Table 2 Symbols used in the reduction model

Sets and indices

U

Set of observations, indexed by x ∈ U

A

Set of risk factors related to the threats, indexed by a_ij ∈ A for all attributes

C

Set of conditional seaport risk factors, indexed by a_ij ∈ C_j

D

A decisional variable, indexed by a_ij ∉ D_j

V_a

Set of risk magnitude {1, 2, 3,…,h} indexed by f(x,a) ∈ V_a

I_B or B

Set of indiscernible relation, indexed by (x₁, x₂) ∈ I_B

I

Number of threat factors

J

Number of conditional risk factors

L

Number of observations

Parameters

K

Dependency degree

S

Importance degree

p₁

Classification ability

p₂

Reduction rate

p₃

Correction factor

Variables

k_B

Dependency degree for each indiscernible relation a_i ∈ I_B

F_B

Attribute reduction set

\(\overline{S }\)

Weight indicator