Group Decision Making in Information Systems Security Assessment Using Dual Hesitant Fuzzy Set Dejian Yu,1,∗ José M. Merigó,2,3 Yejun Xu4 1 School of Information, Zhejiang University of Finance and Economics, Hangzhou, Zhejiang 310018, People’s Republic of China 2 Manchester Business School, University of Manchester, M15 6PB Manchester, UK 3 Department of Management Control and Information Systems, School of Economics and Business, University of Chile, 8330015 Santiago, Chile 4 Business School, Hohai University, Jiangning, Nanjing, Jiangsu 211100, People’s Republic of China Network information system security has become a global issue since it is related to the economic development and national security. Information system security assessment plays an important role in the development of security solutions. Aiming at this issue, a dual hesitant fuzzy (DHF) group decision-making (GDM) method was proposed in this paper to assist the assessment of network information system security. A systemic index containing four aspects was established including organization security, management security, technical security, and personnel management security. The DHF group evaluation matrix was constructed based on the individual evaluation information from each expert. Some power average operator–based DHF information aggregation operators are proposed and used to fusion the performance of each criterion for information systems. The advantage of these operators is that they can describe the relationship between the indexes quantitatively. Finally, a case study about information systems security assessment was C 2016 Wiley Periodicals, Inc. presented to verify the effectiveness of proposed GDM methods. 1. INTRODUCTION Since Torra and Narukawa1 and Torra2 proposed the hesitant fuzzy set (HFS), many extensions have been appeared to describe the vagueness of our subjective world. For example, Rodrı́guez et al.3 introduced the hesitant fuzzy linguistic term set. Interval-valued HFS was first presented by Chen et al.,4 it is characterized by the membership degrees were expressed by a set of possible intervals, is another extension of HFS. Qian et al.5 proposed the concept of generalized HFS by combine ∗ Author to whom all correspondence should be addressed; [email protected] INTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, VOL. 31, 786–812 (2016) C 2016 Wiley Periodicals, Inc. View this article online at wileyonlinelibrary.com. • DOI 10.1002/int.21804 GROUP DECISION MAKING IN INFORMATION SYSTEMS SECURITY 787 HFS with intuitionistic fuzzy set.6 Yu7 using the triangular fuzzy numbers rather than determined numbers to express the membership degree and proposed the triangular fuzzy HFS, based on which, a new decision-making method is proposed for a teaching quality evaluation problem. Yang et al.8 introduced the hesitant fuzzy rough set by combing the HFS and rough set. Zhu et al.9 proposed the dual HFS (DHFS) by adding the nonmembership degree to HFS. The DHFS was acknowledged as one of the effective mathematical means for investigating vagueness, uncertain, and incomplete information.10 For example, the review of a Ph.D. thesis in China is always taken by three experts anonymously, and the experts cannot exchange ideas. Owing to the complexity of reviewing a Ph.D. thesis, it is very hard for an expert to give exact evaluating values. The first expert thinks that the possibility of the Ph.D. thesis meeting the requirement is 0.6 and the possibility of the Ph.D. thesis does not meeting the requirement is 0.2. The second expert thinks that the possibility of the Ph.D. thesis meeting the requirement is 0.7 and the possibility of the Ph.D. thesis does not meeting the requirement is 0.2. The third expert thinks that the possibility of the Ph.D. thesis meeting the requirement is 0.8 and the possibility of the PhD thesis does not meeting the requirement is 0.1. In this situation, the evaluation information provided by three experts for the Ph.D. thesis can be expressed by a dual hesitant fuzzy element (DHFE){{0.6, 0.7, 0.8}, {0.1, 0.2}}. Therefore, it is far better for expressing the above phenomenon using DHFS than the HFS. DHFS has been received extensive attentions from scholars in recent years. Wang et al.11 defined the correlation measures for DHFS, based on which a clustering algorithm was also studied for DHFS and applied it to the issue of diamond evaluation and classification. Farhadinia12 studied the correlation coefficients of DHFS and interval-valued DHFS. Ye13 studied the decision-making method based on DHFS and correlation coefficient. Zhu and Xu (2013)14 developed typical DHFS and introduced the operations to improve the DHFS theory. DHF information aggregation is an interesting research area, which is also an object of study of DHFS. Some aggregation operators have been proposed to aggregate DHF information, such as DHF-weighted averaging, DHF-weighted geometric, DHF-ordered weighted averaging, DHF-ordered weighted geometric, DHFHA, and DHFHG operators.15 Ju et al.16 proposed some aggregation operators for