multiple technologies, interoperating via Web services. This application, called Supply Chain Management, is used throughout this book to demonstrate the various interoperability technologies and techniques. By stepping through this application and its data requirements and by using both .NET and Java EE technologies, a good understanding can be gainednot only of the methodologies that may be used for system integration using Web services, but also how to build a system using these technologies.