Overview of Web Services

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Chapter 14 Invoking and Implementing Web Services : Overview of Web Services

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.

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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.

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

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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.

Figure 43 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.

Figure 43 A typical interaction between web service client and server

TIBCO ActiveMatrix BusinessWorks can act as either a web service client or a web service provider. Process definitions can act as web service clients and invoke web service operations by using the activities in the SOAP palette. See The SOAP Palette for more information about how to invoke web services within a process definition.

There are two approaches to implementing web services as a web service provider in TIBCO ActiveMatrix BusinessWorks. The SOAP Event Source process starter creates a simple service with one operation over one transport. The Service resource allows you to create a service that implements multiple operations offered over multiple transports. See The Service Palette and The SOAP Palette for more information about using TIBCO ActiveMatrix BusinessWorks as a web service provider.