Database Reference
In-Depth Information
Get user class L(user)
Set i = 1
Get t
i
that satisfy P
i = i + 1
No
t
i
[TC]= L(user)
Ye s
Display ti
i
End
Figure 3.6
Flow chart for select operation in Smith-Winslett and MLR models.
where R is an MLS relation, [
A
1
,A
2
,...,A
n
] are the attributes from
R, and P is the select condition that defines the tuples to be retrieved.
If a subject with the security class level L runs a command to select
tuples from an MLS relation R, the selection operation is imple-
mented as follows [32]:
• Step 1: get the security level of the subject that runs the selected
operation.
• Step 2: get all tuples that have a security level below or equal to
the security level of the subject that runs the selected operation.
Figure 3.6 illustrates the flow chart for a selection operation in the
Smith-Winslett model.
3.4.2 Insert Operation Procedure
The SQL statement for the insert operation is described as follows:
INSERT
INTO R [A
1
,A
2
,...,A
n
]
VALUES [a
1
,a
2
,...,a
n
]
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