2. (a) In the context of Object Oriented Analysis and Design, when designing the structural model, what are the implications of designing a bi-directional association between two classes in terms of its implementation (as opposed to a uni-directional association). Illustrate your answer using code examples. (b) [10 Marks] (i) Explain the Principle of Least Knowledge. As part of your answer, outline three practical guides to object communication that Demeter promotes. Use UML to illustrate your answer. [9 Marks] (ii) Discuss, using an example of your choosing, how a behavioural model (sequence diagram) could be created which fully and correctly realises a specific use case but does not conform to its structural model (class diagram). [14 Marks]