Plugging in to component models
The concept of component architectures is the creation of reusable objects and the development of custom end-user software by appropriate assembly. In this light, the roles of component developers and application composers become distinctively separate. Component developers develop generic components whereas application composers focus on the domain of application by assembling and configuring generic, 'off-the-shelf' components. A component adheres to a component model, which provides the standard for component implementation and interoperability. In other words, a component model governs how to construct individual components and at the same time how those components globally communicate and interact with each other. Several component models exist, which have been standardized for the creation of such composable components. However different component models are not compatible and thus composition with other models is not possible. To solve the problem of interoperability and composability of components across different component models, the EU-funded project EASYCOMP, which stands for Easy Composition in Future Generation Component Systems, introduced a prototype system - the Component Workbench based on Vienna Component Framework. The Vienna Component Framework (VCF) was built to access different component models in a uniform way. VCF supports the interoperability and composability of components across different models allowing their reuse within one single application. The VCF presents a unified component model, implemented by a facade component, to the application programmer. In this way it simplifies the use of different component models and reduces their inherent difficulties. VCF uses plug-ins, which act as connectors that link components with predefined communication semantics, providing access to a component model. Such plug-ins have been implemented for JavaBeans, Enterprise JavaBeans, Microsoft COM+ and CORBA distributed objects. The Component Workbench (CWB) is a flexible toolkit for the composition of components. It is a graphical composition environment allowing developers to construct compositions out of existing components in a graphical and interactive way. Due to CWB's modular design and a generic uniform component model used for the internal representation of the components, it is possible to compose different component models and use their features in the same project. It uses VCF to allow the use of arbitrary component models. Through the Component Workbench based on Vienna Component Framework a wide range of software components can be accessed without limitations arising from model type. Furthermore if provides a basis for detailed comparison of different component models.
