User acceptance of a knowledge-based system depends partly on how effective the system is in explaining its reasoning and justifying its conclusions. The WOZ framework provides effective explanations for component-based decision-support systems. It represents explanation using explicit models, and employs a collection of visualization agents. It blends the strong features of existing explanation strategies, component-based systems, graphical visualizations, and explicit models. We illustrate the features of WOZ with the help of a component-based medical therapy system. We describe the explanation strategy, the roles of the visualization agents and components, and the communication structure. The integration of existing and new visualization applications, the domain-independent framework, and the incorporation of varied knowledge sources for explanation can result in a flexible explanation facility.