The Scientific World Journal

Volume 2014 (2014), Article ID 348683, 13 pages

http://dx.doi.org/10.1155/2014/348683

## Rough Atanassov’s Intuitionistic Fuzzy Sets Model over Two Universes and Its Applications

School of Mathematics and Statistics, Chongqing University of Technology, Chongqing 400054, China

Received 26 August 2013; Accepted 18 November 2013; Published 13 May 2014

Academic Editors: E. Haghverdi, M. Mansour, and H. Xu

Copyright © 2014 Shuqun Luo and Weihua Xu. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

Recently, much attention has been given to the rough set models based on two universes. And many rough set models based on two universes have been developed from different points of view. In this paper, a novel model, that is, rough Atanassov’s intuitionistic fuzzy sets model over two different universes, is firstly proposed from Atanassov’s intuitionistic point of view. We study some important properties of approximation operators and investigate the rough degree in the novel model. Furthermore, an illustrated example is employed to demonstrate the conceptual arguments of the model. Finally, rough Atanassov’s intuitionistic fuzzy sets approach to decision is presented in the generalized approximation space over two universes by considering the problem about how to arrange patients to see the doctor reasonably, from which it can be found that the method is valuable and useful in real life.

#### 1. Introduction

Rough set theory, originally proposed by Pawlak in the early 1980s [1–3] as a useful tool for treating with uncertainty or imprecision information, has been successfully applied in the fields of artificial intelligence, pattern recognition, medical diagnosis, data mining, conflict analysis, algebra [4–12], and so on. In recent years, the rough set theory has aroused a great deal of interest among more and more researchers.

It is widely accepted that the theory of rough sets, which is very important to construct a pair of upper and lower approximation operators, is based on available information. In the Pawlak approximation space, the lower and upper approximations of arbitrary subset of the universe of discourse can be represented directly. The lower approximation is the union of all equivalence classes, which are classes induced by the equivalence relation on the universe and included in the given set. The upper approximation is the union of all equivalence classes, which are classes induced by the equivalence relation on the universe having a nonempty intersection with the given set. So, the equivalence relation is a key and primitive notion in Pawlak’s rough set model.

In the Pawlak approximation space, the equivalence relation is a very restrictive condition and the sets used are classical sets, so the application domain of rough set model is narrowed. In 1986, Atanassov introduced the concept of Atanassov’s intuitionistic fuzzy sets. Atanassov’s intuitionistic fuzzy set was considered as a generalization of fuzzy set and had been found to be very useful to deal with vagueness. Atanassov thought that Atanassov’s intuitionistic fuzzy set was characterized by a pair of functions, the membership function and the nonmembership function valued in . The degrees of membership and nonmembership are independent. So, Atanassov’s intuitionistic fuzzy set is more suitable and precise to represent the essence of vagueness and is more useful than fuzzy set in dealing with imperfect information. Nowadays, many excellent works over single universe have been achieved. For example, Zhou and Wu [13] presented the rough approximations of Atanassov’s intuitionistic fuzzy sets in crisp and fuzzy approximation spaces over single universe in which both constructive and axiomatic approaches are used. Zhang [14] generalized an interval-valued rough Atanassov’s intuitionistic fuzzy (IF) sets model by means of integrating the classical Pawlak rough set theory with interval-valued Atanassov’s intuitionistic fuzzy set theory. More excellent results can be found in [15, 16].

Moreover, the study on the rough set model over two universes was done, and it has become one of the hottest researches in recent years for authors. Shen and Wang [17] researched the variable precision rough set model over two universes and investigated the properties. Yan et al. [18] established the model of rough set over dual universes. Sun et al. [19] proposed Atanassov’s intuitionistic fuzzy rough set model over two universes with a constructive approach and discussed the basic properties of this model in fuzzy approximation space. More details about recent advancements of rough set model over two universes can be found in the literature [20–25]. In this paper, we will discuss rough Atanassov’s intuitionistic fuzzy sets model over two universes in the generalized approximation space, investigate its measures, and study how to use it for serving our life.

The rest of the paper is organized as follows. The next section reviews the basic concepts of Atanassov’s intuitionistic fuzzy sets, rough sets, and rough fuzzy sets. In the next section, rough Atanassov’s intuitionistic fuzzy sets model is constructed in generalized approximation space over two universes. Moreover, rough Atanassov’s intuitionistic fuzzy sets’ cut sets and some important properties are presented. In Section 4, we mainly studied how to measure the uncertainty of rough Atanassov’s intuitionistic fuzzy set over two universes. What is more, a general approach to decision making is established based on rough Atanassov’s intuitionistic fuzzy sets over two universes with a problem of how to order the patients to see the doctor reasonably as the background for the application in Section 5. Finally, we draw brief conclusions and set further research directions in Section 6.

#### 2. Preliminaries

In this section, we will review some necessary definitions and concepts required in the sequel of this paper.

