$($Activity Diagrams$)$

$($a$)$ Create an Activity Diagram for the scenario described below. Ensure that all diagram elements are given appropriate labels.

The owners of a small retail company make regular orders to their supplier. First, they check their current stock, and then compile the order. Once they receive the goods, they check them against the order. Then they update stock levels, and they also pay the supplier's bill.

Draw an activity diagram to illustrate the ordering process.

Hint:

Consider that update stock levels and pay the supplier's bill are performed concurrently.

$($b$)$ The diagram shown below is an activity diagram, illustrating the purchase of a book over the Internet. Study the diagram and the statements that follow it$.$ Indicate whether each statement is true or false, according to the diagram.

$($i$)$ Customer details must be recorded before the amount owing is calculated.

$($ii$)$ If the title is not available, a new title is input.

$($iii$)$ The transaction must always be confirmed immediately after the credit card details are recorded.

$($iv$)$ The credit card details must be recorded before the transaction is confirmed.

$($v$)$ Customer details are only recorded if the title chosen is available.

$($c$)$ Explain what an activity diagram is$,$ why and when it is used in Object Oriented system analysis.