Overview of Web Services

An organization can offer its application services to other organization by using the standards-based model of web services. Web services can be used within a business to integrate various critical applications, or web services can be made available to other businesses or individuals.

Web services rely on a variety of published standards for communication, security, data exchange, and so on. Standards-based technology enables businesses and individuals to use each other’s web services, regardless of the underlying applications or implementations of the service. Most web services comply with the following standards:

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HyperText Transfer Protocol (HTTP) or Java Message Service (JMS) — HTTP and JMS are transports, that is mechanisms for relaying information. Web services use a transport mechanism such as a Web server or JMS server to store and relay messages. TIBCO ActiveMatrix BusinessWorks supports HTTP and JMS as transports for web service messages.

●	Simple Object Access Protocol (SOAP) version 1.1 or 1.2 — SOAP is the communications protocol for web services. SOAP defines message structure and bindings to the underlying transports.

●	EXtensible Markup Language (XML) — XML is used to define data schemas for SOAP message content.

●	Web Service Definition Language (WSDL) — WSDL describes the interface to a web service. A web service provider publishes a WSDL file that describes the offered service. A client uses the WSDL file to determine the appropriate input, output, and fault messages for the service.

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Web Service Security (WS-Security) — WS-Security specification defines the standards-based approach to message-level security. Unlike transport-level session security (such as HTTPS), message-level security allows you to secure messages that may travel through multiple hops on a distributed transport channel. Message-level security is important for organizations that require trusted, secure communication between web services and clients.

The World Wide Web Consortium (W3C) maintains the standards upon which web services are based. See http://www.w3.org/ for more information about the currently supported web services standards.

Figure43 illustrates a typical interaction between a web service client and server. In this example, the web service provider uses HTTP as the underlying transport for sending and receiving messages. The client first retrieves the interface for the web service by requesting the WSDL file. Retrieving the WSDL file can be done either through a direct request to the service provider (as illustrated) or by searching well-known directories of web services. See WSIL Files and UDDI Registries for more information about using directories of web service providers.

Next, the client invokes an operation in the service by sending a SOAP message with the appropriate input defined in the WSDL. The web service executes the appropriate implementation and either successfully completes (and optionally sends a message containing the results of the operation) or sends a fault message detailing any errors encountered during the operation. Operations can be one-way (no information returned) or request-response (a response message is returned). If the operation returns information, the client then processes the information.