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Int. J. Computer Applications in Technology, Vol. X, No. Y, 200X 1
Copyright © 200X Inderscience Enterprises Ltd.
Decision support under uncertainties based on
robust Bayesian networks in reverse logistics
management
Eduard Shevtshenko*
Department of Machinery,
Tallinn University of Technology,
Ehitajate tee 5, 19086, Tallinn, Estonia
E-mail: eduard.shevtshenko@ttu.ee
*Corresponding author
Yan Wang
Department of Industrial Engineering & Management Systems,
University of Central Florida,
4000 Central Florida Blvd.,
Orlando, Florida 32816-2993, USA
E-mail: wangyan@mail.ucf.edu
Abstract: One of the major challenges for product lifecycle management systems is the lack of
integrated decision support tools to help decision-making with available information in
collaborative enterprise networks. Uncertainties are inherent in such networks due to lack of
perfect knowledge or conflicting information. In this paper, a robust decision support approach
based on imprecise probabilities is proposed. Robust Bayesian belief networks with interval
probabilities are used to estimate imprecise posterior probabilities in probabilistic inference. This
generic approach is demonstrated with decision-makings in design for closed-loop supply chain.
The ultimate goal of robust intelligent decision support systems is to enhance the effective use of
information available in collaborative engineering environments.
Keywords: product lifecycle management; PLM; reverse logistics; interval analysis; imprecise
probability; Bayesian network.
Reference to this paper should be made as follows: Shevtshenko, E. and Wang, Y. (xxxx)
‘Decision support under uncertainties based on robust Bayesian networks in reverse logistics
management’, Int. J. Computer Applications in Technology, Vol. X, No. Y, pp.000–000.
Biographical notes: Eduard Shevtshenko is working in Tallinn University of Technology as a
Researcher since 2003. He received his BS, MS and PhD from the Department of Mechanical
Engineering at the Tallinn University of Technology (TUT). He teaches international MS courses
at TUT and consults with international corporations. His principal research areas include
ERP/DSS/MRP, knowledge management and collaborative enterprise networks.
Yan Wang is an Assistant Professor at the Department of Industrial Engineering and
Management Systems, University of Central Florida. He received his BS from Tsinghua
University, MS from Chinese Academy of Sciences and PhD from the University of Pittsburgh.
His research interests include engineering design, modelling, simulation and visualisation.
1 Introduction
Under the pressure from global competition, corporations
have shown interests in the close cooperation with partners
in the past few years. Small and medium-sized companies
have particularly been determined to set up cooperation
networks. The competition in business has changed from
company versus company to business network versus
business network (Zheng and Possel, 2002).
Collaborative product development among designers,
manufacturers, suppliers, vendors, users and other
stakeholders is one of the keys for manufacturers to improve
product quality, reduce cost and shorten time-to-market in
global competition. Collaborative design is the new design
process where multidisciplinary stakeholders participate in
design decision-making and share product information
across enterprise boundaries in an internet-enabled
distributed environment. New technologies for collaborative
design were developed recently, such as agent system (Shen
et al., 2001), collaborative environment (Sriram, 2002),
information management (Huang and Mak, 2003) and
intelligent system (Zha, 2007).
2 E. Shevtshenko and Y. Wang
Product lifecycle management (PLM) systems have
been widely accepted as the major enterprise-level platform
for information sharing and integration in collaborative
design and manufacturing. It consists of a collection of
software tools including product data management (PDM),
enterprise resource planning (ERP), collaboration process
management (CPM), customer relationship management
(CRM), supplier relationship management (SRM),
document knowledge management (DKM), environment
health and safety management (EHSM) and others. Yet, one
of the major challenges for PLM systems is the lack of
integrated decision support tools to help decision-making
with available information within the systems.
This paper addresses the need of decision support in the
collaborative networks of production enterprises. An
intelligent decision support system (IDSS) should integrate
with different ERP systems in such networks of
collaborative enterprises. An IDSS is a strategic and tactical
tool capable of supporting a variety of users in making
informed decisions. Information from this system will be
used to support both the external and internal objectives of a
corporation. The role of the IDSS is to suggest solutions
given certain situations. Thus human users can assess the
proposals prepared by the system and make decisions. The
IDSS enables enterprise networks to be less dependent on
personal experiences of employees and facilitate enterprise
knowledge accumulation.
