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Cost-sensitive three-way class-specific attribute reduction
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The theory of rough sets provides a method to construct three types of classification rules, leading to three-way decisions. From such a point of view, we introduce the concept of cost-sensitive three-way class-specific attribute reducts. Based on the semantics of the three-way decisions, we introduce a monotonic result cost in decision-theoretic rough set model, called the result cost of three-way decisions. We provide a critical analysis of classification-based attribute reducts from result-co
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International Journal of Approximate Reasoning 105 (2019) 153–174
Contents lists available at ScienceDirect
International Journal of Approximate Reasoning
www.elsevier.com/locate/ijar
Cost-sensitive three-way class-specific attribute reduction
Xi-Ao Ma
a,∗
, Xue Rong Zhao
b
a
School of Computer and Information Engineering, Zhejiang Gongshang University, Hangzhou, Zhejiang 310018, China
b
School of Mathematics and Statistics, South-Central University for Nationalities, Wuhan 430074, China
a r t i c l e i n f o a b s t r a c t
Article history:
Received
6 April 2018
Received
in revised form 20 November 2018
Accepted
21 November 2018
Available
online 27 November 2018
Keywords:
Cost-sensitive
three-way decision
Attribute
reduction
Decision-theoretic
rough set
The theory of rough sets provides a method to construct three types of classification
rules, leading to three-way decisions. From such a point of view, we introduce the
concept of cost-sensitive three-way class-specific attribute reducts. Based on the semantics
of the three-way decisions, we introduce a monotonic result cost in decision-theoretic
rough set model, called the result cost of three-way decisions. We provide a critical
analysis of classification-based attribute reducts from result-cost-sensitive and test-cost-
sensitive
perspectives. On this basis, we propose class-specific cost-sensitive attribute
reduction approaches. More specifically, we define a class-specific minimum cost reduct.
The objective of attribute reduction is to minimize result cost and test cost with respect
to a particular decision class. We design two algorithms for constructing a family of class-
specific
minimum cost reducts based on addition–deletion strategy and deletion strategy,
respectively. The experimental results indicate that the result cost of three-way decisions
is monotonic with respect to the set inclusion of attributes and the class-specific minimum
cost reducts can make a better trade-off between misclassification cost and test cost with
respect to a particular decision class.
© 2018 Published by Elsevier Inc.
1. Introduction
Three-way decisions [45], proposed by Yao, provide a practical way to human daily decision-making. It can be interpreted
within a trisecting-and-acting framework [48]. The universe is first divided into three pair-wise disjoint parts according
to trisecting. The acting then constructs and applies the most effective strategies to process the three parts. Three-way
decisions have been widely used in many fields and disciplines, such as clustering analysis [55], face recognition [11],
granular computing [29,44,49], linguistic assessment [15], pattern recognition [33,41,42], recommender systems [7,56], social
networks [30,54], software defect prediction [14], and fuzzy decisions [59–61]. In the theory of rough sets, proposed by
Pawlak [26–28], one divides the universe into three pair-wise disjoint parts, namely, the positive, boundary, and negative
regions. We can use the notion of three-way decisions to interpret rules. Specifically, one can construct acceptance rules from
the positive region and rejection rules from the negative region to make acceptance and rejection decisions, respectively.
For the boundary region, we make neither acceptance nor rejection decisions, but make non-commitment decisions. Pawlak
rough set model requires that both the acceptance and rejection decisions must be fully correct or certain, which does not
allow any tolerance of errors. Probabilistic rough set models [4,17,32,34,45,50,57,63]were proposed to make acceptance or
rejection decisions for more objects by allowing certain acceptable levels of errors.
*
Corresponding author.
E-mail
addresses: maxiao73559@163.com (X.-A. Ma), xrzhao@whu.edu.cn (X.R. Zhao).
https://doi.org/10.1016/j.ijar.2018.11.014
0888-613X/
© 2018 Published by Elsevier Inc.
154 X.-A. Ma, X.R. Zhao / International Journal of Approximate Reasoning 105 (2019) 153–174
The notion of attribute reducts plays a key role in attribute reduction [6,9,13,19,21,25,31,37,39,40,58]. An attribute reduct
is a minimal subset of attributes serving the same purpose as the entire set of attributes [47]. There are two types of at-
tribute
reducts, namely, classification-based attribute reducts [27] and class-specific attribute reducts [1,2,18,20,35,36,51].
