A Web service describes a collection of operations that can be accessed over the Internet using standardized XML messaging. It uses protocols based on XML to describe an operation to execute or data to exchange with another Web service.
Web services use standards—groups of related protocols—to describe, deliver, and interact with other Web services. You should understand the restrictions of each standard, specifically SOAP, WSDL, and UDDI.
Simple Object Access Protocol (SOAP) – allows communication between Web services. Encodes messages so they can be delivered over the network using a transport protocol such as HTTP, IIOP, SMTP, and so on. At a basic level, SOAP is the equivalent of an empty envelope that allows you to put an electronic business document inside the SOAP envelope to create a packet that delivers an electronic message.The SOAP envelope has two parts—a header, which contains information such as an electronic address, and a body that contains the business document.
SOAP does not:
Provide address standards for what an electronic address should look like.
Provide message security or authentication to determine who sent the message.
Support long transactions. SOAP only allows you to define the way you interact with a Web service as a request or a response.
Offer reliable delivery that ensures the message was delivered.
Web Services Description Language (WSDL) – a series of XML statements that form the definition of each Web service interface. WSDL is the standard language for describing Web service interfaces. WSDL by itself only describes the pattern of communication between the parties involved and must be extended with Web service type and binding information. The type information describes exactly what must be communicated, and the binding information details exactly how it must be communicated.
WSDL does not allow you to combine Web services or explain how to combine multiple services with their individual requests and responses into a more complex composite application.
Universal Description, Discovery, and Integration (UDDI) – defines a directory of businesses and the Web services they provide. Users can access the directory, discover services that exist, and download and use the WSDL definition for the Web services they require.
Some UDDI directories are public; that is, anyone can review and use the Web services they find there. Other UDDI directories are private; for example, Web services for a specific enterprise.
WARNING! Public UDDIs may contain inaccurate or incorrect data.
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