The most distinctive difference between VisualWorks and Smalltalk Express is that VisualWorks uses a different, more complex approach to separating user-interface classes and instances from those classes and instances that are not part of the user interface. VisualWorks's approach is called the model–viewer–controller paradigm. In this chapter, you learn how model instances communicate with dependent-part instances and with controller instances.

In this chapter's illustrations, you see various objects manually assigned to global variables. Such manual assignment to global variables is for illustration only; ordinarily, a GUI builder attaches models, viewers, and controllers to one another using instance variables, as described in Chapter••missing reference••.