Assignment two
Birzeit Travel Vehicles (BTV) sells new recreational vehicles and travel trailers. When new vehicles arrive at BTV, a new vehicle record is created. Included in the new vehicle record is a vehicle serial number, name, model, year, manufacturer, and base cost.
When a customer arrives at BTV, s/he works with a salesperson to negotiate a vehicle purchase. When a purchase has been agreed to, a sales invoice is completed by the salesperson. The invoice summarizes the purchase, including full customer information, information on the trade-in vehicle (if any), the trade-in allowance, and information on the purchased vehicle. If the customer requests dealer-installed options, they will he listed on the invoice as well. The invoice also summarizes the final negotiated price, plus any applicable taxes and license fees. The transaction concludes with a customer signature on the sales invoice.
A. identify the classes described in the above scenario (you should find six). 
Customers are assigned a customer ID when they make their first purchase from BTV. Name, address, arid phone number are recorded for the customer. The trade-in vehicle is described by a serial number, make, model, and year. Dealer-installed options are described by an option code, description, and price.
B. Develop a list of attributes for each of the classes.
Each invoice will list just one customer. A person does not become a customer until they purchase a vehicle. Over time, a customer may purchase a number of vehicles from BTV.
Every invoice must be filled out by only one salesperson. A new salesperson may not have sold any vehicles, but experienced salespeople have probably sold many vehicles.
Each invoice only lists one new vehicle. If a new vehicle in inventory has not been sold, there will be no invoice for it. Once the vehicle sells, there will be just one invoice for it.
A customer may decide to have no options added to the vehicle, or may choose to add many options. An option may be listed on no invoices, or it may be listed on many invoices.
A customer may trade in no more than one vehicle on a purchase of a new vehicle. The trade-in vehicle may be sold to another customer, who later trades it in on another BTV.
C. Based on the above business rules in force at BTV, 
D. Choose one of the more complex classes and create statechart diagram for it.
E. develop a use case that describe a typical sales process. Then create a sequence diagram for the use case.