| Component-Based Software Development (CBSD) is widely used to improve de-velopment productivity and software quality. However, existing CBSD techniques be-come increasingly insufficient for applications situated in open computing environ-ments such as the Internet/WWW because they lack the support for the dynamic adap-tation to changes in the environments and requirements.An effective approach to the adaptability of distributed component-based systems is to allow the running components be dynamically updated. Unfortunately, main-stream component models and frameworks used in the industry have little support for dynamic updates, and component models with dynamic update support proposed in the academia are often oversimplified for practical use. In this paper, we extend the Service Component Architecture (SCA) to provide comprehensive dynamic update support. The contribution of this extension includes:·A distributed transaction model to provide information for dynamic update al-gorithms. The model defines transaction states, transition semantics between different states and state propagation among distributed components.·A system consistency model for safe update. The model assigns versions to com-ponents, explicitly manages the dependency between components, and builds system consistency criteria for dynamic update on top of the SCA component model.·A component lifecycle model for executing update. The model defines extra component states and transition semantics between different states. With thelifecycle model, distributed components can coordinate with each other to ac-complish the update without sacrificing system consistency.An implementation of the extended SCA has developed on top of Apache Tus-cany. With this implementation, as a case study, we successfully updated running components of a travel agent system. We also evaluated the disruption and the timeli-ness of dynamic updates. The results show that our extension is feasible, effective and efficient. |
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