J. Software Engineering & Applications, 2010, 3, 820-826
doi:10.4236/jsea.2010.38095 Published Online August 2010 (http://www.SciRP.org/journal/jsea)
Identifying and Modeling Non-Functional
Concerns Relationships
Hakim Bendjenna1, Pierre-Jean Charrel1, Nacer Eddine Zarour2
1University of Toulouse and Institut de Recherche en Informatique de Toulouse, Toulouse, France; 2Lire Laboratory, University
Mentouri of Constantine, Constantine, Algeria.
Received June 8th 2010; revised July 6th 2010; accepted July 10th 2010.
ABSTRACT
Requirements elicitation step is of paramount importance in the requirements engineering process. In the distributed
environment of so-called inter-company cooperative information system, this step is a thorny issue. To elicit require-
ments for an inter-company cooperative information system, we early proposed a methodology called MAMIE (from
MAcro to MIcro level requirements Elicitation) with an accompanied tool. In MAMIE methodology, requirements are
the result of composing functional and non-functional concerns. Before non-functional concerns composition, it’s pri-
mary to identify relationships between them. According to the most existing approaches, a non-functional concern may
have a negative, positive or null contribution on the other non-functional concerns. In this paper, we argue that using
only these three contributions types is not sufficient to express relationships which may exist between non-functional
concerns. Thus, we propose a process which aims to identify non-functional concerns’ relationships and model them
using a fuzzy cognitive map. The resulting model is composed of non-functional concerns, relationships between them
and the weight of these relationships expressed with linguistics fuzzy values. Using fuzzy cognitive maps to model
non-functional concerns relationships allows moving from the conventional modelling toward developing a computer
based model. An example from the textile industry is used to illustrate the applicability of our process.
Keywords: Non-Functional Concerns, Non-Functional Requirements, Soft-Goals, Non-Functional Concerns
Relationships, Fuzzy Cognitive Maps, Delphi Method
1. Introduction
Eliciting requirements for an Inter-company Cooperative
Information System (ICIS) is challenged by different
factors; most of which are related to communication be-
tween stakeholders [1]. The geographic and temporal
distance between stakeholders increases the difficulty to
elicit requirements [2]. In our previous research [3-5] we
proposed a methodology named MAMIE (from MAcro
to MIcro level requirements Elicitation) to elicit re-
quirements for an ICIS. One of the main contributions of
MAMIE methodology is coupling together goals, sce-
narios and viewpoints. Thus, requirements which do
emerge from MAMIE methodology exhibit a high degree
of completeness and consistency and, crucially, will em-
body the principal companies’ goals. In MAMIE, goals,
scenarios and viewpoints interact in a logical comple-
mentary way, where each concept plays a specific role:
goals describe the macro-level of requirements; scenarios
are used to describe the medium-level of requirements;
whereas viewpoints describe the micro-level of require
ments. A goal may be: a Functional Concern (FC) or a
Non-Functional Concern (NFC). We use here the term of
concern instead of requirement in order to refer to a high
level of abstraction. A FC represents a primary business
goal (e.g. build a car) while a NFC (e.g. security, per-
formance, compatibility) is a global property and usually
refers to a quality of FCs. Requirements are issued from
the composition of FCs and NFCs. Effectively, a sys-
tem’s utility is determined by both its functionality and
its non-functionality characteristics [6], known as NFCs,
non-functional requirements, or also soft-goals. None-
theless, there has been a lop-sided emphasis in the func-
tionality of the system, even though the functionality is
not useful or usable without the necessary non-functional
characteristics [6].
Before composing NFCs, the analyst must identify and
specify relationships between them. The most existing
approaches differentiate three types of relationships:
negative (-), positive (+) or null (no contribution) [7-9].
The opportunity to compose NFCs depends on the type

Identifying and Modeling Non-Functional Concerns Relationships 821
of these relationships. For example, when two NFCs
which contribute negatively to each other are composed,
then one NFC will influence negatively the correct
working of the other. Based on relationships types among
NFCs, the analyst may decide if the composition is or
not.
