Hello Indigo - What is a Service?
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This is an important question—and the answer varies depending on the context of the discussion. For example, a service is a logical term to SOA, but it has physical meaning to WCF. I’ll focus on the former in this section. According to the high-level definition of SOA, business functionality must be distributable and accessible in some way. The term service in this case refers to the entry point or “window” through which business functionality can be reached. Consider the application architecture illustrated in Figure 1-6. The client application represents an Agency Management System that includes many chunks of business functionality such as Certificate Issuance, General Ledger, CRM, and Reporting. In Figure 1-6, the client application coordinates access to these features by consuming business components directly. In this case, components are not distributable in such a way that they can be location transparent, thus they are not services.
Figure 1-6. Directly invoking business components
So, what constitutes a service in SOA terms? It could be a serviced component exposed using Enterprise Services, a .NET Remoting component, an ASMX web service, or a WCF service. Any of these technologies can be useful in exposing the business logic in such a way that the client can reach that functionality at remote locations in a distributed environment, without communicating directly with business components. Figure 1-7 illustrates the same services beneath the Agency Management System example from Figure 1-6, but this time each feature is exposed via one of the aforementioned technologies. Serviced components are reached using DCOM over TCP, .NET Remoting components via RPC over TCP, ASMX web services via SOAP over HTTP, and WCF services via SOAP over any protocol.
The point is that services are not necessarily web services—they are merely chunks of business functionality exposed in some way such that they respect the tenets of SOA.
Figure 1-7. Service boundaries implemented with different technologies
Next: Tenets of SOA >>
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 This article is excerpted from chapter 1 of the book Learning WCF A Hands-on Guide, written by Michele Leroux Bustamante (O'Reilly, 2007; ISBN: 0596101627). Check it out today at your favorite bookstore. Buy this book now.
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