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The Web Service Architecture

Microsoft, IBM, and others have created a set of specifications and technologies surrounding their vision for Web service architecture of the future. These specifications fill in the gaps that SOAP and WSDL don't address. You can easily identify these specifications, as they follow the naming scheme WS-technology, where the technology is something like security. This architecture is a vision that is shared across the industry and includes many of the ideas presented in this chapter so far, such as modularity and building on Web standards. DEFINITION: FEDERATION

Federation is a design methodology for spreading out processes, components, and machines in a way that removes single points of failure. Instead, the pieces of a distributed system are federated out over the entire system. Federation enables you to distribute systems across organizational and trust boundaries, and seldom requires a single administrative server. DNS (domain name system) and Usenet are familiar examples of federated services.

This Web service architecture includes a distinct and credible vision for how all of the modular pieces are to be plugged together. This vision is for a set of related specifications that are

  • Standards based
  • Modular
  • Federated
  • General purpose

Definition: Rollover

A process of making resources and services available on a new system when the previous system fails. It is one of the most compelling reasons to use a federated design, but there are more!We've looked at why standards and modularity are a good idea. Federated designs are useful because they eliminate one of the key problems with most client-server applications: the reliance on a server.

Imagine you have a customer relations application that needs to retrieve customer information from a central server. With most distributed application technologies, you would be hard pressed to come up with a more federated design that would allow you to roll over in case of failure. Web services enable developers to create a more flexible design with ease. Gnutella, Freenet, and UDDI (Universal Description, Discovery, and Integration) are all popular distributed applications that are also federated ones. In part, their popularity is because of this nonlocalized design.

Another goal of Web service architecture is to be general purpose. In other words, a mature Web service architecture can be applicable both to high-end server machines and to compact devices such as a cell phone. This general-purpose design means that the standards you use and learn now will be applicable to a wide range of scenarios and targets.

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