The interactions between NFCs need to prioritize
NFCs and then to define the degree of contribution of a
NFC to another NFC: two or more NFCs may not con-
tribute with the same degree to a specific NFC. For ex-
ample, Functionality and Aesthetics are two NFCs that
contribute positively to the NFC Service quality. How-
ever, Functionality ensures Service quality more accu-
rately than Aesthetics. Thus, defining explicit knowledge
about NFCs interactions may help to improve the com-
position process and then the requirements elicitation
process. This paper uses fuzzy cognitive maps [10,11] to
model interactions between NFCs. This formalism is
known to be used in ill-structured problems solving. It
allows observing the significance of each factor and its
influence on other factors and the final decision [12]. In
our context, a fuzzy cognitive map is composed of (1)
NFCs, (2) the type of relationships between them, and (3)
the weights of these relationships which indicate their
importance.
The rest of this paper is structured as follows. In Sec-
tion 2 we discuss related works. In Section 3 we give the
main features of fuzzy cognitive maps. In Section 4 we
present the three steps of a process to build a FCM which
identify and model NFCs and their relationships using a
fuzzy cognitive map. Section 5 shows the application of
this process to a case study. Finally, concluding remarks
are provided as well as future research issues.
2. Related Works
Most of the early work on NFCs focused on measuring
how much a software system is in accordance with the
set of NFCs that it should satisfy, using some form of
quantitative analysis [13-16], offering predefined metrics
to assess the degree to which a given software object
meets a particular NFC.
Recently, a number of works proposed to use ap-
proaches which explicitly deal with NFCs before metrics
are applicable [11,17-19]. These works propose the use
of techniques to justify design decisions on the inclusion
or exclusion of requirements which will impact on the
software design. Unlike the metrics approaches, these
latter approaches are concerned about making NFCs a
relevant and important part of the software development
process.
Boehm and In (1996) propose a knowledge base where
NFCs are prioritized through stakeholders’ perspectives,
dealing with NFCs at a high level of abstraction. Kirner
(1996) describe properties for six NFCs from the
real-time system domain: performance, reliability, safety,
security, maintainability and usability. This work pro-
vides heuristics on how to apply the identified properties
to meet the NFCs and later measure these NFCs.
A significant advance was introduced when NFCs
where treated as competing goals that are extensively
refined and traded off among each other in an attempt to
arrive at acceptable solutions. The non-functional re-
quirements Framework is one of the few works to deal
with non-functional requirements starting from the early
stages of software development through a broader per-
spective. The non-functional requirements Framework [6]
views non-functional requirements as goals that might
conflict among each other and must be represented as
soft-goals to be satisficed. The soft-goal concept was
introduced to cope with the abstract and informal nature
of non-functional requirements. 4 types of contribution
have been proposed to describe relationships among
non-functional requirements: make (++), help (+), hurt
(-), break (--). However, as important as getting a
well-formed and as-complete-as-possible set of contribu-
tion types, we need to understand how to identify and
model these relationships. None of the above work tack-
les this problem.
3. Fuzzy Cognitive Maps: A Brief
Description
In this section, we describe some features of fuzzy cogni-
tive maps. Cognitive Maps (CMs) were proposed by R.
Axelrod (1976) in order to solve ill-structured problems.
A CM is a signed digraph designed to capture the causal
assertions of a person with respect to a certain domain
and then uses them in order to analyze the effects of al-
ternative, e.g. policies, business decisions, etc. upon cer-
tain goals. A cognitive map is based on two notions:
 The concept which is represented by a variable.
 The causal belief which defines a relationship
among variables. These relationships link variables to
each other and they can be either positive or negative.
Variables that cause a change are called cause vari-
ables while those that undergo the effect of the change in
the cause variable are called effect variables. If the rela-
tionship is positive, an increase or decrease in a cause
variable causes the effect variable(s) to change in the
same direction. If the relationship is negative, then the
change which the effect variable undergoes is in the op-
posite direction. Figure 1 is a graphical representation of
a cognitive map, where variables (X, Y, Z, F, W) are
represented as nodes, and causal relationships as directed
arrows between variables, thus constructing a signed
digraph.
Another way of representing a cognitive map is possi-
ble through an adjacency matrix where one can clearly
observe the sign of the relationship, while keeping in
mind that in case of there being an absence of relation-
ship between these two factors, the corresponding entry

Identifying and Modeling Non-Functional Concerns Relationships 822
X
Y F
W
Z
+
--
+
+
Figure 1. An example of Cognitive Map [10]
will be empty [10]. Figure 2 shows this matrix (E) that
represents an example of a CM.
