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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