The Instance-Based Multilevel Security Model - Multilevel Security for Relational Databases - page 151

8.2.1 Definition 1: The Property View [102]
The instance at a classification level L j is defined by if {( P if ,L j ) | P if , ∈ P,
L j ∈ L} where if is defined as the instance identifier, P if is defined as the
property view on the group of the properties ( P ), and L j is defined as
the classification level on the classification levels. A pair ( P if ,L j ) pres-
ents the property's view that belongs to the classification level L j .
For example, in instance1{(FirstName Ahmed, U), (Salary 100, S),
(Salary 100, U), (Address Tanta, TS), (Address Cairo, S)}, the S level
can access the following view:
Instance1{(FirstName Ahmed, U), (Salary 100, S),
(Salary 100, U), (Address Cairo, S)}.
The U level will access the following view:
Instance1{(FirstName Ahmed, U), (Salary 100, U)}.
Since the user with a lower classification level cannot read the
higher classification level data, the instance view at the U classifica-
tion level contains less data than the view at the S classification level.
8.2.2 Definition 2: The Class View [102]
The class is defined as Class_ID({ P if }, { u if }) where Class_ID is defined
as the class identifier, { P if } is defined as the group of properties, and
{ u if } is defined as the group of users defined on the system.
The class can define which instances will be involved in the class
and can include the data of which users have the ability to access this
class. For example, if a class is defined as Class1({FirstName, Salary,
Address}, {user1, user2}), an instance of the class will be defined
as follows: Instance1{(FirstName Ahmed), (Salary 110), (Address
Tanta)} of the class. An instance Instance2{(FirstName Mohammed),
(Salary 110)} does not belong to the class.
8.2.3 Definition 3: The Instance View at Classification Level L j [102]
The instance view at classification level L j , which is if {( P if , L q ) | P if ∈ P,
L q ≤ L j and L q L j ∈ L } is related to the Class({ P K }, { u if }) if the property
{ P K } is a subgroup of the property { P if }. A user with U classification
level can access Class({ P K }, { u if }) if the user U ∈ { u if }.