Dynamic upgrade of distributed software components

prop = false compound_prop = false name = JavaMediaFramework serviceProvider = providerAAA description = "" version = 1.1 TranscoderEngine : Component abstract_prop = false compound_prop = false name = TranscoderEngine serviceProvider = providerAAA description version = 2.0 Duplicator : Componentprop = false compound_prop = false name = TranscoderEngine serviceProvider = providerAAA description version = 2.0 Duplicator : Component abstract_prop = false compound_prop = false name = Duplicator serviceProvider = providerBBB description = "" version = 1.1 Transcoder : Componentprop = false compound_prop = false name = Duplicator serviceProvider = providerBBB description = "" version = 1.1 Transcoder : Component abstract_prop = true compound_prop = true name = Transcoder serviceProvider = providerAAA description = "" version = 1.2 TranscoderService : Serviceprop = true compound_prop = true name = Transcoder serviceProvider = providerAAA description = "" version = 1.2 TranscoderService : Service name = TranscoderService version = 2.1 Figure 22. An example component-based service compliant to the component model. Figure 22 depicts an example service. The service is called TranscoderService and consists of two top components: Transcoder and Duplicator. Whereas the latter is a simple service component, component Transcoder contains further subcomponents: JavaMediaFramework and TranscoderEngine. One key characteristics of the software component as described in section 2.3, is its composibility. A component may be composed of a number components. In terms of deployment, it means that a component may need to access some other components. This idea is expressed by component dependencies. In the model, class Component has access zero of more dependent Component objects. There are three classes of service components that differ in the terms of whether they consist of some service subcomponents and whether they directly refer to a code module. • Simple Component is a service component without any dependencies. It contains just a reference to a code module. • Compound Component is a service component consisting of subcomponents and having a reference to a code module. • Abstract Component is a service component consisting of subcomponents and having no reference to a code module. The relations between the classes modeling the concepts defined above are depicted in a class diagram in Figure 23.