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6.3.2 Polyinstantiation Integrity
In polyinstantiation integrity (PI), a multilevel relational database
instance r satisfies the polyinstantiation integrity if the following
requirement exists [78]:
For 1 ≤ i n:
A 1 , TC C i ;
and
A 1 , C 1 , C i A i ;
This property ensures that the primary key attribute A 1 , in conjunction
with the security classification level attributes C 1 and C i , functionally
determines the value of the A i attribute.
6.3.3 Data-Borrow Integrity
In data-borrow integrity (DBI), a multilevel relational database instance
r satisfies the data borrow if the following requirement exists [79]:
For 1 ≤ i n, all the nonprimary key attributes in tuple t r that
have data encrypted by key according to security classification levels
lower than the tuple classification level, there exists polyinstantiated
tuple t ′ that has
t ′[ A 1 ] = t [ A 1 ] ∧ t ′[ TC ] = t ′[ c i ] = t [ c i ] ∧ t ′[ A i ] = t [ A i ].
6.3.4 Foreign Key Integrity
In foreign key integrity (FKI), let FK be a foreign key of the referenc-
ing relation R . A multilevel relational database instance r satisfies the
foreign key if the following requirement exists [79]:
For each tuple t r:
(∀ A i FK ), t [ A i ] ≠ null
and
A i , A i FK t [ C i ] = t [ C i ]
The first requirement of this property ensures that no foreign key
attribute in the referencing relation has a null data value. The second
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