aggregating interval-valued DHF information. The above aggregation operators for DHF information and interval-valued DHF information are with the assumption that the aggregated data are independent. However, in real situation, the aggregated data may correlate between each other.7,17–20 Therefore, it is important to study some new approach which can deal with this issue. The power average (PA)21 and the power geometric (PG)22 operators are two aggregation operators, which can deal with the correlation phenomenon between aggregated arguments. The PA and PG operators have been studied by many researchers and achieved many research results. The development of the power operators is summarized in Figure 1. We could see that the research about power operator is quite extensive. However, despite current research achievements on power operator, there are still some unsolved issues to be explored. To extend the power International Journal of Intelligent Systems DOI 10.1002/int 788 YU, MERIGÓ, AND XU Figure 1. The main development of power operator. operator to DHF and interval-valued DHF environment could enhance the research about power operator theory. First of all, we develop some aggregation operators for aggregating DHF and interval-valued DHF information based on power operator. Furthermore, we pay our attention to the GDM method using DHF information. The problem about information systems security assessment is investigated in this paper based on the proposed GDM method. The remainder of this paper is set as follows. In Section 2, we briefly review basic concepts of DHFS, interval-valued dual DHFS, and power operators. In Section 3, we present some new power operators for aggregating DHF information. Section 4 presents some new power operators for aggregating interval-valued DHF information. In Section 6, we present a GDM method using DHF information; the real case about information systems security assessment is presented in this section. The conclusions are discussed in Section 6. 2. SOME BASIC CONCEPTS The DHFS was defined by Zhu et al.9 as follows: DEFINITION 1. Suppose there is a fixed set X. A DHFS D on the fixed set X is described as follows. D = {x, h(x), g(x)|x ∈ X}. International Journal of Intelligent Systems DOI 10.1002/int (1) GROUP DECISION MAKING IN INFORMATION SYSTEMS SECURITY 789 The h(x) and g(x) are expressed by several possible determined numbers and indicated the membership degree and nonmembership degree, respectively.9 Zhu et al.9 introduced the comparative laws for any two DHFEs. DEFINITION 2. Suppose there are two DHFEs d1 = (h1 , g1 ) and d2 = (h2 , g2 ). The scores functions of the two DHFEs are defined as follows: S(d1 ) = 1 1 γ1 − η1 , #h1 γ ∈h #g1 η ∈g (2) 1 1 γ2 − η2 . #h2 γ ∈h #g2 η ∈g (3) 1 S(d2 ) = 2 1 2 1 1 2 2 If S(d1 ) > S(d2 ), then d1 d2 . Example 1 illustrates the comparative laws described above. Example 1. Let d1 = {{0.2, 0.3}, {0.4, 0.7}}, d2 = {{0.2, 0.6}, {0.2}}, and d3 = {{0.5}, {0.4, 0.5}}, be three DHFEs. We can get the scores of three DHFEs according to Definition 2. 1 1 (0.2 + 0.3) − (0.4 + 0.7) = −0.3, 2 2 1 1 S(d2 ) = (0.2 + 0.6) − (0.2) = 0.2, 2 1 1 1 S(d3 ) = (0.5) − (0.4 + 0.5) = 0.05. 1 2 S(d1 ) = Since S(d2 ) > S(d3 ) > S(d1 ), We have d2 d3 d1 . DEFINITION 3. Let d, d1 , and d2 be three DHFEs, Then (1) (2) (3) (4) d1 ⊕ d2 = ∪γ1 ∈h1 ,γ2 ∈h2 ,η1 ∈g1 ,η2 ∈g2 {{γ1 + γ2 − γ1 γ2 }, {η1 η2 }}, d1 ⊗ d2 = ∪γ1 ∈h1 ,γ2 ∈h2 ,η1 ∈g1 ,η2 ∈g2 {{γ1 γ2 }, {η1 + η2 − η1 η2 }}, nd = ∪γ ∈h,η∈g {{1 − (1 − γ )n }, {ηn }}, d n = ∪γ ∈h,η∈g {{γ n }, {1 − (1 − η)n }}. Farhadinia3 extended the DHFS to a more generalized form and introduced the concept of interval-valued DHFS (IVDHFS). The definition of IVDHFS is defined as follows: International Journal of Intelligent Systems DOI 10.1002/int 790 YU, MERIGÓ, AND XU DEFINITION 4. Suppose there is a fixed set X. A IVDHFS on the fixed set X is described as follows: = {x, h̃(x), g̃(x)|x ∈ X}. (4) The h̃(x) and g̃(x) are expressed by several possible intervals of real numbers and indicated the membership degree range and nonmembership degree range, respectively. DEFINITION 5. Suppose there are two IVDHFEs d˜1 = (h̃1 , g̃1 ) and d˜2 = (h̃2 , g̃2 ). The scores functions of the two IVDHFEs are defined as follows: S(d˜1 ) = 1 1 γ̃1 − η̃1 #g̃1 η̃ ∈g̃ #h̃1 γ̃1 ∈h̃1 1 1 1 γ̃1L + γ̃1U 1 η̃1L + η̃1U = − , 2 #g̃1 η̃ ∈g̃ 2 #h̃1 γ̃1 ∈h̃1 S(d˜2 ) = 1 (5) 1 1 1 γ̃2 − η̃2 #g̃2 η̃ ∈g̃ #h̃2 γ̃2 ∈h̃2 2 2 1 η̃2L + η̃2U 1 γ̃2L + γ̃2U − . = 2 #g̃2 η̃ ∈g̃ 2 #h̃2 γ̃2 ∈h̃2 2 (6) 2 If S(d˜1 ) > S(d˜2 ), then d˜1 d˜2 . Example 2 illustrates the comparative laws described above. In Equations (5) and (6), L and U are the lower and upper bounds of intervals of real numbers, respectively. Example 2. Let d˜1 = {{[0.2, 0.3], [0.3, 0.4], [0.2, 0.5]}, {[0.1, 0.2], [0.2, 0.5]}}, and d̃3 = {{[0.1, 0.2]}, d˜2 = {{[0.2, 0.3], [0.5, 0.6]}, {[0.1, 0.2], [0.2, 0.3]}}, {[0.3, 0.4], [0.1, 0.3]}}, be three IVDHFEs. We can get the scores of three IVDHFEs according to Definition 5. 