Case Study:

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Apple provide the ability for their customers to purchase the new iPhone $12$ mobile phone online through their system. As part of their policy, Apple allow a customer to only purchase a maximum of $3$ devices. After filling the shopping cart, the system will need to check if there are more than $3$ devices in the shopping cart. If not, then the system will provide the ability to add optional accessories to the devices. Then the system will show the customer the total amount of his order and the customer can make the payment. In case there are more than $3$ devices in the shopping cart, then the system will logoff the user. Also, note that the maximum number of items

in a shopping cart for one order is $10.$ the customer needs to login into the system before making orders. Please note that the system will display a confirmation message for each process that needs a confirmation.

Draw a system sequence diagram $($SSD$)$ for the above scenario.