Implementation of MLS/DBMS Models - Multilevel Security for Relational Databases - page 43

• Step 3: for each tuple in the tuples in step 2, if the security
level of the primary key is equal to the security level of the
user, the tuple in the single level will be updated.
• Step 4: for each tuple in the tuples in step 2, if the security
level of the primary key is lower than the security level of the
user, the tuple in the single level will be polyinstantiated at
the security level of the user.
Figure 3.3 illustrates the flow chart for the update operation in the
Jajodia-Sandhu model.
3.3.4 Delete Operation Procedure
The SQL statement for the delete operation is described as follows:
DELETE
FROM R
WHERE P
where R is an MLS relation and P is a delete condition that defines
the tuples that are to be deleted.
If a subject with the security class level L runs a command to delete
tuples from an MLS relation R, for all t ∈ R, if t satisfies P, the delete
operation is implemented as follows [31]:
• Step 1: get the security level of the subject that runs the delete
operation.
• Step 2: delete all tuples that satisfy delete condition P in the
delete statement and have a security level equal to the security
level of the user.
Figure 3.4 illustrates the flow chart for the delete operation in the
Jajodia-Sandhu model.
3.4 Smith-Winslett Model
3.4.1 Select Operation Procedure
The SQL statement for the selected operation is described as follows:
SELECT [A 1 ,A 2 ,...,A n ]
FROM R
WHERE P