##### 2.1. Atanassov’s Intuitionistic Fuzzy Sets

*Definition 1 (see [26, 27]). *Let be a nonempty finite set. Atanassov’s intuitionistic fuzzy set on is an object having the form
where and satisfy for all .

and are, respectively, called the degrees of membership and nonmembership of the element to .

The complement of Atanassov’s intuitionistic fuzzy set is denoted by .

Let denote the family of all Atanassov’s intuitionistic fuzzy sets on .

For any , some basic operations on are defined as follows:(1), for all ,(2), for all ,(3),(4),(5)if , then .

*Definition 2. *Let be Atanassov’s intuitionistic fuzzy set over and , , and the -level cut set of , denoted by , is defined as follows:
and are, respectively, called the -level cut set and the strong -level cut set of membership generated by . And and are, respectively, referred to as the -level cut set and the strong -level cut set of nonmembership generated by .

What is more, other types of cut sets and strong cut sets of Atanassov’s intuitionistic fuzzy set are denoted, for example, , which is called the -level cut set of .

##### 2.2. Fuzzy Rough Sets Model

*Definition 3 (see [28]). *Let be a fuzzy approximation space and be a fuzzy subset of . The lower approximation and upper approximation are denoted by and , respectively. The memberships of to are defined as
where “” and “” mean “min” and “max” operators, respectively, and is the membership of with respect to . The pair is called a fuzzy rough set.

##### 2.3. Rough Atanassov’s Intuitionistic Fuzzy Sets Model over One Universe

*Definition 4 (see [13]). *Let be a generalized approximation space, for any . The upper and lower approximations of , denoted by and , are, respectively, defined as follows:
where
where “” and “” mean “min” and “max” operators, respectively, and , are the membership and nonmembership of with respect to . The pair is called a fuzzy rough set in a generalized approximation space.

##### 2.4. Rough Fuzzy Sets Model over Two Universes

*Definition 5 (see [29]). *Let be a generalized approximation space over two universes, and for any , , denote
Then, and are called the lower and upper approximations of fuzzy set in , and and are called the lower and upper approximations of fuzzy set in , respectively. () and () are called rough fuzzy sets in generalized approximation space over two universes.

#### 3. Rough Atanassov’s Intuitionistic Fuzzy Sets Model over Two Universes

In this section, we will introduce rough Atanassov’s intuitionistic fuzzy sets model over the different universes and discuss some important properties of rough Atanassov’s intuitionistic fuzzy sets.

##### 3.1. Construction of Rough Atanassov’s Intuitionistic Fuzzy Sets

Let be nonempty finite universes, and a subset (i.e., : ) is called a binary relation from to .

In general, if , is called the binary relation over single universe. If satisfies reflexivity, symmetry, and transitivity, then we say is an equivalence relation. But in generalized approximation space over two universes, is a binary relation from to and then must not be equivalence relation.

*Definition 6 (see [22]). *Let be a crisp binary relation on the universes and . Then,(1) is serial if, for any , there exists , s.t. ,(2) is reverse serial if, for any , there exists , s.t. .

*Definition 7. *Let be a generalized approximation space over two universes, and for any , , denote
where
Then, and are called the lower and upper approximations of Atanassov’s intuitionistic fuzzy set in , and and are called the lower and upper approximations of Atanassov’s intuitionistic fuzzy set in . and are called rough Atanassov’s intuitionistic fuzzy sets over the universes and .

Furthermore, we also define the positive region , , negative region , , and boundary region , of about on the universe as follows, respectively:

If for any (resp., ), (resp., ), then Atanassov’s intuitionistic fuzzy set (resp., ) is Atanassov’s intuitionistic fuzzy definable set about the generalized approximation space . Otherwise, Atanassov’s intuitionistic fuzzy set (resp., ) is a rough set about the generalized approximation space over two universes.

*Example 8. *Let be a generalized approximation space over two universes. Let be two nonempty finite universes, and let denote the symptom set, and let denote the disease set. Suppose , , where each stands for one symptom, but each stands for a disease. Assume be a binary relation on , for any , if there exists , so the relation can be understood that if a person has a symptom , so he had possibly suffered from a disease .

Now, we can define the relation as follows:

From , we can see that is serial and reverse serial, and we can obtain

Suppose a person has the symptom conditions, and we can describe by Atanassov’s intuitionistic fuzzy set

By Definition 7, we can obtain

From the lower and upper approximations of , we can draw a conclusion that the person must have had the diseases , , , , at the degrees , , , , and , respectively. And the person may be have had the diseases , , , , at the degrees , , , , and , respectively.

*Remark 9. *In a generalized approximation space over two universes, we can find out that the lower and upper approximations of Atanassov’s intuitionistic fuzzy set belong to , and the lower and upper approximations of Atanassov’s intuitionistic fuzzy set belong to . This property is different from the lower and upper approximations over single universe. What is more, we can obtain other properties in the following.

##### 3.2. Corresponding Properties of Rough Atanassov’s Intuitionistic Fuzzy Sets

Theorem 10. *Let be a generalized approximation space over two universes, and for any , , one has the following properties:**, ;* *, ;**, ;* *, ;**;* *;**, ;* *, ;**, .*

*Proof. *We only need to prove the first part of each property as the similarity of the above properties.

