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SOAP - CHAPTER 14 SOAP Web Services F ormerly considered a...

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393 C H A P T E R 1 4 SOAP Web Services F ormerly considered a buzzword, Service-Oriented Architecture (SOA) today forms part of day-to-day architectural life. However, sometimes it is confused with web services. SOA is an architecture principally based upon service-oriented applications that can be implemented with different technologies such as web services. Web services are said to be “loosely coupled” because the client of a web service doesn’t have to know its implementation details (such as the language used to develop it or the method signature). The consumer is able to invoke a web service using a self-explanatory interface describing the available business methods (parameters and return value). The underlying implementation can be done in any language (Visual Basic, C#, C, C++, Java, etc.). A consumer and a service will still be able to exchange data in a loosely coupled way: using XML documents. A consumer sends a request to a web service in the form of an XML docu- ment, and, optionally, receives a reply, also in XML. Web services are also about distribution. Distributed software has been around for a long time, but unlike existing distributed systems, web services are adapted to the Web. The default network protocol is HTTP, a well-known and robust stateless protocol. Web services are everywhere, and they can run on desktops or be used for business-to- business (B2B) integration so that operations that previously required manual intervention are performed automatically. Web services integrate applications run by various organizations through the Internet or within the same company (which is known as Enterprise Application Integration, or EAI). In all cases, web services provide a standard way to connect diverse pieces of software. Understanding Web Services Simply put, web services constitute a kind of business logic exposed via a service interface to a client application (i.e., a service consumer). However, unlike objects or EJBs, web services pro- vide a loosely coupled interface using XML. Web service standards specify that the interface to which a message is sent should define the format of the message request and response, and mechanisms to publish and to discover web service interfaces (a registry). In the Figure 14-1, you can see a high-level picture of a web service interaction. The web service can optionally register its interface into a registry (UDDI) so a consumer can discover it. Once the consumer knows the interface of the service and the message format, it can send a request and receive a response.
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CHAPTER 14 SOAP WEB SERVICES 394 Figure 14-1. The consumer discovers the service through a registry. Web services require several technologies and protocols to transport and to transform data from a consumer to a service in a standard way. The ones that you will come across more often are the following: s 5NIVERSAL $ESCRIPTION $ISCOVERY, AND )NTEGRATION (5$$)* IS A REGISTRY AND DISCOVERY mechanism, similar to the Yellow Pages, that is used for storing and categorizing web services interfaces.
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