Unit 4 discusses object oriented design processes and axioms. The key points are: 1. The object oriented design process involves defining classes, methods, attributes and associations, applying design axioms to refine UML diagrams, and testing design satisfaction through use cases. 2. There are two main axioms - maintaining independence of components and minimizing information content. 3. Corollaries derived from the axioms include uncoupled design with less information, single purpose classes, large number of small reusable classes, strong mapping from analysis to implementation, standardization, and inheritance-based design.