The effectiveness of an IDSS is dependent on the
alignment of two conditions: the ability to collect the
required data from the business functions and the
conversion of the data into useful information. One
challenge of decision-making in such collaborative
networks is uncertainty. Uncertainty is due to lack of perfect
knowledge or enough information. It is also known as
epistemic uncertainty and reducible uncertainty. There are
several sources of uncertainties in collaborative networks,
including:
• Lack of data: the basic function of ERP systems is to
collect and share information. When collaboration is
across enterprise boundaries, not all enterprise data are
sharable. Sensitive parameters, trading secrets and other
intellectual properties from other companies usually are
not available.
• Conflicting information: if there are multiple sources of
information through different ERP systems or
databases, decision-makers may face conflicts among
them. It is not wise to draw simple conclusions without
considering the contradictory evidence.
• Conflicting beliefs: when data are not available,
decision-makers usually depend on domain experts’
opinions. The judgments from those experts can be
different due to the diversity of their past experiences.
• Lack of introspection: decision-makers may not be able
to afford the necessary time to think deliberately about
an uncertain event. Lack of introspection makes
decision-making inherently risky.
• Measurement errors: the data collected by the ERP
systems may contain errors due to measuring
environments and human errors. The quality of
collected quantities affects decision-makers’ judgments.
Therefore, uncertainty should be incorporated in the IDSS
for enterprise networks. Traditionally, Bayesian networks
are used to accommodate uncertainties in probabilistic
inference. In a dynamic business environment,
decision-makers usually are required to make proper
decisions related to product portfolio, platform selection,
material flow and others based on the latest available
information. Bayesian networks are convenient in updating
prior knowledge based on the extra information. They
capture relationships among random variables and provide a
reasoning approach with the underlying Bayes’ theorem.
Bayesian networks have been widely applied in
classification, data fusion, information retrieval and decision
support. Nevertheless, the traditional Bayesian networks do
not differentiate uncertainty from variability. Variability is
due to the inherent randomness in a system. It is irreducible
even by additional measurements and extra information.
Therefore, variability is different from uncertainty. The
traditional Bayesian networks consider variability and
uncertainty collectively and simply represent them with
probability distributions.
Uncertainty in Bayesian networks are manifested as
impreciseness of probability distributions due to lack of
knowledge. For instance, the probability that our market
share will go up in the next six months is between 0.2 and
0.4, instead of 0.3 precisely or the probability that our new
product will last longer than ten years is between 0.7 and
0.8. The impreciseness directly affects the robustness of the
reasoning process. This impreciseness can be interpreted as
uncertain situations. In such cases, we intend to consider a
range of possible scenarios, instead of one, to ensure the
robustness during decision-making.
In this paper, we propose a new decision-making
approach based on robust Bayesian networks under
uncertainty for IDSS, where interval-valued imprecise
probabilities are used. Interval values consider a range of
situations and represent uncertainties. In combination with
probabilities that address variabilities, imprecise
probabilities with lower and upper bounds allow us to
consider a range of possible scenarios simultaneously in
probabilistic inference. Incorporating uncertainties in
stochastic models is particularly important when the size of
available data is small or contradictory evidence does not
allow us to reach consensus.
In the remainder of the paper, Section 2 gives a brief
overview of Bayesian network and imprecise probability. In
Section 3, we present the proposed robust Bayesian belief
networks (BBNs) for decision-making under uncertainties in
IDSS systems. In Section 4, we apply the new probabilistic
reasoning approach to a general framework of closed-loop
supply chain and illustrate it with an example of circuit
board lifecycle decision-making in Section 5.
Decision support under uncertainties based on robust Bayesian networks in reverse logistics management 3
2 Background
2.1 Bayesian belief network
A BBN is a probabilistic graphical model with elements of
nodes, arrows between nodes and probability assignments.
We can consider a Bayesian network as a directed acyclic
graph in which nodes represent random variables, where the
random variable may be either discrete or continuous. In the
case of discrete variables, they represent finite sets of
mutually exclusive states which themselves can be
categorical. Bayesian networks have a built-in
computational architecture for computing the effect of
evidence on the states of the variables.
BBN is able to update the probabilities of variable states
while learning new evidence. It also utilises probabilistic
independence relationships, both explicitly and implicitly
represented in graphical models, in order to compute
efficiently for large and complex problems (Taroni et al.,
2006).