CMs were developed in simulation, organizational
strategies modelling, support for strategic problem for-
mulation and decision analysis, knowledge bases con-
struction, managerial problems diagnosis, failure modes
effects analysis, modelling of social and psychological
processes, modelling virtual worlds and analysis of their
behaviour, requirements analysis and systems require-
ments specification [12,20,21].
B. Kosko (1986) introduces Fuzzy Cognitive Maps
(FCMs) i.e. weighted cognitive maps with fuzzy weights.
It is argued that FCM eliminate the indeterminacy prob-
lem of the total effect. Since its development, fuzzy set
theory has been advanced and applied in many areas such
as experts systems and decision making, control engi-
neering, pattern recognition, etc. [21]. It is argued that
people use fuzzy data, vague rules, etc. and fuzzy sets as
a mathematical way to represent vagueness [22].
+
+
-
Figure 2. Adjacency matrix associated with a cognitive map
[10]
Different approaches were proposed for the specifica-
tion of the fuzzy weights in a FCM [23]. One suggestion
is to ask the experts to assign a real number from the
interval (0, 1) for each relationship and then calculate the
average of these numbers. However, it is difficult for the
experts to assign a real number in order to express their
beliefs with regard to the strength of relationships. This
is the reason why partially ordered linguistic variables
such as weak < moderate < strong, etc. are preferred in-
stead of real number.
4. A Process to Model NFCs Interaction
Using Fuzzy Cognitive Maps
To model interactions between NFCs using a FCM, we
present in this section a process composed of three steps:
1) Identify NFCs, 2) Identify relationships between
NFCs, 3) Specify the fuzzy weights and so provide the
FCM. A simple view of this process is depicted in Figure
3.
4.1 Step 1: Identify NFCs
The first step consists on identifying all the NFCs of a
system. NFCs are global properties (assumptions, con-
straints, etc.) that can influence part or the whole system
[6]. NFCs can be identified using several approaches
such as those used to identify goals. Here we have taken
the main ideas from Chung (2000) who proposed a cata-
logue of NFCs.
The analyst with the other stakeholders identifies
which subset of these NFCs is applicable to the system.
For each entry in the catalogue, we must decide whether
it would be useful in our system or not.
For example, if the owner of a vehicle has to indicate,
during registration, his/her bank account details, so that
automatic transfers can be performed automatically, then
Step 3
Step 2
Step 1
First round
Identify
NFCs
Design the
initial CM
Second round
Final CM
Initial CM
Specify the
fuzzy weightsFinal FCM
Delphi
hd
A set of
Figure 3. Steps needed to model NFCs interactions using a FCM
E =
W
X
Y
Z
W X Y Z

Identifying and Modeling Non-Functional Concerns Relationships 823
Security is an issue that the system needs to address.
Other NFCs may be identified in this example from ca-
talogue are Legal Issues and Correctness. Certain NFCs
appear time and again during system development and
most of them are likely to be domain-specific [6].
4.2 Step 2: Identify Relationships between NFCs
The objective of this step is to understand and define the
relations between the identified NFCs. When the NFCs
and their relations are clearly recognized, it is possible to
establish the final CM.
In order to determine relations between NFCs, the
analyst asks advices to a panel of experts. The analyst
chooses experts according to their experience and back-
ground in the field. The number of experts may depend
on the characteristics of the field. One of the most recent
studies suggests a range of 10 to 18 to be an ideal num-
ber for each panel of experts [24]
The analyst starts by designing an initial/draft CM, ei-
ther alone or with help of an expert. In order to reach
consensus between experts, several techniques have been
proposed [25]. Here, due to its simplicity we adopt Del-
phi methodology. Delphi is used to structure the commu-
nication process within a group of experts in order to
reach a consensus regarding a complex problem [26].
Delphi method is organised in two consulting rounds.
After the first round the experts receive feedback reports.
They have the opportunity of improving their own opin-
ion based on this feedback.
At the beginning of the second round experts are pro-
vided with information about deviations from the first
round. Often a larger consensus than the first round can
be observed. The goal is to obtain consensus and get all
experts to go toward the average [26].
