Database Reference
In-Depth Information
C
i
= L(user)
K = K
Ci
Set i = 1
i = i + 1
t
i
[TC] = L(user)
No
Ye s
t
i
= D (K, E (K, t
i
))
No
t
i
satisfy P
Ye s
Display ti
i
End
Figure 5.3
Flow chart for the select operation in the encryption-based multilevel database
model. (X.-D. Zuo, F.-M. Liu, and C.-B. Ma. 2007.
Proceedings of the Sixth International Conference on
Machine Learning and Cybernetics,
Hong Kong, 2158-2163.)
5.3.4 he UPDATE Statement
The UPDATE statement executed by a subject with security class
level L has the following general form:
UPDATE R SET [A
1
= a
1
, A
2
= a
2
,...,A
n
= a
n
]
WHERE P
where R is the relation name;
[A
1
,A
2
,...,A
n
]
are the attribute names;
and P is a predicate expression that may include conditions involv-
ing classification attributes. Only tuples
t
∈
r
with
t
[
TC
] =
L
will be
decrypted by key according to the classification level of the subject that
executes the select statement and will be taken into the calculation of P.
For decrypted tuples
t
∈
r
that satisfies the predicate P, r is updated
as follows:
• Create a temporary tuple for decrypted data to store the deleted
tuple during the execution of the DELETE statement.
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