0.2 + 0.3 0.3 + 0.4 0.2 + 0.5 + + 2 2 2 1 0.1 + 0.2 0.2 + 0.5 − + = 0.0667, 2 2 2 1 0.1 + 0.2 0.2 + 0.3 1 0.2 + 0.3 0.5 + 0.6 S(d˜2 ) = + − + = 0.2, 2 2 2 2 2 2 1 0.3 + 0.4 0.1 + 0.3 0.1 + 0.2 − + = −0.125. S(d˜3 ) = 2 2 2 2 S(d˜1 ) = 1 3 International Journal of Intelligent Systems DOI 10.1002/int GROUP DECISION MAKING IN INFORMATION SYSTEMS SECURITY 791 Since S(d˜2 ) > S(d˜1 ) > S(d̃3 ), We have d˜2 d˜1 d̃3 . In the following, we define the operations for IVDHFEs; it is very important for the rest of this paper. DEFINITION 6. Let d̃, d˜1 and d˜2 be three IVDHFEs, Then (1) d˜1 ⊕ d˜2 = ∪γ̃1 ∈h̃1 ,γ̃2 ∈h̃2 ,η̃1 ∈g̃1 ,η̃2 ∈g̃2 {{[γ̃1L + γ̃2L − γ̃1L γ̃2L , γ̃1U + γ̃2U − γ̃1U γ̃2U ]}, {[η̃1L η̃2L , η̃1U η̃2U ]}}, (2) d˜1 ⊗ d˜2 = ∪γ̃1 ∈h̃1 ,γ̃2 ∈h̃2 ,η̃1 ∈g̃1 ,η̃2 ∈g̃2 {{[γ̃1L γ̃2L , γ̃1U γ̃2U ]}, {[η̃1L + η̃2L − η̃1L η̃2L , η̃1U + η̃2U − η̃1U η̃2U ]}}, n n n n (3) nd̃ = ∪γ̃ ∈h̃,η̃∈g̃ {{[1 − (1 − γ̃ L ) , 1 − (1 − γ̃ U ) ]}, {[(η̃L ) , (η̃U ) ]}}, n L n U n L n U n (4) d̃ = ∪γ̃ ∈h̃,η̃∈g̃ {{[(γ̃ ) , (γ̃ ) ]}, {[1 − (1 − η̃ ) , 1 − (1 − η̃ ) ]}}. Yager21 introduced the PA operator to aggregate a collection of data ai (i = 1, 2, . . . , n), defined as follows: n (1 + T (ai ))ai P A(a1 , a2 , . . . , an ) = i=1 n i=1 (1 + T (ai )) (7) where T (ai ) = nj=1,j =i sup(ai , aj ) and sup(ai , aj ) is the support for ai from aj , which satisfies the following conditions:23 (1) Sup(ai , aj ) ∈ [0, 1]; (2) Sup(ai , aj ) = Sup(aj , ai ); (3) Sup(ai , aj ) ≥ Sup(as , at ), if d(ai , aj ) < d(as , at ). Xu and Yager22 defined a PG operator as follows:. P G(a1 , a2 , . . . , an ) = n ai n (1+T (ai )) i=1 n (1+T (a )) i i=1 (8) i=1 3. DHF POWER AGGREGATION OPERATORS In this section, we first propose the distance measures for the DHFEs. Then, we propose the DHF power weighted average (DHFPWA) operator and the DHF power–weighted geometric (DHFPWG) operator. Next, we suggest the generalized DHF power–weighted average (GDHFPWA) operator and the generalized DHF power–weighted geometric (GDHFPWG) operator. International Journal of Intelligent Systems DOI 10.1002/int 792 YU, MERIGÓ, AND XU 3.1. Distance Measures for DHFES Motivated by the distance measure of HFS studied by Xu and Xia24 and distance measure of Intuitionistic fuzzy set (IFS), we define some distance measure for DHFEs. DEFINITION 7. For two DHFEs d1 = (h1 , g1 ) and d2 = (h2 , g2 ), the distance measure between d1 and d2 , denoted as d(d1 , d2 ), d(d1 , d2 ) = l 2 1 ρ(i) ρ(i) h1 − h2 l i=1 1/2 l 2 1 ρ(i) ρ(i) + g1 − g2 s i=1 1/2 (9) . In Equation (9), l(h1 ) means the number of elements in h1 and l = max{l(h1 ), l(h2 )}. Similarly, s(g1 ) and s = max{s(g1 ), l(g2 )} have corresponding meanings. Example 3. Let d1 = (h1 , g1 ) = {{0.1, 0.2, 0.3}, {0.4, 0.5}} and d2 = (h2 , g2 ) = {{0.3, 0.6}, {0.2}} be two DHFEs. In the following, we calculate the distance of these two DHFEs was given as follows: Since there are three elements in h1 and only two elements in h2 , therefore, we add the minimum value in h2 to h2 , in other words, we add 0.3 to h2 . Similarly, we add 0.2 to g2 . According to Equation (9), we have 1/λ 1 2 2 2 (0.1 − 0.3) + (0.2 − 0.3) + (0.3 − 0.6) d(d1 , d2 ) = 3 1/λ 1 2 2 (0.4 − 0.2) + (0.5 − 0.2) + = 0.4710. 2 3.2. DHF Power Information Aggregation Operators In the following, we study the power operators under DHF environment. DEFINITION 8. Let dj (j = 1, 2, . . . , n) be a collection of DHFEs, and w = (w1 , w2 , . . . , wn )T be the standardized weight vector of dj (j = 1, 2, . . . , n), then the DHFPWA operator is defined as follows: DHFPWA (d1 , d2 , . . . , dn ) = (w1 (1 + T (d1 ))) d1 ⊕ (w2 (1 + T (d2 ))) d2 ⊕ · · · ⊕ (wn (1 + T (dn ))) dn n j =1 wj (1 + T (dj )) (10) International Journal of Intelligent Systems DOI 10.1002/int GROUP DECISION MAKING IN INFORMATION SYSTEMS SECURITY 793 where n T (dj ) = j = 1, 2, . . . , n wi sup(di , dj ), (11) i=1,i=j Sup(di , dj ) = 1 − d(di , dj ) is the support for di from dj , d is a distance measure. Especially, if w = ( n1 , n1 , . . . , n1 )T , then the DHFPWA reduces to an DHF power average (DHFPA) operator: DHFPA (d1 , d2 , . . . , dn ) = (1 + T (d1 )) d1 ⊕ (1 + T (d2 )) d2 ⊕ · · · ⊕ (1 + T (dn )) dn n j =1 (1 + T (dj )) (12) n 1 sup(di , dj ), T (dj ) = n i=1,i=j (13) where j = 1, 2, . . . , n Motivated by the idea of the PG operator, we define the DHFPWG operator as follows: DEFINITION 9. Let dj (j = 1, 2, . . . , n) be a collection of DHFEs, and w = (w1 , w2 , . . . , wn )T be the standardized weight vector of dj (j = 1, 2, . . . , n), then the DHFPWG operator is defined as follows: DHFPWG (d1 , d2 , . . . , dn ) = (d1 ) w (1+T (d1 )) n 1 j =1 wj (1+T (dj )) ⊗ (d2 ) w (1+T (d2 )) n 2 j =1 wj (1+T (dj )) ⊗ · · · ⊗ (dn ) nwn (1+T (dn )) j =1 wj (1+T (dj )) (14) where T (dj ) = n wi sup(di , dj ), j = 1, 2, . . . , n (15) i=1,i=j Sup(di , dj ) = 1−d(di , dj ) is the support for di from dj , d is a distance measure. Especially, if w = ( n1 , n1 , . . . , n1 )T , then the DHFPWG reduces to a DHF power geometric (DHFPG) operator: DHFPG (d1 , d2 , . . . , dn ) = (d1 ) 1+T (d1 ) n j =1 (1+T (dj )) ⊗ (d2 ) 1+T (d2 ) n j =1 (1+T (dj )) ⊗ · · · ⊗ (dn ) International Journal of Intelligent Systems n 1+T (dn ) j =1 (1+T (dj )) DOI 10.1002/int (16) 794 YU, MERIGÓ, AND XU where T (dj ) = n 1 sup(di , dj ), n i=1,i=j j = 1, 2, . . . , n (17) We can drive Theorem 1 based on the operation laws of DHFEs and Definitions 8 and 9. THEOREM 1. Let dj (j = 1, 2, . . . , n) be a collection of DHFEs and w = (w1 , w2 , . . . , wn )T be the standardized weight vector of dj (j = 1, 2, . . . , n), then, their aggregated value by using the DHFPWA or DHFPWG operator is also an DHFE, and DHFPWA A(d1 , d2 , . . . , dn ) w (1+T (dj )) w (1+T (dj )) n j n j n n wj (1+T (dj )) wj (1+T (dj )) j =1 j =1 1 − (1 − γj ) , (ηj ) = ∪γj ∈hj , ηj ∈gj j =1 j =1 (18) DHFPWG (d1 , d2 , . . . , dn ) w (1+T (dj )) w (1+T (dj )) n j n j n n w (1+T (dj )) , 1 − (1 − ηj ) j =1 wj (1+T (dj )) = ∪γj ∈hj , ηj ∈gj (γj ) j =1 j j =1 j =1 (19) Example 4. Let d1 = (h1 , g1 ) = {{0.1, 0.2, 0.3}, {0.4, 0.5}}, d2 = (h2 , g2 ) = {{0.3, 0.6}, {0.2}}, and d3 = {{0.5}, {0.3, 0.5}} be three DHFEs. and w = (0.24, 0.45, 0.31)T be the standardized weight vector of dj (j = 1, 2, 3), In the following, we first calculate the distances between the three DHFEs. 1/λ 1 2 2 2 (0.1 − 0.3) + (0.2 − 0.3) + (0.3 − 0.6) d(d1 , d2 ) = 3 1/λ 1 (0.4 − 0.2)2 + (0.5 − 0.2)2 + = 0.4710, 2 1/λ 1 (0.1 − 0.5)2 + (0.2 − 0.5)2 + (0.3 − 0.5)2 d(d1 , d3 ) = 3 1/λ 1 (0.4 − 0.3)2 + (0.5 − 0.5)2 + = 0.3816, 2 1/λ 1 (0.3 − 0.5)2 + (0.6 − 0.5)2 d(d2 , d3 ) = 2 1/λ 1 (0.2 − 0.3)2 + (0.2 − 0.5)2 + = 0.2288. 2 International Journal of Intelligent Systems DOI 10.1002/int GROUP DECISION MAKING IN INFORMATION SYSTEMS SECURITY 795 Therefore, sup(d1 , d2 ) = 0.5290, sup(d1 , d3 ) = 0.6184, sup(d2 , d3 ) = 0.7712. and T (d1 ) = 0.4298, T (d2 ) = 0.3660, T (d3 ) = 0.4954. w1 (1 + T (d1 )) n = 0.2414, j =1 wj (1 + T (dj )) w2 (1 + T (d2 )) n = 0.4325, j =1 wj (1 + T (dj )) w3 (1 + T (d3 )) n = 0.3261. j =1 wj (1 + T (dj )) DHFPWA (d1 , d2 , . . . , dn ) = {{0.3335, 0.4768, 0.3522, 0.4915, 0.3727, 0.5076}, {0.2698, 0.3188, 0.2848, 0.3364}}, DHFPWG (d1 , d2 , . . . , dn ) = {{0.2718, 0.3668, 0.3213, 0.4337, 0.3544, 0.4783}, {0.2855, 0.3597, 0.3162, 0.3873}}. 3.3. Generalized DHF Power Information Aggregation Operators Based on the OWA operator,25 Yager26 proposed the generalized OWA (GOWA) operator. Based on the GOWA operator, some generalized power operators have been proposed.27 In this section, we study the generalized form of DHFPWA and DHFPWG operators and propose the GDHFPWA and GDHFPWG operators. DEFINITION 10. Let dj (j = 1, 2, . . . , n) be a collection of DHFEs, and w = (w1 , w2 , . . . , wn )T be the standardized weight vector of dj (j = 1, 2, . . . , n), then the GDHFPWA operator and the GDHFPWG operator are defined as follows: ⎞1/λ ⎛ n wj 1 + T (dj ) n djλ ⎠ , GDHFPWA (d1 , d2 , . . . , dn ) = ⎝ w (1 + T (d )) j j j =1 j =1 ⎛ ⎞ w 1+T (d ) n 1 ⎝ (nj=1j (wj (1+Tj (d))j )) ⎠ λdj GDHFPWA (d1 , d2 , . . . , dn ) = , λ j =1 International Journal of Intelligent Systems DOI 10.1002/int (20) (21) 796 YU, MERIGÓ, AND XU where λ ∈ (0, +∞), and T (dj ) = n wi sup(di , dj ), j = 1, 2, . . . , n (22) i=1,i=j Sup(d, dj ) = 1−d(di , dj ) is the support for di from dj , d is a distance measure. Especially, if λ = 1, then the GDHFPWA reduces to a DHFPWA operator proposed in Definition 8, and the GDHFPWG reduces to a DHFPWG operator proposed in Definition 9. THEOREM 2. Let dj (j = 1, 2, . . . , n) be a collection of DHFEs, and w = (w1 , w2 , . . . , wn )T be the standardized weight vector of dj (j = 1, 2, . . . , n), then their aggregated value by using the GDHFPWA operator or the GDHFPWG operator are also a DHFE, and GHFPWA (d1 , d2 , . . . , dn ) 1/λ w (1+T (dj )) j n λ nj=1 wj (1+T (dj )) = ∪γj ∈hj , ηj ∈gj 1 − (1 − γj ) , j =1 1/λ (dj )) nwj (1+T n w (1+T (d )) λ j j . 1− 1− 1−(1−ηj ) j =1 j =1 (23) GHFPWG (d1 , d2 , . . . , dn ) 1/λ (dj )) nwj (1+T n w (1+T (d )) λ j = ∪γj ∈hj , ηj ∈gj 1− 1− 1−(1−γj ) j =1 j , j =1 n 1 − (1 − j =1 ηjλ ) w (1+T (dj )) n j j =1 wj (1+T (dj )) 1/λ . (24) Example 5. Let d1 = (h1 , g1 ) = {{0.3, 0.4}, {0.1, 0.2, 0.4}}, d2 = (h2 , g2 ) = {{0.3, 0.4, 0.5}, {0.2}}, and d3 = {{0.4}, {0.1, 0.3}} be three DHFEs. and w = (0.31, 0.38, 0.31)T be the standardized weight vector of dj (j = 1, 2, 3), Then, 1/2 1 (0.3 − 0.3)2 + (0.3 − 0.4)2 + (0.4 − 0.5)2 3 1/2 1 2 2 2 (0.1 − 0.2) + (0.2 − 0.2) + (0.4 − 0.2) + = 0.2107 3 1/2 1 (0.3 − 0.4)2 + (0.4 − 0.4)2 d(d1 , d3 ) = 2 d(d1 , d2 ) = International Journal of Intelligent Systems DOI 10.1002/int GROUP DECISION MAKING IN INFORMATION SYSTEMS SECURITY 797 1/2 1 (0.1 − 0.1)2 + (0.2 − 0.1)2 + (0.4 − 0.3)2 3 1/2 1 (0.3 − 0.4)2 + (0.4 − 0.4)2 + (0.5 − 0.4)2 d(d2 , d3 ) = 3 1/2 1 2 2 (0.2 − 0.1) + (0.2 − 0.3) + = 0.1816. 