To apply Delphi in our context, we define the follow-
ing steps:
1) The first round.
 The analyst gives the initial CM to all chosen ex-
perts.
 The analyst asks them to check and comments the
initial CM.
 Experts may change the type of relationships be-
tween NFCs in the initial CM (e.g. from negative contri-
bution to positive contribution), they may also delete
existing relationships; add new relationships or new
NFCs.
 The analyst revises the draft CM on the basis of the
answers of experts and builds a new CM. For each rela-
tionship in the new CM, the analyst determines the num-
ber of experts who issues the same evaluation (positive,
negative or null). These results are collected in a table.
2) The second round.
 The new CM with the table resulting from the first
round are sent to experts for revision. Instructions for
giving advices are the same as in the first round.
 The analyst collects the results of the second round.
A consensus is reached either because the experts are
influenced by the others in the second round, or because
they have realized that their previous opinion was erro-
neous.
 The analyst builds the final version of the CM,
based on the answers of the experts.
The purpose of the next step is to extend this CM to a
FCM.
4.3 Step 3: Specify the Fuzzy Weights and so
Provide the FCM
Up to the previous step, the cognitive map has been pro-
duced. In this cognitive map, no certain strengths for
causal relations between NFCs are considered. The objec-
tive of this step is to provide such strength for the relations
using the fuzzy set theory. To do so, each mutual relation-
ship includes one linguistic fuzzy weight which deter-
mines the accuracy of the expert choice. Following W. R.
Zhang (1989) (1992) [27,28] we use the linguistic fuzzy
weights instead of real values for weights, since they
make it easier for the planners to express their beliefs.
These linguistic fuzzy weights bring about a more
thorough and understandable vision for the decision
makers by mapping the ideas of the experts into a logic
which could be processed [29].
In order to identify the linguistic fuzzy weights the
analyst identifies the response to the following question
for each relationship in the CM:
How strong, the causal relationship between NFCs in
the final CM is?
The response to this question is an element from the
following set: {Weak, Moderate, Strong, and Undefined},
where Weak < Moderate < Strong.
In order to express their beliefs in the strength of a
certain causal relationship as being strong, moderate, or
weak, the experts assign fuzzy weights to all of the rela-
tionships in the cognitive map. The corresponding fuzzy
weights range is between 0 and 1. The goal of this step is
not to reach a consensus between experts, thus the ana-
lyst is not limited by any number of experts. To give
weights to the CM, the analyst chooses a number of ex-
perts from the panel of experts who agree with the CM
obtained in the previous step.
The evaluations of the weight of a specific relationship
may be different over experts. In order to aggregate all
these evaluations, we propose to compute the average of
these weights. The result may classify the strength of
relationships as weak, moderate or strong.
5. A Case Study
A group of specialized companies in a regional environ-
ment wish to cooperate together in order to produce a
range of textile products. These groups of 5 participating

Identifying and Modeling Non-Functional Concerns Relationships 824
companies with their locations are the following:
 The fiber producer company (Morocco).
 The knitting mills and weaver company (France).
 The dyer and finisher company (France).
 The designer company (Spain).
 And the manufacturer company (Italy).
The analyst who is in France applies MAMIE method-
ology to elicit requirements for the future system. In this
paper, we present the result of applying the process pre-
sented to identify and model relationships between
NFCs.
5.1 Step 1: Identify NFCs
The analyst with the other stakeholders has identified the
following set of NFCs: Product quality (NFC1), Func-
tionality (NFC2), Product cost (NFC3) and Competitive-
ness (NFC4).
5.2 Step 2: Identify Relationships between NFCs
The result of this step is a final CM. To obtain it, the
analyst chooses 10 experts. S/he starts by building an
initial CM with one expert. Figure 4 depicts the result of
this sub-step.
In order to obtain the final CM, the analyst applies
Delphi method. Table 1 summarises the advices of the
experts on the initial CM: for each relationship between
NFCs, the table collects the number of experts who agree
with its type (positive, negative or null).
We may remark that:
 The experts reach a consensus for almost all the re-
lationships, i.e. in most cases they have responded in the
same way.
