Database Reference
In-Depth Information
EMPLOYEE
COMPUTER
EmployeeNumber
SerialNumber
FirstName
LastName
Department
Phone
Email
Make
Model
ProcessorType
ProcessorSpeed
MainMemory
DiskSize
COMPUTER_ASSIGNMENT
EmployeeNumber
SerialNumber
DateAssigned
DateReassigned
Figure 7-33
WPC Data Model Extension
COMPUTER
ColumnName
Type
Key
Required
Remarks
SerialNumber
Number
Primary Key
Yes
Long Integer
Make
Text (12)
No
Yes
Must be “Dell”
or “Gateway” or
“HP” or “Other”
Model
Text (24)
No
Yes
ProcessorType
Text (24)
No
No
ProcessorSpeed
Number
No
Yes
Double [3,2],
Between 1.0
and 4.0
MainMemory
Text (15)
No
Yes
DiskSize
Text (15)
No
Yes
Figure 7-34
Column Characteristics for
the WPC COMPUtEr table
COMPUTER_ASSIGNMENT table are shown in Figure 7-35. Data for the COMPUTER
table are shown in Figure 7-36, and data for the COMPUTER_ASSIGNMENT table are
shown in Figure 7-37.
7.59
Describe the relationships in terms of type (identifying or nonidentifying) and maxi-
mum and minimum cardinality.
Figure 7-35
Column Characteristics
for the WPC COMPUtEr_
aSSIGNMENt table
7.60
Explain the need for each of the foreign keys.
COMPUTER_ASSIGNMENT
ColumnName
Type
Key
Required
Remarks
SerialNumber
Number
Primary Key,
Foreign Key
Yes
Long Integer
EmployeeNumber
Number
Primary Key,
Foreign Key
Yes
Long Integer
DateAssigned
Date
No
Yes
Medium Date
Medium Date
DateReassigned
Date
No
No
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