2 + = 0.1524, Therefore, sup(d1 , d2 ) = 0.7893, sup(d1 , d3 ) = 0.8476, sup(d2 , d3 ) = 0.8184. and T (d1 ) = 0.6179, T (d2 ) = 0.4431, T (d3 ) = 0.5717. w1 (1 + T (d1 )) w2 (1 + T (d2 )) n = 0.3263, n = 0.3567, j =1 wj (1 + T (dj )) j =1 wj (1 + T (dj )) w3 (1 + T (d3 )) n = 0.3170. j =1 wj (1 + T (dj )) When λ = 1, then GDHFPWA (d1 , d2 , d3 ) = {{0.3334, 0.3690, 0.4088, 0.3661, 0.4000, 0.4378}, {0.1280, 0.1814, 0.1605, 0.2274, 0.2013, 0.2852}}, and its score equals 0.1885. GDHFPWG (d1 , d2 , d3 ) = {{0.3286, 0.3642, 0.3943, 0.3610, 0.4000, 0.4331}, {0.1370, 0.2031, 0.1696, 0.2332, 0.2440, 0.3019}}, and its score equals 0.1654. When λ = 5, then GDHFPWA (d1 , d2 , d3 ) = {{0.3453, 0.3778, 0.4332, 0.3755, 0.4000, 0.4467}, {0.1256, 0.1724, 0.1571, 0.2244, 0.1834, 0.2734}}, and its score equals 0.2070. GDHFPWG (d1 , d2 , d3 ) = {{0.3247, 0.3590, 0.3788, 0.3557, 0.4000, 0.4276}, {0.1645, 0.2453, 0.1859, 0.2507, 0.3222, 0.3353}}, and its score equals 0.1237. International Journal of Intelligent Systems DOI 10.1002/int 798 YU, MERIGÓ, AND XU Figure 2. Comparison between GDHFPWA and GDHFPWG (λ ∈ (0, 10)). When λ = 10, then GDHFPWA (d1 , d2 , d3 ) = {{0.3607, 0.3855, 0.4554, 0.3839, 0.4000, 0.4591}, {0.1223, 0.1611, 0.1520, 0.2203, 0.1657, 0.2585}}, and its score equals 0.2274. GDHFPWG (d1 , d2 , d3 ) = {{0.3196, 0.3506, 0.3599, 0.3473, 0.4000, 0.4209}, {0.1804, 0.2680, 0.1925, 0.2684, 0.3577, 0.3596}}, and its score equals 0.0953. Taking λ ∈ (0, 10), the comparison between GDHFPWA operator and GDHFPWG operator is shown in Figure 2. 4. INTERVAL-VALUED DHF POWER AGGREGATION OPERATORS Farhadinia3 extended the DHFS to a more generalized form and introduced the interval-valued DHFS (IVDHFS). In this section, we focus on the intervalvalued DHF information aggregation problem based on power operators. First of all, we give the definition of the distance measures for the IVDHFEs. Second, we propose some power operators for aggregating interval-valued DHF information; some generalized forms of these operators are also investigated. International Journal of Intelligent Systems DOI 10.1002/int 799 GROUP DECISION MAKING IN INFORMATION SYSTEMS SECURITY 4.1. Distance Measures for IVDHFEs In Section 3.1, we studied the distance measures of DHFS, based on which, we investigate the distance measures of IVDHFS. DEFINITION 11. For two IVDHFEs d˜1 = (h̃1 , g̃1 ) and d˜2 = (h̃2 , g̃2 ), the distance measure between d˜1 and d˜2 , is denoted as d(d˜1 , d˜2 ), d(d˜1 , d˜2 ) = l 2 1 ρ(i) ρ(i) − h̃ h̃ 2 l i=1 1 1/2 l 2 1 ρ(i) ρ(i) + − g̃ g̃ 2 s i=1 1 1/2 (25) In Equation (25), l(h̃1 ) means the number of elements in h̃1 and l = max{l(h̃1 ), l(h̃2 )}. If l(h̃1 ) < l(h̃2 ), then h̃1 should be extended by adding the minimum value in it until it has the same length with h̃2 .28 s(g̃1 ) and s = max{s(g̃1 ), l(g̃2 )} have corresponding meanings. Example 6. Let d˜1 = {{[0.1, 0.3], [0.3, 0.4], [0.2, 0.5]}, {[0.1, 0.2], [0.2, 0.5]}}, d˜2 = {{[0.2, 0.3], [0.5, 0.6]}, {[0.1, 0.2], [0.2, 0.3]}} be two IVDHFEs. In the following, we calculate the distance of these two IVDHFEs. According to Equation (25), we have 1/2 1 2 2 2 (0.1 − 0.2) + (0.2 − 0.2) + (0.3 − 0.5) d(d̃1 , d̃2 ) = 3 1/2 1 (0.3 − 0.3)2 + (0.4 − 0.3)2 + (0.5 − 0.6)2 + 3 1/2 1 2 2 (0.1 − 0.1) + (0.2 − 0.2) + 2 1/2 1 2 2 (0.2 − 0.2) + (0.5 − 0.3) + = 0.3522. 2 4.2. Interval-Valued DHF Power Information Aggregation Operators In this section, we study the power operators using interval-valued DHF information. DEFINITION 12. Let d˜j (j = 1, 2, . . . , n) be a collection of DHFEs, and w = (w1 , w2 , . . . , wn )T be the standardized weight vector of d˜j (j = 1, 2, . . . , n), then the interval-valued DHF power weighted average (IVDHFPWA) operator and interval-valued DHF power weighted geometric (IVDHFPWG) operator were International Journal of Intelligent Systems DOI 10.1002/int 800 YU, MERIGÓ, AND XU defined as follows: IVDHFPWA (d˜1 , d˜2 , . . . , d̃n ) w1 1 + T (d˜1 ) d˜1 ⊕ w2 1 + T (d̃2 ) d̃2 ⊕ · · · ⊕ wn 1 + T (d̃n ) d̃n , = n ˜ j =1 wj (1 + T (d j )) (26) IVDHFPWG (d˜1 , d˜2 , . . . , d˜n = (d˜1 ) w (1+T (d̃1 )) n 1 ˜ j =1 wj (1+T (d j )) ⊗ (d˜2 ) w (1+T (d̃2 )) n 2 ˜ j =1 wj (1+T (d j )) ⊗ · · · ⊗ (d˜n ) w (1+T (d̃n )) n n ˜ j =1 wj (1+T (d j )) . (27) where T (d˜j ) = n j = 1, 2, . . . , n. wi sup(d˜i , d˜j ), (28) i=1,i=j Sup(d˜i , d˜j ) = 1 − d(d˜i , d˜j ) is the support for d˜i from d˜j , d is a distance measure. Especially, if w = ( n1 , n1 , . . . , n1 )T , then the IVDHFPWA reduces to an intervalvalued DHF power average (IVDHFPA) operator: IVDHFPA (d˜1 , d˜2 , . . . , d˜n ) 1 + T (d̃1 ) d̃1 ⊕ 1 + T (d̃2 ) d̃2 ⊕ · · · ⊕ 1 + T (d̃n ) d̃n . = n ˜ j =1 (1 + T (d j )) (29) The IVDHFPWG reduces to an interval-valued DHF power geometric (IVDHFPG) operator: IVDHFPG (d˜1 , d˜2 , . . . , d˜n ) = (d˜1 ) 1+T (d̃1 ) n ˜ j =1 (1+T (d j )) ⊗ (d˜2 ) 1+T (d̃2 ) n ˜ j =1 (1+T (d j )) ⊗ · · · ⊗ (d˜n ) n 1+T (d̃n ) ˜ j =1 (1+T (d j )) , (30) where T (d˜j ) = n 1 sup(d˜i , d˜j ), n i=1,i=j j = 1, 2, . . . , n. (31) THEOREM 3. Let d˜j (j = 1, 2, . . . , n) be a collection of IVDHFEs, and w = (w1 , w2 , . . . , wn )T be the standardized weight vector of d˜j (j = 1, 2, . . . , n), then their aggregated value by using the IVDHFPWA or IVDHFPWG operator is also International Journal of Intelligent Systems DOI 10.1002/int 801 GROUP DECISION MAKING IN INFORMATION SYSTEMS SECURITY an IVDHFE, and IVDHFPWA (d˜1 , d˜2 , . . . , d˜n ) = ∪γ̃j ∈h̃j , η̃j ∈g̃j n × 1 − (1 − γ̃jL ) w (1+T (d˜j )) n j ˜ j =1 wj (1+T (d j )) j =1 n j =1 (η̃Lj ) w (1+T (d˜j )) n j ˜ j =1 wj (1+T (d j )) n , j =1 IVDHFPWG (d˜1 , d˜2 , . . . , d˜n ) = ∪γ̃j ∈h̃j , η̃j ∈g̃j n j =1 n 1 − (1 − η̃Lj ) (γ̃jL ) (η̃Uj ) , n 1 − (1 − γ̃jU ) w (1+T (d˜j )) n j ˜ j =1 wj (1+T (d j )) n , j =1 j =1 j =1 w (1+T (d˜j )) n j ˜ j =1 wj (1+T (d j )) w (1+T (d˜j )) n j ˜ j =1 wj (1+T (d j )) w (1+T (d˜j )) n j ˜ j =1 wj (1+T (d j )) n , (γ̃jU ) (32) w (1+T (d˜j )) n j ˜ j =1 wj (1+T (d j )) , 1 − (1 − η̃Uj ) w (1+T (d˜j )) n j ˜ j =1 wj (1+T (d j )) , j =1 (33) 4.3. Generalized Interval-Valued DHF Power Information Aggregation Operators In this section, we extend the IVDHFPWA and IVDHFPWG operators and propose the generalized IVDHFPWA and generalized IVDHFPWG operators. DEFINITION 13. Let d˜j (j = 1, 2, . . . , n) be a collection of IVDHFEs and w = (w1 , w2 , . . . , wn )T be the standardized weight vector of d˜j (j = 1, 2, . . . , n), then the generalized interval-valued DHF power weighted average (GIVDHFPWA) operator and the generalized interval-valued DHF power weighted geometric (GIVDHFPWG) operator are defined as follows: ⎛ GIVDHFPWA (d˜1 , d˜2 , . . . , d˜n ) = ⎝ n j =1 ⎞1/λ ˜ wj 1 + T (d j ) d˜λ ⎠ , (34) n wj (1 + T (d˜j )) j j =1 ⎛ ⎞ (d˜j ))) n (nwj (w1+T 1 ˜ GIVDHFPWG (d˜1 , d˜2 , . . . , d˜n ) = ⎝ λd˜j j =1 j (1+T (d j )) ⎠ , λ j =1 International Journal of Intelligent Systems DOI 10.1002/int (35) 802 YU, MERIGÓ, AND XU where λ ∈ (0, +∞), and n T (d˜j ) = j = 1, 2, . . . , n. wi sup(d˜i , d˜j ), (36) i=1,i=j Sup(d̃, d˜j ) = 1−d(d˜i , d˜j ) is the support for d˜i from d˜j , d is a distance measure. THEOREM 4. Let d˜j (j = 1, 2, . . . , n) be a collection of IVDHFEs and w = (w1 , w2 , . . . , wn )T be the standardized weight vector of d˜j (j = 1, 2, . . . , n), then their aggregated value by using the GIVDHFPWA operator or the GIVDHFPWG operator are also an IVDHFE, and GIVHFPWA (d˜1 , d˜2 , . . . , d˜n ) ⎧⎧⎡ 1/λ w (1+T (d˜ )) ⎨⎨ L λ nj=1j wj (1+Tj (d˜j )) n ⎣ 1 − 1 − γ̃j , = ∪γ̃j ∈h̃j , η̃j ∈g̃j ⎩⎩ j =1 w (1+T (d˜ )) λ nj=1j wj (1+Tj (d˜j )) 1 − 1 − γ̃jU n j =1 1/λ ⎤⎫ ⎬ ⎦ , ⎭ ⎧⎡ 1/λ (d˜j )) ⎨ nwj (1+T n ˜ )) w (1+T ( d L λ j ⎣1− 1− 1 − (1 − η̃j ) j =1 j , ⎩ j =1 nwj (1+T (d˜j ))˜ n U λ j =1 wj (1+T (d j )) 1 − 1− 1−(1−η̃j ) j =1 1/λ ⎤⎫⎫ ⎬⎬ ⎦ . ⎭⎭ (37) GIVHFPWG (d̃1 , d̃2 , . . . , d̃n ) ⎧⎧⎡ 1/λ ⎨⎨ wj (1+T (d˜j )) n λ nj=1 wj (1+T (d˜j )) L ⎣1 − 1− 1−(1−γ̃j ) , = ∪γ̃j ∈h̃j , η̃j ∈g̃j ⎩⎩ j =1 (d j )) nwj (1+T wj (1+T (d˜j )) U λ j =1 1 − 1− 1 − (1 − γ̃j ) ˜ n j =1 1/λ ⎤⎫ ⎬ ⎦ , ⎭ ⎧⎡ 1/λ w (1+T (d˜ )) ⎨ L λ nj=1j wj (1+Tj (d˜j )) n ⎣ 1 − 1 − η̃j , ⎩ j =1 w (1+T (d˜ )) U λ nj=1j wj (1+Tj (d˜j )) n 1 − 1 − η̃j j =1 1/λ ⎤⎫⎫ ⎬⎬ ⎦ . ⎭⎭ International Journal of Intelligent Systems DOI 10.1002/int (38) GROUP DECISION MAKING IN INFORMATION SYSTEMS SECURITY 803 Example 7. Let d˜1 = {{[0.2, 0.3], [0.3, 0.4], [0.2, 0.5]}, {[0.1, 0.2], [0.2, 0.5]}}, d˜2 = {{[0.2, 0.3], [0.5, 0.6]}, {[0.1, 0.2], [0.2, 0.3]}}, d̃3 = {{[0.1, 0.2]}, {[0.3, 0.4], [0.1, 0.3]}}, be three IVDHFEs. and w = (0.31, 0.38, 0.31)T be the standardized weight vector of d˜j (j = 1, 2, 3), Then, d(d1 , d2 ) = 0.3385, d(d1 , d3 ) = 0.5282, d(d2 , d3 ) = 0.7538. Therefore, sup(d1 , d2 ) = 0.6615, sup(d1 , d3 ) = 0.4718, sup(d2 , d3 ) = 0.2462. and T (d1 ) = 0.3976, T (d2 ) = 0.2814, T (d3 ) = 0.2398. w1 (1 + T (d1 )) n = 0.3321, j =1 wj (1 + T (dj )) w2 (1 + T (d2 )) n = 0.3733, j =1 wj (1 + T (dj )) w3 (1 + T (d3 )) n = 0.2946. j =1 wj (1 + T (dj )) When λ = 1, then GDHFPWA (d1 , d2 , d3 ) = {{[0.1718, 0.2719], [0.3050, 0.4092], [0.1718, 0.3082], [0.3050, 0.4387], [0.2077, 0.3489], [0.3352, 0.4716]}, {[0.1000, 0.2254], [0.1382, 0.2453], [0.1295, 0.2622], [0.1790, 0.2854], [0.1259, 0.3055], [0.1740, 0.3326], [0.1631, 0.3555], [0.2254, 0.3869]}}. and its score equals 0.1506. GDHFPWG (d1 , d2 , d3 ) = {{[0.1631, 0.2662], [0.2296, 0.3448], [0.1631, 0.2929], [0.2296, 0.3794], [0.1866, 0.3154], [0.2627, 0.4086]}, {[0.1000, 0.2309], [0.1642, 0.2650], [0.1387, 0.2683], [0.2002, 0.3007], [0.1345, 0.3420], [0.1963, 0.3712], [0.1718, 0.3740], [0.2309, 0.4018]}}. and its score equals 0.0540. International Journal of Intelligent Systems DOI 10.1002/int 804 YU, MERIGÓ, AND XU Figure 3. Comparison between GIVDHFPWA and GIVDHFPWG (λ ∈ (0, 10)). Taking λ ∈ (0, 10), the comparison between GIVDHFPWA operator and GIVDHFPWG operator is shown in Figure 3. 5. INFORMATION SYSTEMS SECURITY ASSESSMENT USING THE DHF GDM METHOD With the rapid development of information and computer technology, more and more people are on the information systems. At the same time, people have paid more and more attention to the security of information system. The safety of information system is very critical to an organization since any defects on privacy, integrity, and some other aspects may cause negative impacts. Information security assessment is the base and prerequisite of information system security, and it provides a fundamental basis for risk control and management. Owing to the complex nature of information security assessment, it often happened under uncertainty environment and responsible by a group of experts. Based on the existing research achievements,29,30 we