Web services
If you have an existing application, and you want to make the service that your application provides available to others - either within your own organization or beyond it - you can use Web services technologies to provide a standard Web interface for your service. Web services can be defined as middleware that connects applications together no matter how each application is implemented or where it is located.
Web services operate at a level of abstraction that is similar to the Internet; they can work with any operating system, hardware platform or programming language that can be Web-enabled and are one of the technologies that you can use to implement a service-oriented architecture (SOA).
The core technologies on which Web services are developed and implemented include:
- XML
Solves the problem of data independence. Use it to describe data, and to map data into and out of any application or programming language.
- Web Services for J2EE
Defines the programming model and run-time architecture for implementing Web services based on the Java language. WAS V6.0 is supports Web Services for J2EE V1.1.
- Java API for XML-Based RPC (JAX-RPC)
Enables you to develop SOAP-based interoperable and portable Web services and Web services clients. WAS Version 6.0 supports JAX-RPC V1.1.
- Web Services Description Language (WSDL)
XML-based language used to create a description of an underlying application. This description turns an application into a Web service, by acting as the interface between the underlying application and other Web-enabled applications. WAS V6.0 supports WSDL Version 1.1.
- SOAP
Core communications protocol for the Web, and most Web services use this protocol to talk to each other.
- SOAP with attachments API for Java (SAAJ)
Used for SOAP messaging that works behind the scenes in the Java API for XML-based RPC (JAX-RPC) implementation. You can also use this API to directly write SOAP messaging applications rather than using JAX-RPC. SAAJ allows you to do XML messaging from the Java platform by making method calls by creating, sending and consuming XML messages over the Internet. WAS V6.0 and later supports SAAJ V1.2
WAS also provides other mechanisms that can help you get the most out of your Web services:
- Private Universal Description, Discovery and Integration (UDDI) registry
- A private UDDI registry provides a way to publish and discover information about Web services that are available within and through your organization. You can use it to make your Web services available to people within your organization, or beyond your organization. A group of companies can use it to share their Web services, or to make them available to others outside the group.
At its simplest, a private UDDI registry does for Web services what a business telephone directory does for business addresses and telephone numbers. However, a private UDDI registry is much more than just a directory. It needs to be in order to harness the considerable power and flexibility of Web services. If you publish your Web service to UDDI, you make it available for other people or applications to discover and reuse. This saves development time, effort and cost, and helps minimize the need to maintain several different implementations of the same application.
- Web Services Invocation Framework (WSIF)
- SOAP bindings for Web services are part of the WSDL specification. So when you think of using a Web service, you probably think of assembling a SOAP message and sending it across the network to the service endpoint, using some SOAP client API.
The WSDL specification allows for extensibility points which can describe alternate ways of invoking a Web service. A WSIF client can make use of these non-SOAP descriptions to invoke a service in a more efficient way. For example, a Web service provider might offer a SOAP binding for the service and a local Java binding that allows you to treat the local service implementation (a Java class) as a Web service. If the client is deployed in the same environment as the service, then the local Java binding for the service can be used. This provides more efficient communication with the service by making direct Java calls rather than sending and receiving SOAP messages.
To deploy a Web service as a WSIF-enabled service, you first develop and deploy the Web service, then you develop the WSIF client based on the WSDL document for that Web service.
- Web services and the service integration bus (SIBus)
Web services can use the SIBus and the Web services gateway to provide a single point of control, access, and validation of Web service requests and to allow control of Web services that are available to different groups of Web service users. With SIBus-enabled Web services, you can achieve the following goals:
- Take an internally-hosted service that is available at a bus destination, and make it available as a Web service.
- Take an externally-hosted Web service, and make it available internally at a bus destination.
- Use the Web services gateway to map an existing service - either an internal service, or an external Web service - to a new Web service that appears to be provided by the gateway.
- WS-Notification
WS-Notification enables Web services to use the "publish and subscribe" messaging pattern. In this pattern a producing application inserts (publishes) a message (event notification) into the messaging system, having marked it with a topic that indicates the subject area of the message. Consuming applications that have subscribed to the topic and have the appropriate authority, receive an independent copy of the message that was published by the producing application.
WS-Notification also allows interchange of event notification between WS-Notification applications and other clients of the service integration bus. By exploiting other service integration bus functionality, you can also use this function to interchange messages with other IBM publish and subscribe brokers such as Event Broker or Message Broker.