Implementation of MLS/DBMS Models - Multilevel Security for Relational Databases - page 47

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

Update t i

End

Figure 3.8 Flow chart for update operation in Smith-Winslett model.

Figure 3.9 illustrates the flow chart for the delete operation in the
Smith-Winslett model.

3.5 Multilevel Relational (MLR) Model

3.5.1 Select Operation Procedure

The SQL statement for the select operation is described as follows:

SELECT [A 1 ,A 2 ,...,A n ]
FROM R
WHERE P

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