Implementation of MLS/DBMS Models - Multilevel Security for Relational Databases - page 39

Get user class L(user)

Set i = 1

Get t(A i ) that satisfy P

C PK = L(user)

i = i + 1

Ye s No

C PK = L(user)

Update t(A i )

Ye s No

Polyinstantiate t(Ai) i )

End

Figure 3.3 Flow chart for update operation in SeaView and Jajodia-Sandhu models.

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 MLS relation R,
for all t ∈ R, if t satisfies P, the delete operation is implemented as
fol lows [30]:

• Step 1: get the security level of the subject that runs the
delete operation.
• Step 2: delete all tuples from single-level relations 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
SeaView model.