Implementation of MLS/DBMS Models - Multilevel Security for Relational Databases - page 49

where R is an MLS relation, A 1 ,A 2 ,...,A n are the attributes from
R, and a 1 ,a 2 ,...,a n are values from domains of A 1 ,A 2 ,...,A n .
If a subject with the security class level L runs a command to insert a
tuple into an MLS relation R, the insertion operation is implemented
as follows [33]:

• Step 1: get the security level of the subject that runs the insert
operation.
• Step 2: if the attribute is included in the attributes list in the
insert statement, this attribute will be set to its value from
the values list in the insert statement; otherwise, the value of
this attribute will be null.
• Step 3: the security level of all attributes will be equal to the
security level of the subject that runs the insert operation.
• Step 4: insert a new tuple with the attribute's values and its
security level into the multilevel relation.

Figure 3.10 illustrates the flow chart for the insertion operation in the
MLR model.

Get user class L(user)

Set i = 1

A i ∈ R [A i ]*

i = i + 1

No Ye s

A i = null A i = a i

C i = L(user)

Insert the row

End

Figure 3.10 Flow chart for insertion operation in MLR and belief-consistent models.