(a) In the context of Object Oriented (OO) analysis, outline what a Use Case is. In your answer, identify three roles that use cases play in the implementation of an OO system. [5 Marks] (b) Discuss what an actor is within the context of a use case diagram and illustrate the UML notation that relates to it. [7 Marks] (c) Within a use case diagram, there are relationships that can exist between individual use cases, one is extends the other is includes. Explain what each relationship means, giving an example. [6 Marks] (d) Using an example of your choice, provide a documented use case using the following headings: - Purpose or Intent - High level description - Pre-conditions - Extended step by step description of main flow - Alternative flows (or scenarios) - Post-conditions