A classification-based attribute reduct usually chooses the same set of attribute reducts for all decision classes. A class-
specific
attribute reduct allows for different sets of attribute reducts for different decision classes. Since different attributes
may have different capabilities in discriminating different decision classes, a class-specific attribute reduct enables us to
select an attribute reduct that is most suitable for a particular decision class. In terms of the two types of attribute reducts,
three-way attribute reducts have received much attention in recent years. Zhang and Miao [58]investigated a framework of
three-way classification-based attribute reducts. Yao and Zhang [51]introduced the notion of class-specific attribute reducts
by considering only the positive region of a particular decision class. From three-way decision perspectives, Ma and Yao [20]
examined
three types of class-specific attribute reducts that respectively focus on the positive region, the negative region,
and both the positive and negative regions of a particular decision class. However, these studies do not consider the cost. In
this paper, we study and introduce the concept of cost-sensitive three-way class-specific attribute reducts.
There
are two types of important costs, namely, result cost and test cost, in cost-sensitive three-way decision model.
The result cost is the cost of the decision result, that is, quality of the decision result in terms of costs caused by incorrect
decisions. Decision-theoretic rough set model can be regarded as a kind of cost-sensitive three-way decision model [11,12].
Jia et al. [8]proposed the concept of decision cost in decision-theoretic rough set model. The decision cost can be viewed
as a kind of result cost. The test cost is the cost needed for obtaining new information. For example, in medical practice, a
patient needs to take an X-ray test to diagnose the pneumonia, which will incur certain extra costs. In recent years, result
cost and test cost have attracted a great deal of interests and are widely studied in cost-sensitive attribute reduction.
According
to the result cost and test cost, we can classify cost-sensitive attribute reduction into two categories: result-
cost-sensitive
attribute reduction and test-cost-sensitive attribute reduction. For result-cost-sensitive attribute reduction, an
attribute reduct is defined by minimizing the result cost. Yao and Zhao [52] discussed cost criterion for attribute reduction
in decision-theoretic rough set model. Jia et al. [8] constructed an optimization problem with the objective of minimizing
the decision cost and defined a minimum cost reduct in decision-theoretic rough set model. Song et al. [35]proposed the
notion of minimal decision cost reducts in fuzzy decision-theoretic rough set model to deal with numerical data. For test-
cost-sensitive
attribute reduction, the main objective of attribute reduction is to minimize the test cost under the condition
of preserving sufficient information for classification. Min et al. [22]proposed a minimal test cost reduct and developed
the effective reduction algorithm. In a follow-up study, they [23]described attribute reduction problem concerning the test
cost constraint as a constraint satisfaction problem. Yang et al. [43] established test-cost-sensitive multigranulation rough
set and presented a backtracking algorithm and a heuristic algorithm for deriving a reduct with minimal test cost. Ju et al.
[10]proposed cost-sensitive rough set model by incorporating test cost into the indiscernibility relation.
In
this paper, we make a critical analysis of classification-based attribute reducts from the perspectives of result-cost-
sensitive
attribute reduction and test-cost-sensitive attribute reduction. In addition, we introduce a new result cost based on
the semantics of three-way decisions, called the result cost of three-way decisions. It meets the monotonicity with respect
to the set inclusion of attributes. The experiment results verify the monotonicity of the result cost of three-way decisions.
Based on the result cost of three-way decisions, we propose the notion of class-specific minimum cost reducts. A class-
specific
minimum cost reduct is a minimal subset of attributes satisfying the criterion that minimizes result cost and test
cost with respect to a particular decision class. The monotonicity of the result cost of three-way decisions provides a com-
putationally
efficient method for constructing a reduct. On this basis, we develop two heuristic algorithms for constructing
a family of class-specific minimum cost reducts based on addition–deletion strategy and deletion strategy [53], respectively.
In the end, we provide several experimental analyses on the performance between class-specific minimum cost reducts and
classification-based minimum cost reducts. Here, a classification-based minimum cost reduct is defined as a minimal subset
of attributes that minimizes result cost and test cost on all decision classes.