 Product aesthetics (NFC5) is a new NFC added by 6
experts. They estimate that it has a positive relation with
Product quality NFC (NFC1)
According to the consequences of the first round of Del-
Functionality
(NFC
2
)
Product Quality
(
NFC
1
)
Product Cost
(NFC
3
)
- +
Competitiveness
(NFC
4
)
+
Figure 4. The initial CM
Table 1. First round: distribution of the experts’ responses
Relation-
ships
Positive
relationship
Negative
Relationship
No
relationship
NFC2-NFC1 10 0 0
NFC1-NFC4 9 1 0
NFC3-NFC4 3 6 1
NFC5-NFC1 6 0 4
phi methodology, the initial cognitive map needs some
improvements and corrections.
After applying these revisions, the second round starts
up. The revised cognitive map with the frequency of re-
sponses obtained at the end of the first round is sent to
the experts. The analyst asks them to explore the rela-
tions in the new cognitive map and insert their opinions.
The results of the second round are collected in Table 2.
We observe that the experts have made some compro-
mises. Figure 5 depicts the final CM.
5.3 Specify the Fuzzy Weights and so Provide the
FCM
In order to determine the weights of the relations identi-
fied in the previous step, the analyst asks the following
question to the experts:
How strong, do you believe, the causal relationship
between NFCs in the final CM is?
The experts express their beliefs in the strength of a
certain causal relationship, by assigning a fuzzy weight
ranging between 0 and 1 where, we consider that:
 0 < Low < 0.25;
 0.25 <= Moderate < 0.75;
 0.75 <= Strong <= 1.
Table 3 summarizes the results where Ei denotes the
Table 2. Second round: distribution of the experts’ re-
sponses
Relationships Positive
relationship
Negative
relationship
No
relationship
NFC2-NFC1 10 0 0
NFC1-NFC4 9 1 0
NFC3-NFC4 1 8 1
NFC5-NFC1 10 0 0
Figure 5. The final CM
Table 3. Experts’ evaluations for relationships fuzzy wei-
ghts
RelationshipsE1 E2 E3 E4 E5 E6 E7
NFC2-NFC10.80 0.850.90 1,00 0.80 0.950.90
NFC1-NFC40.85 0.900.80 0.90 1,00 0.920.87
NFC3-NFC40.30 0.280.40 0.45 0.50 0.400.35
NFC5-NFC10.40 0.350.45 0.50 0.48 0.550.60
+
Product aesthetics
(NFC5)
+
+
-
Competitiveness
(NFC4)
Product Cost
(NFC3)
Product Quality
(NFC1)
Functionality
(
NFC2
)

Identifying and Modeling Non-Functional Concerns Relationships 825
i-th expert and i=1,..,7, i.e. 7 experts participate to this
step.
The weight of each relationship is the average of the
experts’ evaluation for this relationship. The value re-
turned by this function allows attributing a linguistic
fuzzy weight. Table 4 shows the results.
The final FCM is the labelled CM with its fuzzy lin-
guistic weights depicted by Figure 6.
Figure 7 depicts a screen-dump of MAMIE-Tool
when NFCs are identified and specified with their rela-
tionships.
The managers and planners can use this FCM to in-
crease the competitiveness and to improve the product
quality by analyzing different choices; such as decreasing
the product cost. Thus, using a FCM to model relation-
ships between NFCs provides a way to identify how to
reach goals
Table 4. Linguistics weights of relationships between NFCs
Relationships Average value
Weights of rela-
tionships
NFC2-NFC1 0.88 Strong
NFC1-NFC4 0.89 Strong
NFC3-NFC4 0.38 Moderate
NFC5-NFC1 0.47 Moderate
Product Cost
(
NFC
3
)
+ moderate
Product aesthetics
(NFC
5
)
+strong
+ strong
- moderate
Competitiveness
(NFC
4
) Functionality
(NFC
2
)
Product
Quality (NFC
1
)
Figure 6. The final FCM
Figure 7. MAMIE-Tool interface-NFCs’ relationships
6. Conclusion and Future Works
This paper presents a process to identify and model rela-
tionships between non-functional concerns. To do so, we
chose fuzzy cognitive maps which have been introduced
to model ill-structured complex systems. Building a
fuzzy cognitive map follows an approach similar to hu-
man reasoning and the human decision-making process.