In BBN, the decision-maker is concerned with
determining the probability that a hypothesis (H) is true,
from evidence (E) linking the hypothesis to other observed
states of the world. The approach makes use of the Bayes’
rule to combine various sources of evidence. The Bayes’
rule states that the posterior probability of hypothesis H
given that evidence E is present or P(H|E), is
PE HPH
PH E PE
=(| )()
(|) ()
where P(H) is the probability of the hypothesis being true
prior to obtaining the evidence E and P(E|H) is the
likelihood of obtaining the evidence E given that the
hypothesis H is true.
When the evidence consists of multiple sources denoted
as 12 n
EE E…,,,, each of which is conditionally
independent, the Bayes’ rule can be expanded into the
expression:
1
1
n
j
j
jn
j
j
j
PE HPH
PH E
PE
=
=
=
∏
∏
(|)()
(| )
()
∩
The BBN architecture updates probabilities of the variable
states on learning new evidence.
The BBN approach has been applied in solving
manufacturing and production related problems. For
instance, an interesting approach of online alert systems for
production plants was proposed (Nielsen and Jensen, 2007).
A methodology was developed for detecting fault and
abnormal behaviours in production plants. This
methodology has been successfully tested on both real
world data from a power plant and simulated data from an
oil production facility.
BBN was applied in root cause diagnostics of process
variations (Dev and Story, 2005). It is an effective tool to
explicitly address input uncertainty and utilise data from
multiple sources. After being trained with data sets, the
network was able to diagnose the correct state at a 60%
confidence level.
BBN was also successfully implemented for technology
planning (Spath and Agostini, 1997). The aim was to design
a system for adaptive planning with integrated feedbacks
from real time process data and experiences. A Bayesian
structure was derived from historical data stored as
processing elements. It was allowed to update the network
(both the structure and the probabilities) and to expand,
improve or optimise the decision base.
BBN has also been used as the knowledge base of
reasoning systems for supply chain diagnostics and
prediction, vendor appraisal, customer assessment,
evaluation of strategic or technical alliance (Kao et al.,
2005). The participating enterprises in the supply chain can
solve the reasoning problems based on the networks.
The different applications mentioned above are based on
the traditional BBN models, where probabilities are
assumed to be precisely known. When this assumption does
not necessarily hold, the robustness of BBN should be
aware of. Sensitivity analysis is the common approach to
study the effect of uncertainty by introducing the variations
of probability values.
A neighbourhood concept from sensitivity analysis,
called ε-contamination model, is usually used to study the
robustness (Insua and Ruggeri, 2000). It is focused on
replacing a single prior distribution by a class of priors.
Computing the range of the ensuring answers as the prior
varying over the class is based on the model.
{
}
0
1PP P QQΓ= = − + ∈:() ,
εεε ϑ
where
Γ
ε is the ε-neighbourhood of probability 0
P and ϑ
is called the class of contaminations that contains some
arbitrary probability measurement .Q The popularity of the
model arises, in part, from the ease of its specification and
from the fact that it can be easily handled by the traditional
precise probability theory.
In this paper, we propose a different approach to
incorporate uncertainty in probabilistic inference. We
integrate interval-based imprecise probabilities into
Bayesian networks in order to improve the robustness of
reasoning. The foundation of our approach is imprecise
probability, as introduced in Section 2.2.
2.2 Imprecise probability
Imprecise probability is a generalisation of traditional
probability to differentiate uncertainty from variability both
qualitatively and quantitatively. An interval-valued
probability pp[, ]
with the lower and upper bounds captures
imprecision and indeterminacy. The width of the interval
reflects the degree of uncertainty.
There have been several representations of imprecise
probabilities. For example, behavioural imprecise
probability theory (Walley, 1991a) models behavioural
4 E. Shevtshenko and Y. Wang
uncertainties with the lower prevision PX() (a maximal
acceptable buying price for the uncertain reward X) and the
upper prevision PX P X=− −() ( ) (a minimal acceptable
selling price for X). Coherence principles are developed to
avoid sure loss and natural extension. The Dempster-Shafer
evidence theory (Dempster, 1967; Shafer, 1976)
characterises uncertainties by the aid of basic probability
assignments m(A) associated with the focal element A. A
belief-plausibility pair, Bel( ) ( )
ii
BA
A
mB
⊂
=∑ and
Pl( ) ( ),
ii
BA
A
mB
∩≠∅
=∑ are measures of uncertainty
based on the collective evidence, since Bel( ) Pl( ).