adopt the following four criteria to evaluate the security of information systems including (1) organization securityc1 , (2) management securityc2 , (3) technical security c3 , and (4) personnel management security c4 . Generally speaking, the four criteria have different importance to the security of information systems; however, the study on weight information of the different criteria is beyond the scope of this study. Therefore, we suppose International Journal of Intelligent Systems DOI 10.1002/int GROUP DECISION MAKING IN INFORMATION SYSTEMS SECURITY 805 Table I. Review table for expert e1 . No. 1 2 3 4 Criteria Weight Organization security (c1 ) Management security (c2 ) Technical security (c3 ) Personnel management security (c4 ) 0.15 0.25 0.40 0.20 Description Evaluation results The satisfaction degree of four information systems regarding organization security The dissatisfaction degree of four information systems regarding organization security The satisfaction degree of four information systems regarding management security The dissatisfaction degree of four information systems regarding management security The satisfaction degree of four information systems regarding technical security The dissatisfaction degree of four information systems regarding technical security The satisfaction degree of four information systems regarding personnel management security The dissatisfaction degree of four information systems regarding personnel management security a1 a2 0.7 0.3 a3 a4 0.3 0.3 a1 a2 0.1 0.1 a3 a4 0.6 0.3 a1 a2 0.2 0.1 a3 a4 0.3 0.3 a1 a2 0.5 0.6 a3 a4 0.5 0.5 a1 a2 0.6 0.5 a3 a4 0.5 0.3 a1 a2 0.4 0.3 a3 a4 0.1 0.5 a1 a2 0.3 0.1 a3 a4 0.3 0.1 a1 a2 0.4 0.6 a3 a4 0.4 0.4 the weight vector of the four criteria is (0.15, 0.25, 0.40, 0.20)T . Suppose there are four information systems (x1 , x2 , x3 , x4 ) need to be assessed and this assessment is taken by a group of three experts (e1 , e2 , e3 ). To obtain the information given by the expert, the Tables I–III are designed and assigned to the three experts correspondingly. The experts are requested to select one number from the set = {0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0} to fill the table. The goal of this research is to evaluate the performance of the four information systems regarding their security. To do this, the following steps are adopted. Step 1. Collect information from experts and transform it to DHF information: Tables I–III are received from the three experts, based on which, the DHF decision-making matrix can be obtained and is shown in Table IV. Take the assessment information of the first information system a1 regarding organization security, for example, three experts all regard the satisfaction degree is 0.7. However, expert e1 think the dissatisfaction degree is 0.1, expert e2 believe the dissatisfaction degree is 0.3 and the expert e3 think the dissatisfaction degree is 0.2. In this situation, the comprehensive assessment information can be expressed by a DHFE {{0.7}, {0.1, 0.2, 0.3}}. Likewise, all the evaluation results from the three experts can be converted to DHF information and is shown in Table IV. International Journal of Intelligent Systems DOI 10.1002/int 806 YU, MERIGÓ, AND XU Table II. Review table for expert e2 . No. 1 2 3 4 Criteria Weight Organization security (c1 ) 0.15 Management security (c2 ) 0.25 Technical security (c3 ) Personnel management security (c4 ) 0.40 0.20 Description Evaluation results The satisfaction degree of four information systems regarding organization security The dissatisfaction degree of four information systems regarding organization security The satisfaction degree of four information systems regarding management security The dissatisfaction degree of four information systems regarding management security The satisfaction degree of four information systems regarding technical security The dissatisfaction degree of four information systems regarding technical security The satisfaction degree of four information systems regarding personnel management security The dissatisfaction degree of four information systems regarding personnel management security a1 a2 0.7 0.5 a3 a4 0.2 0.4 a1 a2 0.3 0.1 a3 a4 0.4 0.2 a1 a2 0.2 0.1 a3 a4 0.3 0.3 a1 0.5 0.7 a3 a4 0.5 0.6 a1 a2 0.6 0.5 a3 a4 0.6 0.4 a1 a2 0.4 0.3 a3 a4 0.2 0.6 a1 a2 0.2 0.1 a3 a4 0.4 0.1 a1 a2 0.6 0.7 a3 a4 0.3 0.5 Step 2. Calculate the T (DHFEij ) based on the DHF decision matrix: ⎡ 0.3772 ⎢0.2398 T (dij ) = ⎣ 0.4868 0.5067 0.4109 0.3224 0.4778 0.5667 0.3293 0.2223 0.3129 0.4496 ⎤ 0.4096 0.3724⎥ 0.5790⎦ 0.5101 Take the first information system, for example, the T (DHFE11 ), T (DHFE12 ), T (DHFE13 ), and T (DHFE14 ) were calculated as follows. The rest can be calculated in the same way. Since DHFE1 = {{0.7}, {0.1, 0.2, 0.3}}, DHFE2 = {{0.2, 0.3}, {0.5}}, DHFE3 = {{0.6}, {0.4}}, DHFE4 = {{0.1, 0.2, 0.3}, {0.4, 0.6}}. Then, the distance measures can be obtained based on Definition 7. d12 = 0.7637, d13 = 0.3160, d14 = 0.7774, d23 = 0.4536, d24 = 0.2158, d34 = 0.5497. International Journal of Intelligent Systems DOI 