Implementation of MLS/DBMS Models - Multilevel Security for Relational Databases - page 40

Get user class L(user)

Set i = 1

Get t(A i ) that satisfy P

i = i + 1

No

C PK = L(user)

Ye s

Delete t(Ai) i )

End

Figure 3.4 Flow chart for delete operation in SeaView and Jajodia-Sandhu models.

3.3 Jajodia-Sandhu Model

3.3.1 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 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 imple-
mented as follows [31]:

• Step 1: get the security level of the subject that runs the select
operation.
• Step 2: make a logical view over the stored single-level rela-
tions that perform the union operation between horizontal
single-level relations.