The
rest of this paper is organized as follows. Section 2 briefly reviews some basic notions related to three-way deci-
sions
with decision-theoretic rough sets. Section 3 provides a critical analysis of classification-based attribute reducts from
result-cost-sensitive perspective and test-cost-sensitive perspective. Section 4 presents the notion of class-specific minimum
cost reducts and designs two reduct construction algorithms for finding a family of class-specific minimum cost reducts.
Section 5 carries out some experimental analyses. Section 6 presents conclusions and outlines further research trends.
2. Three-way decision with decision-theoretic rough sets
Decision-theoretic rough sets can be viewed as a specific three-way decision model. In this section, we review some
basic notions related to decision-theoretic rough sets [16,50,62].
Definition
1. An information table is defined by a tuple:
T = (OB, AT , V ={V
a
| a ∈ AT}, I ={I
a
| a ∈ AT}), (1)
where OB is a finite nonempty set of objects called the universe, AT is a nonempty finite set of attributes, V
a
is a nonempty
set of values of an attribute a ∈ At, called the domain of a, and I
a
: OB → V
a
is a description function that maps an object
in OB to exactly one value in V
a
.
X.-A. Ma, X.R. Zhao / International Journal of Approximate Reasoning 105 (2019) 153–174 155
Table 1
Loss
functions.
D
j
D
j
a
P
j
a
B
j
a
N
j
a
P
j
a
B
j
a
N
j
D
1
λ
P
1
D
1
λ
B
1
D
1
λ
N
1
D
1
λ
P
1
D
1
λ
B
1
D
1
λ
N
1
D
1
D
2
λ
P
2
D
2
λ
B
2
D
2
λ
N
2
D
2
λ
P
2
D
2
λ
B
2
D
2
λ
N
2
D
2
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
D
j
λ
P
j
D
j
λ
B
j
D
j
λ
N
j
D
j
λ
P
j
D
j
λ
B
j
D
j
λ
N
j
D
j
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
D
m
λ
P
m
D
m
λ
B
m
D
m
λ
N
m
D
m
λ
P
m
D
m
λ
B
m
D
m
λ
N
m
D
m
Given a subset of attributes A ⊆ AT, an equivalence relation is defined by:
E
A
={(x, y) ∈ OB× OB|∀a ∈ A, I
a
(x) = I
a
(y)}. (2)
The equivalence relation induces a partition of OB denoted by π
A
= OB/E
A
={[x]
A
| x ∈ OB}, where [x]
A
={y ∈ OB |
(
x, y) ∈ E
A
}. A partition of OB is also called a classification.
A
decision table is a special type of information tables with AT = C ∪ D, where C is a set of condition attributes, D is
a set of decision attributes, and C ∩ D =∅. For brevity, a decision table is denoted by DT = (OB, C ∪ D). For any B ⊆ C ,
we have a partition π
B
. For the set of decision attributes D, we have a partition π
D
={D
1
, D
2
, ..., D
j
, ..., D
m
}, called a
decision classification of OB. Each equivalence class D
j
∈ π
D
is called a decision class.
Decision-theoretic rough set model [50]is a probabilistic extension of Pawlak rough set model [26,27]by a straight-
forward
application of the Bayesian decision theory. The set of states is given by a finite set of m decision classes
={D
1
, D
2
, ..., D
j
, ..., D
m
}. For simplicity, we use the same symbol to denote both a subset D
j
and the corresponding
state. For a m-class decision problem, we can convert it into m two-class decision problems. In general, the costs incurred
for misclassifying an object into different decision classes are different. For each decision class D
j
, the set of states is given
by
j
={D
j
, D
j
} indicating that an object is in D
j
and not in D
j
, respectively. Given a partition π
B
, the probabilities for
these two complement states are denoted as Pr(D
j
|[x]
B
) and Pr(D
j
|[x]
B
) = 1 − Pr(D
j
|[x]
B
). One can divide the universe
into three pair-wise disjoint positive region POS(D
j
|π
B
), boundary region BND(D
j
|π
B
), and negative region NEG(D
j
|π
B
).
