The graphic vb_structure.gif shows an inverted tree of view definition objects, and identifies the required components (on the left) and the optional components (on the right). The required components are Key Templates (under which the diagram shows Extract Macro), View Templates (under which are Questions, and under that is Extract Macro), and Map (under which is DCM Questions). The optional components are Having (under which are Questions and Responses) and Where (which has Keys and RDCMs and DCMs under it).