Database Reference
In-Depth Information
The first step in obtaining information from an existing document is to identify and list all columns and
give them appropriate names. Figure 6-15 lists the columns you can determine from the invoice shown in
Figure 6-14.
InvoiceNumber
InvoiceDate
CustomerNumber
CustomerSoldToName
CustomerSoldToAddressLine1
CustomerSoldToAddressLine2
CustomerSoldToCity
CustomerSoldToState
CustomerSoldToZip
CustomerShipToName
CustomerShipToAddress
CustomerShipToCity
CustomerShipToState
CustomerShipToZip
CustomerPONumber
OrderNumber
OrderDate
ShipDate
CustomerRepNumber
CustomerRepLastName
CustomerRepFirstName
ItemNumber
ItemDescription
ItemQuantityOrdered
ItemQuantityShipped
ItemQuantityBackordered
ItemPrice
ItemAmount
Freight
InvoiceTotal
205
FIGURE 6-15
List of possible attributes for Holt Distributors invoice
The names the user chose for many of these columns might differ from the names you select, but this dif-
ference is not important at this stage. After interviewing the user, you might learn that a required column
was not apparent on the document you reviewed. For example, the shipping address for the customer shown
in Figure 6-14 did not require a second line, so you simply listed CustomerShipToAddress rather than
CustomerShipToAddressLine1 and CustomerShipToAddressLine2 in your preliminary list of columns
(see Figure 6-15). Some columns that you identify may not be required. For example, when the ship date
is the same as the invoice date, a separate ShipDate column is unnecessary. Clearly, the user
'
shelpis
needed to clarify these types of issues.
Next, you need to identify functional dependencies. If you are unfamiliar with the document you are
examining, you might not be able to determine its functional dependencies. In this case, you will need to
interview the user to determine the functional dependencies that exist. Sometimes you can make intelligent
guesses based on your general knowledge of the type of document you are studying. You may make mistakes,
of course, but you can correct them when you interview the user. After initially determining the functional
dependencies shown in Figure 6-16, you may find additional information.