The set of actions is denoted by A
j
={a
P
j
, a
B
j
, a
N
j
}, where a
P
j
, a
B
j
, and a
N
j
represent the three actions in classifying an
object x, namely, deciding x ∈ POS(D
j
|π
B
), deciding x ∈ BND(D
j
|π
B
), and deciding x ∈ NEG(D
j
|π
B
), respectively. The loss
functions are given by a m × 6matrix showed in Table 1.
In the matrix, λ
P
j
D
j
, λ
B
j
D
j
, and λ
N
j
D
j
denote the costs incurred for taking actions a
P
j
, a
B
j
, and a
N
j
, respectively, when
an object belongs to D
j
; λ
P
j
D
j
, λ
B
j
D
j
, and λ
N
j
D
j
denote the costs incurred for taking actions a
P
j
, a
B
j
, and a
N
j
, respectively,
when an object does not belong to D
j
.
The expected costs associated with taking individual actions for objects in [x]
B
with respect to the decision class D
j
can
be expressed as follows:
R(a
P
j
|[x]
B
) = λ
P
j
D
j
Pr(D
j
|[x]
B
) + λ
P
j
D
j
Pr(D
j
|[x]
B
),
R(a
B
j
|[x]
B
) = λ
B
j
D
j
Pr(D
j
|[x]
B
) + λ
B
j
D
j
Pr(D
j
|[x]
B
),
R(a
N
j
|[x]
B
) = λ
N
j
D
j
Pr(D
j
|[x]
B
) + λ
N
j
D
j
Pr(D
j
|[x]
B
).
The Bayesian decision procedure leads to the following minimum-risk decisions:
(P) If R(a
P
j
|[x]
B
) ≤ R(a
B
j
|[x]
B
) and R(a
P
j
|[x]
B
) ≤ R(a
N
j
|[x]
B
),
decide x ∈ POS(D
j
|π
B
);
(
B) If R(a
B
j
|[x]
B
) ≤ R(a
P
j
|[x]
B
) and R(a
B
j
|[x]
B
) ≤ R(a
N
j
|[x]
B
),
decide x ∈ BND(D
j
|π
B
);
(
N) If R(a
N
j
|[x]
B
) ≤ R(a
P
j
|[x]
B
) and R(a
N
j
|[x]
B
) ≤ R(a
B
j
|[x]
B
),
decide x ∈ NEG(D
j
|π
B
).
Tie-breaking criteria should be added so that each object is classified into only one region. Consider a special type of loss
function with the following constraints:
(C1)λ
P
j
D
j
≤ λ
B
j
D
j
<λ
N
j
D
j
,
λ
N
j
D
j
≤ λ
B
j
D
j
<λ
P
j
D
j
.
156 X.-A. Ma, X.R. Zhao / International Journal of Approximate Reasoning 105 (2019) 153–174
That is, the cost of classifying an object x
belonging
to D
j
into the positive region POS(D
j
|π
B
) is less than or equal to
the cost of classifying x
into
the boundary region BND(D
j
|π
B
), and both of these costs are strictly less than the cost of
classifying x
into
the negative region NEG(D
j
|π
B
). The reverse order of costs is used to classify an object not in D
j
. By
Pr(D
j
|[x]
B
) + Pr(D
j
|[x]
B
) = 1, we can simplify the decision rules (P)–(N) under the condition (C1). The first condition in
rule (P) can be expressed as follows:
R(a
P
j
|[x]
B
) ≤ R(a
B
j
|[x]
B
)
⇐⇒ λ
P
j
D
j
Pr(D
j
|[x]
B
) + λ
P
j
D
j
Pr(D
j
|[x]
B
) ≤ λ
B
j
D
j
Pr(D
j
|[x]
B
) + λ
B
j
D
j
Pr(D
j
|[x]
B
)
⇐⇒ λ
P
j
D
j
Pr(D
j
|[x]
B
) + λ
P
j
D
j
(1 − Pr(D
j
|[x]
B
)) ≤ λ
B
j
D
j
Pr(D
j
|[x]
B
) + λ
B
j
D
j
(1 − Pr(D
j
|[x]
B
))
⇐⇒
Pr(D
j
|[x]
B
) ≥
(λ
P
j
D
j
− λ
B
j
D
j
)
(λ
P
j
D
j
− λ
B
j
D
j
) + (λ
B
j
D
j
− λ
P
j
D
j
)
.