According to Definition 7, we can obtain
So, we can have .

The property can be proved similarly.

We can have

Hence, we can obtain .

According to the definitions of Atanassov’s intuitionistic fuzzy lower and fuzzy upper approximations, (3) holds.

It is easy to prove it by property (3).

For any , we can have

Therefore, .

*Definition 11. *Let be a generalized approximation space over two universes, and for any , , denote
where , , and are called the lower and upper approximation of on the universe and and are called the lower and upper approximations of on the universe .

*Example 12 (continued from Example 8). *Let and let ; then, we have , so the lower and upper approximations of can be presented as follows:

*Remark 13. *In Definition 7, we give the concepts of the lower approximation and upper approximation of about from the universe to . Similarly, we can also define the lower approximation and upper approximation of sets , , , , , , and about from the universe to . For example, we define the lower approximation and upper approximation of , about from the universe to as follows:

*In the following discussion, without loss of generality, we only investigate the properties of , and , . The corresponding properties can be extended to the other lower approximations and upper approximations; here, we will not list them one by one.*

*Theorem 14. Let be a generalized approximation space over two universes; if , , one can obtain
*

*Proof. *Since , , so . For any , we can have . Thus, that is, .

The properties , , and can be proved similarly.

*Example 15 (continued from Example 12). *Let , , , and ; then, we have , so the lower and upper approximations of can be obtained as follows:

Then, and hold.

*According to Definition 7, we can define two pairs of Atanassov’s intuitionistic fuzzy sets as follows:
where
*

*Then, we can obtain the following properties.*

*Theorem 16. Let be a generalized approximation space over two universes, and for any , , then
*

*Proof. *For any , denote

Let , satisfy , if , then , and , . So, , ; therefore; , .

On the other hand, for any , , according to the definitions of , , we can know that there exists , s.t. ; that is, , ; thus, , , by the arbitrary of and , and we can obtain , . Hence, .

The properties , , and can be proved similarly.

*Definition 17. *Let be a generalized approximation space over two universes, , . If , then and are called lower rough equivalences of , denoted by . If , then and are called upper rough equivalences of , denoted by . If and , then and are called rough equivalences of , denoted by . If , then and are called lower rough equivalences of , denoted by . If , then and are called upper rough equivalences of , denoted by . If and , then and are called rough equivalences of , denoted by .

*Proposition 18. Let be a generalized approximation space over two universes, , ; then,(1), ; , .(2), ; , .(3) If , , then ; if , , then ; if , , then ; if , , then .(4) If or , then ; if or , then .(5) If or , then ; if or , then .(6) If and , then ; if and , then .(7) If and , then ; if and , then .*

*Proof. *Straightforward.

*Theorem 19. Let be a generalized approximation space over two universes, , ; then,(1), ;(2), .*

*Proof. *We can obtain them according to Proposition 18.

*Theorem 20. Let be a generalized approximation space over two universes, , for any , and if is a reverse serial relation on , denote
Then,(1), ,(2), .*

*Proof. * For any for any , , , , and . Thus, we can have .

The properties can be proved similarly.

(2) Since , , we can have that for any , , and . Therefore, .

*Theorem 21. Let be a generalized approximation space over two universes, , for any , and if is a serial relation on , denote
Then,(1), ,(2), .*

*Proof. *The proof is similar to Theorem 20.

*4. The Measures of Rough Atanassov’s Intuitionistic Fuzzy Sets Model over Two Universes*

*4. The Measures of Rough Atanassov’s Intuitionistic Fuzzy Sets Model over Two Universes**In this section, we will research some measures of rough Atanassov’s intuitionistic fuzzy set over different universes.*

*Definition 22. *Let be a generalized approximation space over two universes, , for any , , and the approximate precision of about can be defined as follows:
where and the notation denotes the cardinality of set.

*Let , and is called the rough degree of about the universe .*

*Theorem 23. Let be a generalized approximation space over two universes, , for any , , and the approximate precision and the rough degree satisfy the properties as follows:
*

*Proof. *According to Definition 22, this theorem can be proved easily.

*Example 24 (continued from Example 8). *We can find the -level cut set of and the -level cut set of as follows:

So, we can compute the approximation precision and rough degree as follows:

*Theorem 25. Let be a generalized approximation space over two universes, , , , and , for any , ; then,
*

*Proof. *Since , we can have . On the other hand, . Therefore, the theorem can be proved by Definition 22.

*Theorem 26. Let be a generalized approximation space over two universes, , , , for any , ; then,
*

*Proof. *The proof is similar to Theorem 25.

*Theorem 27. Let , and if , for any , , one can have
*

*Proof. *It can be proved by Theorem 25 and Definition 22.

*Theorem 28. Let , be two nonempty finite universes, and let be the relation of . For any , . The rough degrees and precisions of , , , and have the following relations. Consider
*

*Proof. *According to Theorem 10, we can obtain
On the other hand,
For classical sets and , we have
Hence,