hi I'm creating a project and i just need some guidance on if my ERD is designed right so i can move on to creating tablesTips and welcomed!...thx...Here are the business rules.
The Ocean Ford dealership wishes to manage data about their car sales. They are interested in keeping information about their customers. They wish to record data about all customers, whether they purchase a car or not Ė this data includes, name, address, phone and what marketing tool brought them into the dealership (recent newspaper ad about a particular vehicle, TV commercial, word of mouth or radio commercial).
When customers leave without purchasing a vehicle, the dealership wishes to ensure a methodical follow up strategy is taken. The dealership wants to record the following:
(1) the date and salesperson who places a telephone call to the customer thanking them for their visit and inviting them to return, as well as the customerís response;
(2) The date and the name of the sales manager who places a telephone call to the customer thanking them for their visit and inviting them to return, as well as the customerís response to the telephone call and;
(3) The date a letter from the owner or Ocean Ford is sent to the customer thanking them for their visit.
When customers purchase a new vehicle the dealership wishes to record for tracking purposes whether the car purchased is on order or is in current inventory. When a customer purchases a previously owned vehicle they wish to record whether the customer purchases an extended warranty and the mileage at the time of sale.
Ocean Ford also wishes to maintain data about their inventory new and previously owned. Data about cars, trucks, SUVs and minivans include: vehicle identification number, model, exterior color, interior color and year. The cars, Focus and Mustang, both have the additional attribute, package; while the Five Hundred model has the unique attribute, body style. Trucks have a few unique attributes (with the exception of the 2005 E series): cab, box, drive and doors. The SUVs, Escape, Explorer, and Excursion, have the unique attributes, drive and engine. The SUVs, Explorer Sport Track and Expedition, just has the attribute, drive. Although Ocean Ford is contemplating adding commercial trucks to their inventory, currently there are no other types of vehicles in Ocean Fordís inventory. Obviously a vehicle can be only one kind of vehicle at a particular time.
A customer may purchase one or more new or used vehicles from inventory and each vehicle is purchased by one or more customers (a new car in inventory may be traded in the next year, entered into inventory and then sold to another customer.) The organization is interested in the date of purchase, amount of sale and salesperson(s) completing the sale.
A hint: whenever you find a many-to-many relationship in ER modeling, break it out as an associative entity and think about:
1) does it correspond to anything in the real world
2) can you hang any attributes on it
sometimes the answer is NO to both the above, in which case forget about it till the physical design.