They can successfully represent knowledge and human
experience; introduce concepts to represent the essential
elements and the cause and effect relationships among
the concepts to model the behaviour of any system. It is a
very convenient, simple, and powerful tool, which is
used in numerous fields.
The process presented in this paper starts by identify-
ing non-functional concerns. Then, the analyst builds an
initial cognitive map for the identified non-functional
concerns. In order to obtain consensus for a final cogni-
tive map between experts, Delphi method is used. A
fuzzy linguistic value for a specific relationship is ob-
tained by calculates the average of all the evaluations
values given by experts. Then s/he classifies it as weak,
moderate or strong. Using fuzzy linguistics labels makes
the fuzzy cognitive map more sensible. In addition, the
presented process enables the experts to simulate idea
from various viewpoints.
We believe that using a fuzzy cognitive map to model
non-functional concerns relationships proves useful and
looks promising for a move from the conventional mod-
elling toward developing computer based model.
Thus, further works will concentrate on two objec-
tives:
 Design an expert system based on fuzzy cognitive
maps.
 Study the use of the presented process in the context
of Aspect Oriented Requirements Engineering (AORE)
area to handle interactions between aspects. AORE aims
at addressing crosscutting concerns by means of aspects
to provide their identification, separation, representation
and composition.
7. Acknowledgements
This research is partially supported by the PHC TASSILI
project under the number 10MDU817. We thank the
anonymous reviewers for providing valuable comments.
REFERENCES
[1] F. P. Brooks, “No Silver Bullet: Essence and Accidents of
Software Engineering,” IEEE Computer Journal, Vol. 20,
No. 1, 1987, pp. 10-19.
[2] B. H. C. Cheng and J. M. Atlee, “Research Directions in
Requirements Engineering,” Proceedings of the Future of
Software Engineering Conference, Minneapolis, IEEE
Computer Society, 2007, pp. 285-303.
Relationship between Product cost and
Competitiveness NFCs

Identifying and Modeling Non-Functional Concerns Relationships 826
[3] H. Bendjenna, N. Zarour and P. J. Charrel, “MAMIE, A
Methodology to Elicit Requirements for an Inter-Com-
pany Cooperative Information System,” Proceeding of
IEEE Conference on Innovation on Software Engineering
(ISE), Vienna, IEEE Computer Society, 2008, pp. 290-
295.
[4] H. Bendjenna, N. Zarour and P. J. Charrel, “Enhancing
the Elicitation Technique Selection Process in a Coopera-
tive Distributed Environment,” Proceeding of the 14th
Requirements Engineering Foundation for Software
Quality Conference (REFSQ), Montpellier, Lecture Notes
in Computer Science, Vol. 5025, Springer, Heidelberg,
2008, pp. 23-36.
[5] H. Bendjenna, M. Amroune, N. Zarour and P. J. Charrel,
“Prioritizing Non-functional Concerns in MAMIE Meth-
odology,” Proceeding of the Third International Confer-
ence on Knowledge Science, Engineering and Manage-
ment (KSEM), Vienna, Lecture Notes in Artificial Intelli-
gence, Vol. 5914, Springer, Heidelberg, 2009, pp. 253-
262.
[6] L. Chung, B. Nixon, E. Yu and J. Mylopoulos, “Non-
Functional Requirements in Software Engineering,” Klu-
wer Academic Publishers, New York, 2000.
[7] P. J. A. Diaz, F. Trilnik and M. R. Campo, “How to Han-
dle Interaction Concerns?” Proceedings of the ACM Con-
ference on Object-Oriented Programming, Systems, Lan-
guages, and Applications OOPSLA’00, Minneapolis,
2000, pp. 32-52.
[8] J. Liu, D. Batory and S. Neduniry, “Modelling Interac-
tions in Feature Oriented Software Design,” International
Conference on Feature Interactions in Telecommunica-
tions and Software Systems (ICFI), Leicester, 2005, pp.
178-197.
[9] F. Sanen, E. Truyen, W. Joosen, N. Loughran, A. Rashid,
A. Jackson, A. Nedos and S. Clarke, “Study on Interac-
tion Issues,” AOSD-Europe Deliverable, Vol. 44, Leuven,
2006, pp. 1-31.