10.1002/int GROUP DECISION MAKING IN INFORMATION SYSTEMS SECURITY 807 Table III. Review table for Expert e3 . No. 1 2 3 4 Criteria Weight Organization security (c1 ) Management security (c2 ) Technical security (c3 ) Personnel management security (c4 ) 0.15 0.25 0.40 0.20 Description Evaluation results The satisfaction degree of four information systems regarding organization security The dissatisfaction degree of four information systems regarding organization security The satisfaction degree of four information systems regarding management security The dissatisfaction degree of four information systems regarding management security The satisfaction degree of four information systems regarding technical security The dissatisfaction degree of four information systems regarding technical security The satisfaction degree of four information systems regarding personnel management security The dissatisfaction degree of four information systems regarding personnel management security a1 a2 0.7 0.7 a3 a4 0.1 0.4 a1 a2 0.2 0.1 a3 a4 0.6 0.3 a1 a2 0.3 0.1 a3 a4 0.4 0.3 a1 a2 0.5 0.6 a3 a4 0.5 0.7 a1 a2 0.6 0.5 a3 a4 0.6 0.3 a1 a2 0.4 0.4 a3 a4 0.3 0.6 a1 a2 0.1 0.1 a3 a4 0.4 0.1 a1 a2 0.4 0.7 a3 a4 0.4 0.7 Table IV. DHF decision matrix. a1 a2 a3 a4 c1 c2 c3 c4 {0.7, 0.1,0.2, 0.3} {0.3,0.5,0.7, 0.1} {0.1,0.2,0.3, 0.4,0.6} {0.3,0.4, 0.2,0.3} {0.2,0.3, 0.5} {0.1, 0.6,0.7} {0.3,0.4, 0.5} {0.3, 0.5,0.6,0.7} {0.6, 0.4} {0.5, 0.3,0.4} {0.5,0.6, 0.1,0.2,0.3} {0.3,0.4, 0.5,0.6} {0.1,0.2,0.3, 0.4,0.6} {0.1, 0.6,0.7} {0.3,0.4, 0.3,0.4} {0.1, 0.4,0.5, 0.7} According to Equation (11) and weight vector of the four criteria (0.15, 0.25, 0.40, 0.20)T , we have, T (DHFE11 ) = w2 × sup(DHFE1 , DHFE2 ) + w3 × sup(DHFE1 , DHFE3 ) + w4 × sup(DHFE1 , DHFE4 ) = 0.3772 T (DHFE12 ) = w1 × sup(DHFE2 , DHFE1 ) + w3 × sup(DHFE2 , DHFE3 ) + w4 × sup(DHFE2 , DHFE4 ) = 0.4109 T (DHFE13 ) = w1 × sup(DHFE3 , DHFE1 ) + w2 × sup(DHFE3 , DHFE2 ) + w4 × sup(DHFE3 , DHFE4 ) = 0.3293 T (DHFE14 ) = w1 × sup(DHFE4 , DHFE1 ) + w2 × sup(DHFE4 , DHFE2 ) + w3 × sup(DHFE4 , DHFE3 ) = 0.4096 International Journal of Intelligent Systems DOI 10.1002/int 808 YU, MERIGÓ, AND XU Table V. Score values obtained by the GDHFPWA operator and the rankings of alternatives. Scores λ 0.1 1 5 10 a1 a2 a3 a4 –0.2913 0.0018 0.1970 0.2867 –0.5127 –0.1414 0.1415 0.2559 –0.2761 –0.0220 0.1581 0.2338 –0.4005 –0.2322 –0.1033 –0.0227 Ranking a1 a1 a1 a1 a3 a3 a3 a2 a4 a2 a2 a3 a2 a4 a4 a4 Table VI. Score values obtained by the GDHFPWG operator and the rankings of alternatives. Scores λ 0.1 1 5 10 a1 a2 a3 a4 Ranking 0.4886 0.2060 –0.0053 –0.0998 0.4367 0.0609 –0.2335 –0.3586 0.3905 0.1327 –0.0747 –0.1697 0.0729 –0.0976 –0.1984 –0.2367 a1 a2 a3 a4 a1 a3 a2 a4 a1 a3 a4 a2 a1 a3 a4 a2 Step 3. Using the GDHFPWA operator to aggregate the performance of four criteria for each information systems and ranking them: When we set the different values to parameter in the GDHFPWA operator, different values for comprehensive performance can be obtained for each information systems. We just express the scores and omit the DHFEs due to a large number of data. Score values obtained by the GDHFPWA and GDHFPWG operators and corresponding ranking results are shown in Table V and VI respectively. Figure 4 shows the scores of the four information systems obtained by the GDHFPWA operator as the parameter λ is set to different values; we can find that the scores for four information systems increase as the value of the parameter λ increases from 1 to 10. Furthermore, we find that (1) when λ ∈ [1, 6.777], the ranking of the four information systems is a1 a3 a2 a4 . (2) when λ ∈ [6.777, 10], the ranking of the four information systems is a1 a2 a3 a4 . Figure 5 shows the scores of the four information systems obtained by the GDHFPWG operator as the parameter λ is set to different values; we can find that the scores for four information systems decrease as the value of the parameter λ increases from 1 to 10. From Figure 5, we find that (1) when λ ∈ [1, 3.854], the ranking of the four information systems is a1 a3 a2 a4 . (2) when λ ∈ [3.854, 10], the ranking of the four information systems is a1 a3 a4 a2 . From the above research, we find that the safest information system is the a1 . International Journal of Intelligent Systems DOI 10.1002/int GROUP DECISION MAKING IN INFORMATION SYSTEMS SECURITY Figure 4. Scores for alternatives obtained by the GDHFPWA operator (λ ∈ (0, 10]). Figure 5. Scores for alternatives obtained by the GDHFPWG operator (λ ∈ (0, 10]). International Journal of Intelligent Systems DOI 10.1002/int 809 810 YU, MERIGÓ, AND XU 6. CONCLUDING REMARKS In this paper, we have extended the PA and PG operators to DHF environment and interval-valued DHF environment. Some aggregation operators have been proposed, such as DHFPWA, DHFPWG, GDHFPWA, and GDHFPWG operators. An application of the proposed operators to GDM was given, and a real example about the assessment of security for information systems is provided to illustrate our proposed methods. 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