Similarly, other conditions in rules (P)–(N) can be expressed as follows:
R(a
P
j
|[x]
B
) ≤ R(a
N
j
|[x]
B
) ⇐⇒ Pr(D
j
|[x]
B
) ≥
(λ
P
j
D
j
− λ
N
j
D
j
)
(λ
P
j
D
j
− λ
N
j
D
j
) + (λ
N
j
D
j
− λ
P
j
D
j
)
,
R(a
B
j
|[x]
B
) ≤ R(a
P
j
|[x]
B
) ⇐⇒ Pr(D
j
|[x]
B
) ≤
(λ
P
j
D
j
− λ
B
j
D
j
)
(λ
P
j
D
j
− λ
B
j
D
j
) + (λ
B
j
D
j
− λ
P
j
D
j
)
,
R(a
B
j
|[x]
B
) ≤ R(a
N
j
|[x]
B
) ⇐⇒ Pr(D
j
|[x]
B
) ≥
(λ
B
j
D
j
− λ
N
j
D
j
)
(λ
B
j
D
j
− λ
N
j
D
j
) + (λ
N
j
D
j
− λ
B
j
D
j
)
,
R(a
N
j
|[x]
B
) ≤ R(a
P
j
|[x]
B
) ⇐⇒ Pr(D
j
|[x]
B
) ≤
(λ
P
j
D
j
− λ
N
j
D
j
)
(λ
P
j
D
j
− λ
N
j
D
j
) + (λ
N
j
D
j
− λ
P
j
D
j
)
,
R(a
N
j
|[x]
B
) ≤ R(a
B
j
|[x]
B
) ⇐⇒ Pr(D
j
|[x]
B
) ≤
(λ
B
j
D
j
− λ
N
j
D
j
)
(λ
B
j
D
j
− λ
N
j
D
j
) + (λ
N
j
D
j
− λ
B
j
D
j
)
.
By introducing three parameters α
j
, β
j
, and γ
j
:
α
j
=
(λ
P
j
D
j
− λ
B
j
D
j
)
(λ
P
j
D
j
− λ
B
j
D
j
) + (λ
B
j
D
j
− λ
P
j
D
j
)
,
β
j
=
(λ
B
j
D
j
− λ
N
j
D
j
)
(λ
B
j
D
j
− λ
N
j
D
j
) + (λ
N
j
D
j
− λ
B
j
D
j
)
,
γ
j
=
(λ
P
j
D
j
− λ
N
j
D
j
)
(λ
P
j
D
j
− λ
N
j
D
j
) + (λ
N
j
D
j
− λ
P
j
D
j
)
,
(3)
the decision rules (P)–(N) can be re-expressed as follows:
(P) If Pr(D
j
|[x]
B
) ≥ α
j
and Pr(D
j
|[x]
B
) ≥ γ
j
, decide x ∈ POS(D
j
|π
B
);
(
B) If Pr(D
j
|[x]
B
) ≤ α
j
and Pr(D
j
|[x]
B
) ≥ β
j
, decide x ∈ BND(D
j
|π
B
);
(
N) If Pr(D
j
|[x]
B
) ≤ β
j
and Pr(D
j
|[x]
B
) ≤ γ
j
, decide x ∈ NEG(D
j
|π
B
).
The conditions of rule (B) suggest that α
j
>β
j
may be a reasonable condition so that the boundary region may be
nonempty. By setting α
j
>β
j
, we obtain the following condition on the loss function:
(C2)
(λ
N
j
D
j
− λ
B
j
D
j
)
(λ
B
j
D
j
− λ
N
j
D
j
)
>
(λ
B
j
D
j
− λ
P
j
D
j
)
(λ
P
j
D
j
− λ
B
j
D
j
)
.
Conditions (C1) and (C2) imply that 1 ≥ α
j
> γ
j
>β
j
≥ 0. After tie breaking, the following simplified rules are obtained:
(P) If Pr(D
j
|[x]
B
) ≥ α
j
, decide x ∈ POS(D
j
|π
B
);
(
B) If β
j
< Pr(D
j
|[x]
B
)<α
j
, decide x ∈ BND(D
j
|π
B
);
(
N) If Pr(D
j
|[x]
B
) ≤ β
j
, decide x ∈ NEG(D
j
|π
B
).
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