Data Modeling with the Entity-Relationship Model - Database Processing: Fundamentals, Design, and Implementation - page 197

(a) Suppliers Form

(b) PART Report

What is the difference? If you look closely, you'll see that the only difference is that the report
in Figure 5-21 contains Price, which is the price quotation for a part from a particular supplier. The
first line of this report indicates that the part Cedar Shakes is supplied by Bristol Systems for $14.00.
Price is neither an attribute of COMPANY nor is it an attribute of PART. It is an attribute
of the combination of a COMPANY with a PART. Figure 5-22 shows the appropriate data model
for such a case.
Here a third entity, QUOTATION, has been created to hold the Price attribute. The
identifier of QUOTATION is the combination of PartNumber and CompanyName. Note that

Figure 5-19
Form and Report Indicating
an N:M Relationship

COMPANY DEPARTMENT

Figure 5-20
Data Model for the N:M
Relationship in Figure 5-19

CompanyName DepartmentName

City
Country
Volume

BudgetCode
MailStop

PART

PartNumber

PartName
SalesPrice
ReOrderQuantity
QuantityOnHand