Virtualization is a buzzword that is living up to its hype as it takes hold in IT. It has spawned magazine covers, conferences, and analyst reports, and all with good reason. Virtualization allows applications to be deployed in a highly efficient manner. By taking the physical servers out of the equation, virtualization allows applications to be deployed across a number of servers, or for multiple operating systems to run simultaneously on one server. In this way, an organization can scale its applications by seamlessly adding hardware, or by adding more instances of operating systems to its servers.

In the world of Web Services, in a "service-oriented architecture" (SOA), applications are deployed as services over the network. This means that if an application wants to use components of another application, it simply accesses this other application over the network. The services in an SOA are both language- and platform-neutral, so they can be called from .NET applications or Java applications, in Windows, Linux, or Solaris. How does virtualization apply to SOA? In this article, we look at the intersection of SOA and virtualization, which is service virtualization.

"Service virtualization" is made possible by XML gateways. Over the past three years, XML gateways have emerged as a prime delivery platform for XML applications. An XML gateway is either delivered as an appliance or as software. It proves functionality that is essential to the successful delivery of Web Services, such as security, XML processing acceleration, and XML routing. XML gateways effectively "front" back-end Web Services by creating so-called "virtual services" that act as proxies in front of the real services. For example, if an organization has used .NET to create a Web Service called "calculateStateSalesTax", then an XML gateway can be used to create a virtual service in front of the service. Then, the client accesses the virtual service at the XML gateway rather than the actual Web Service.

This architecture is depicted in Figure 1. Clients can now connect to the virtual services rather than directly to the Web Services. The XML gateway makes this possible.