[10] R. Axelrod, “Structure of Decision: The Cognitive Maps
of Political Elites,” Princeton University Press, Princeton,
1976.
[11] H. J. Zimmermann, “Fuzzy Set Theory and its Applica-
tions,” Kluwer Academic Publishers, Dordrecht, 1991.
[12] S. Bueno and J. L. Salmeron, “Fuzzy Modeling Enter-
prise Resource Planning Tool Selection,” Computer Stan-
dards & Interfaces, Vol. 30, No. 3, 2008, pp. 137-147.
[13] B. Boehm, “Characteristics of Software Quality,” North
Holland Press, New York, 1978.
[14] N. E. Fenton and S. L. Pfleeger, “Software Metrics: A
Rigorous and Practical Approach,” 2nd Edition, Interna-
tional Thomson Computer Press, London, 1997.
[15] S. E. Keller, L. G. Khan and R. B. Panara, “Specifying
Software Quality Requirements with Metrics,” In: R. H.
Thayer and M. Dorfman, Eds., Tutorial: System and
Software Requirements Engineering, IEEE Computer So-
ciety Press, Piscataway, 1990, pp. 145-163.
[16] M. R. Lyu, “Handbook of Software Reliability Engineer-
ing,” McGraw-Hill, New York, 1996.
[17] B. Boehm and H. In, “Identifying Quality-Requirement
Conflicts,” IEEE Software Journal, Vol. 13, No. 2, 1996,
pp. 25-35.
[18] L. M. Cysneiros, J. C. S. P Leite and J. S. M. Neto, “A
Framework for Integrating Non-Functional Requirements
into Conceptual Models,” Requirements Engineering
Journal, Vol. 6, No. 2, 2001, pp. 97-115.
[19] T. G. Kirner and A. M. Davis, “Non-functional Require-
ments of Real-Time Systems,” Advances in Computers
Journal, Vol. 42, No. 1, 1996, pp. 1-37.
[20] D. Kardaras and B. Karakostas, “The Use of Fuzzy Cog-
nitive Maps to Simulate the Information Systems Strate-
gic Planning Process,” Information and Software Tech-
nology Journal, Vol. 41, No. 1, 1999, pp. 97-210.
[21] B. Kosko, “Fuzzy Cognitive Maps,” International Jour-
nal on Man-Machine Studies, Vol. 24, No. 1, 1986, pp.
65-75.
[22] J. Bezdek, “Fuzzy Models-What Are They, and Why,”
IEEE Transactions on Fuzzy Systems, Vol. 1, No. 1, 1993,
pp. 1-6.
[23] R. Taber, “Knowledge Processing with Fuzzy Cognitive
Maps,” Expert Systems with Applications Journal, Vol. 2,
No. 1, 1991, pp. 83-87.
[24] C. Okoli and S. Pawlowski, “The Delphi Method as a
Research Tool: An Example, Design Considerations and
Applications,” Information & Management, Vol. 42, No.
1, 2004, pp. 15-29.
[25] N. Bryson, A. Mobolurin and A. Joseph, “Generating
Consensus Fuzzy Cognitive Maps,” Intelligent Informa-
tion Systems, Vol. 8, No. 10, 1997, pp. 231-235.
[26] N. C. Dalkey and O. Helmer, “An Experimental Applica-
tion of the Delphi Method to the User of Experts,” Man-
agement Science Journal, Vol. 9, No. 3, 1963, pp. 458-
467.
[27] W. R. Zhang, S. S. Chen and J. C. Bezdek, “A Generic
System for Cognitive Map Development and Decision
Analysis,” IEEE Transactions on Systems, Man, and Cy-
bernetics, Vol. 19, No. 1, 1989, pp. 31-39.
[28] W. R. Zhang, S. S. Chen, W. Wang and R. King, “A Cog-
nitive-Map-Based Approach to The Coordination of Dis-
tributed Cooperative Agents,” IEEE Transactions on
Systems, Man, and Cybernetics, Vol. 22, No. 1, 1992, pp.
103-114.
[29] G. J. Klir and B. Youan, “Fuzzy Sets and Fuzzy Logic,
Theory and Applications,” Prentice Hall, India, 2005.