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amrameshreddy.blog.com22 CHAPTER 1 ■ INTRODUCING SERVICE-ORIENTED ARCHITECTUREramrameshreddy.blog.com• UDDI makes it possible to discover the right service that can be used, instead of reinventingthe wheel.• UDDI solves the customer-driven need to remove barriers to allow for the rapid participationin the global Internet economy.• UDDI describes services and business processes programmatically in a single, open,and secure environment.■Note UDDI offers more than design-time support. It plays a critical role after the discovery of a servicebecause it allows the client to programmatically query the UDDI infrastructure, which further allows theclient applications to be more robust. With a runtime layer between the client and the web service, theclients can be loosely coupled, allowing them to be more flexible to the changes. Microsoft recommendspublishing a WS-MEX as part of the entries in the UDDI registry.Now you are familiar with SOAP, WSDL, and UDDI. However, how do all these technologieswork together to send a message from the sender to the receiver in a loosely coupledsystem? You’ll now investigate how to achieve this.Sending Messages Between Loosely CoupledSystemsTo achieve service orientation, you need the ability to send messages from one service toanother. In the context of WCF, service invocation is a general mechanism for sending messagesbetween an entity that requests a service and another entity that provides the service. Itis important to understand that it does not matter where the provider and consumer physicallyexist; they could be on the same physical machine or spread across the opposite ends ofthe planet. However, from a service execution perspective, it matters, and WCF fills this infrastructuregap.Service invocation, irrespective of platform and technology, follows a similar pattern. At ahigh level, the steps involved when a consumer sends a message to a provider are as follows:1. Find the relevant service that exposes the desired functionality.2. Find out the type and format of the messages that the service would accept.3. Understand any specific metadata that might be required as part of the message (forexample, for transaction or security).ramrameshreddyramrameshreddy4. Send the message to the provider with all relevant data and metadata.5. Process the response message from the service in the appropriate manner (for example,the request might have been successful, or it might have failed because ofincorrect data or network failure, and so on).