8.1 Concepts The virtual application capabilities in the IBM Workload Deployer are based on the concept of standardized application-centric pattern solutions. The use of standard patterns allows developers of applications in cloud environments to focus on the application and its requirements instead of the middleware infrastructure and the often complex configuration of the middleware products needed to deploy them. Virtual application patterns define the resources required to support virtual applications, including web applications, databases, user registries, and more. These patterns are the deployment unit for a virtual application. The underlying structure for virtual application patterns is pattern types . Pattern types are the containers of solution-specific and topology-specific resources that are required for different types of virtual applications. The pattern types also provide shared services that incorporate runtime services, such as caching service and elastic load balancing. Pattern types contain plug-ins that provide the parts of the application and the lifecycle management of the parts (installation, configuration, start, stop, failure and recovery, and so on). The plug-ins contribute the components, links, and policies used to assemble virtual applications. Before building a virtual application using a virtual application pattern, you must enable the pattern types that are needed to provide the components of the pattern. The pattern types fall into the following primary categories: Web Application Pattern types Database pattern types Foundation Pattern type