The various steps of data design can be explained in a very practical way by using two case studies. A case study is the best way of explaining ideas that can somewhat become too abstract without real examples. Chapters 1 through 5 are based on a single case study: "Car dealership". Chapter 6 consists of another case study that recapitulates all the notions seen in the previous chapters.
Suppose we've been contacted by a car dealer who wants to computerize parts of his business. Let's describe a little bit about this business. In Chapter 2, we will examine the data collecting phase for our system more formally.
This car dealer operates at a single address. They employ nine salespersons who dutifully welcome potential customers and show them the car models that are available on the floor. In addition, two store assistants handle car movements, and an office clerk takes notes about customers' appointments. Fontax and Licorne are the two fictitious brands offered by this dealer. Each brand has a number of models, for example Mitsou, Wanderer, and Gazelle.
We want to keep information about the cars' inventory and sales. The following are some sample questions that demonstrate the kind of information our system will have to deal with:
How many cars of Fontax Mitsou 2007 do we have in stock?
How many visitors test-drove the Wanderer last year?
How many Wanderer cars did we sell during a certain period?
Who is our best salesperson for Mitsou, Wanderer, or overall in 2007?
Are buyers mostly men or women (per car model)?
Here are the titles of some reports that are needed by this car dealer:
Detailed sales per month: salesperson, number of cars, revenue
Yearly sales per salesperson
Inventory efficiency: average delay for car delivery to the dealer, or to the customer
Visitors report: percentage of visitors trying a car; percentage of road tests that lead to a sale
Customer satisfaction about the salesperson
The sales contract
In addition to this, screen applications must be built to support the inventory and sales activities. For example, being able to consult and update the appointment schedule; consult the car delivery schedule for the next week.
After this data model is built, the remaining phases of the application development cycle, such as screen and report design, will provide this car dealer with reports, and on-line applications to manage the car inventory and the sales in a better way.