Implementation of MLS/DBMS Models - Multilevel Security for Relational Databases - page 53

MLS relation R: for all t ∈ R, if t satisfies P, the uplevel operation is
implemented as follows [33]:
• Step 1: get the security level of the subject that runs the
uplevel operation.
• Step 2: get all tuples from the multilevel relation that satisfy
uplevel condition P in the uplevel statement and have a tuple
security level lower than or equal to the security level of the user.
• Step 3: for each tuple t′ in the tuples in step 2, a user tuple
t is constructed as follows. The primary key of tuple t and
its security level are equal to the primary key of the tuple
t′ and its class level. For each nonprimary key attribute in
the tuple t′ attribute, if the attribute is in a GET clause, the
attribute of tuple t and its security level will be equal to this
attribute of the tuple t′ and its class level. If the attribute is
not in the GET clause, the attribute of tuple t will be null and
its security level will be equal to the security level of the user.
• Step 4: if there is a tuple with a primary key and tuple class
equal to the primary key and tuple class of the user tuple t, this
tuple will be replaced by the user tuple. If there is no tuple,
the user tuple will be inserted into the multilevel relation.
Figure 3.13 illustrates the flow chart for the uplevel operation in the
MLR model.
3.6 Belief-Consistent Multilevel Secure Relational Data Model
3.6.1 Basic Procedures for Operations
3.6.1.1 Xview (Label) Procedure This procedure returns the visible
part of the security label for the user who executes it [34].
• Step 1: get the label as input parameter for the procedure.
• Step 2: break the label into parts.
• Step 3: get the security level of the subject that runs the procedure.
• Step 4: set the counter equal to 1.
• Step 5: while (counter ≤ user level), pack the new label with
parts that the user can see.
• Step 6: increment the counter by 1.
• Step 7: return the new label.