Implementation of MLS/DBMS Models - Multilevel Security for Relational Databases - page 57

3.6.1.4 Ib (Label) Procedure This procedure returns the belief of a
user from the security level L about information labeled by the label
L [34]—for example, L = ucs, Ib (S, L) = s.
• Step 1: divide the security class levels into parts.
• Step 2: get the security level of the subject that runs the procedure.
• Step 3: set the counter equal to 1.
• Step 4: while (counter ≠ user - level), the return value will be
equal to mod (L, number of class levels) and L will be equal
to L/number of class levels.
• Step 5: increment the counter by 1.
• Step 6: return value.
Figure 3.17 illustrates the flow chart for the Ib (label) procedure in the
belief-consistent model.
3.6.2 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 tuples from
an MLS relation R, the selection operation is implemented as follows [35]:
• Step 1: get all tuples that have an Xview (tuple class) not equal
to zero and satisfy selection condition P.
• Step 2: for each attribute in the attributes of each tuple in the
tuples in step 1, get Xview (attribute class).
Figure 3.18 illustrates the flow chart for the selected operation in the
belief-consistent model.
3.6.3 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 ]