Database Reference
In-Depth Information
understand that term functional dependency; therefore, it is important to ask the right questions
so that you can identify any functional dependencies. An accurate list of functional dependen-
cies is absolutely essential to the design process.
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Processing information. The survey form should include a description of the manner in which
the various types of processing (updates to the database, reports that must be produced, and so
on) are to take place. To obtain this information, you would pose questions such as these:
￿
How exactly is the report to be produced?
￿
Where do the entries on the report come from?
204
￿
How are the report entries calculated?
￿
When a user enters a new order, from where does the data come?
￿
Which entities and columns must be updated and how?
In addition, you need to obtain estimates on processing volumes by asking questions such as these:
￿
How often is the report produced?
￿
On average, how many pages or screens is the report?
￿
What is the maximum length of the report?
￿
What is the maximum number of orders the system receives per day?
￿
What is the average number of orders the system receives per day?
￿
What is the maximum number of invoices the system prints per day?
￿
What is the average number of invoices the system prints per day?
OBTAINING INFORMATION FROM EXISTING DOCUMENTS
Existing documents can often furnish helpful information concerning the database design. You need to take
an existing document, like the invoice for the company named Holt Distributors shown in Figure 6-14, and
determine the tables and columns that would be required to produce the document.
10/15/2013
Invoice 11025
HOLT DISTRIBUTORS
146 NELSON PLACE
BRONSTON, MI 49802
SOLD
SHIP
TO:
Smith Rentals
TO:
A & B Supplies
153 Main St.
2180 Halton Pl.
Suite 102
Arendville, MI 49232
Grandville, MI 49494
Customer
P.O. No.
Our Order No.
12424
Order Date
Ship Date
10/15/2013
Sales Rep
10-Brown, Sam
1354
PO3351
10/02/2013
Quantity
Order
6
4
Ship
B/O
Item Number
AT414
BT222
Description
Price
Amount
$210.00
$204.00
5
4
1
0
Lounge Chair
Arm Chair
$42.00
$51.00
Freight
$42.50
Pay This Amount
$456.50
FIGURE 6-14
Invoice for Holt Distributors
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