A
A≤ The
possibility theory (Zadeh, 1978; Dubois and Prade, 1998)
provides an alternative to represent uncertainties with
necessity-possibility pairs. Possibility can be regarded as a
special situation of the plausibility measure when all focal
elements Bi’s are nested. And the corresponding special
belief measure is the necessity. A random set (Molchanov,
2005) is a multi-valued mapping from the probability space
to the value space. Probability bound analysis (Ferson et al.,
2004) captures uncertain information with p-boxes which
are pairs of lower and upper probability distributions.
F-probability (Weichselberger, 2000) incorporates intervals
into probability values which also maintain the Kolmogorov
properties. Fuzzy probability (Möller and Beer, 2004)
considers probability distributions with fuzzy parameters. A
cloud (Neumaier, 2004) is a fuzzy interval with an
interval-valued membership, which is a combination of
fuzzy sets, intervals and probability distributions.
All of these forms treat variability and uncertainty
separately and propagates them differently so that each
maintains its own character during analysis. In this paper,
we take an interval-valued imprecise probability approach
for Bayesian networks to improve the robustness of
decision-making.
3 Robust BBN
One may regard an IDSS with the BBN mechanism as a
consultant that supplies various models and assessments,
combines all judgments and finally informs the user ‘if you
accept all these judgments, then you should draw these
conclusions’. In this process, robustness is concerned with
the sensitivity of the results of Bayesian analysis with
respect to the inputs.
Our proposed robust BBN is based on interval-valued
imprecise probabilities with a generalised interval form
(Wang, 2008, 2009). Traditionally, a set-based interval
{}
[,] |ab x a x b=∈ ≤≤R is a set of real numbers defined
by its lower and upper bounds. Therefore, the interval ab[, ]
becomes invalid or empty when ab>. A generalised
interval is no longer restricted to the ordered bound
condition of ab≤. This generalisation simplifies the
Bayes’ rule with imprecise probabilities and its
computation.
An interval probability captures uncertainties in
stochastic processes by simultaneously considering a set of
probabilities. The interval probability of event A is defined
as:
():[(),()] (0 ()) () 1)PA PA PA PA PA
=
≤≤≤
(1)
with its lower bound P and upper bound .P In the case
() (),PA PA= the degenerated interval probability ()PA
becomes a traditional precise probability.
The foundation of our imprecise probability is that all
imprecise probabilities are subject to a logic coherence
constraint. That is, the imprecise probabilities of event A
and its complement Ac have the relationship
() ( ) 1
() ( ) 1
C
C
PA PA
PA PA
⎧
+
=
⎪
⎨
+
=
⎪
⎩
(2)
The logic coherence constraint greatly simplifies the
probabilistic calculus structure.
For a class of decision problems, there exists a sequence
of Bayesian decision problems whose solutions converge
towards the robust solution. This holds independently of
whether the preference for robustness is global or restricted
to local perturbations around some reference model. It is
shown, that there is a sequence of Bayesian decision
problems with ever increasing risk aversion with the
associated optimal decisions converging to the optimal
robust decision (Adam, 2004). It means that, it is possible to
achieve solution which is very close to the optimal decision
even when there is no precise prior information.
Robust BBN allows us to find solutions under the
conditions when prior probabilities are not known exactly.
This solution will also be acceptable in majority of the cases
after the precise information is obtained. In other words, the
robust decision needs to be made before the precise prior
information will be available. The practical motivation
underlying the robust Bayesian analysis is the difficulty in
assessing the accuracy of prior probability distributions.
Robustness with respect to prior distributions stems from
the practical impossibility of eliciting a unique and precise
distribution. Similar concerns apply to the other elements
(likelihood and loss functions) considered in Bayesian
analysis. The main goal of Bayesian robustness is to
quantify and interpret the uncertainties induced by partial
knowledge of one (or more) of the three elements in the
analysis.
Given uncertainties involved in prior probabilities, the
estimation of imprecise posterior probabilities is based on
the generalised Bayes’ rule (GBR) (Walley, 1996; Wang,
2008)
( | )()
(|) (|)() (| )( )
CC
PB APA
PA B
P
BAPA PBA PA
=+ (3)
( | )()
(|) (|)() (| )( )
CC
PB APA
PA B PB APA PB A PA
=+ (4)
Decision support under uncertainties based on robust Bayesian networks in reverse logistics management 5
The GBR gives the lower and upper bounds of all possible
posterior probabilities given the ranges of prior
probabilities. It is used to update the initial estimation of
()PA after learning that event B has occurred. The upper
and lower probabilities, P and ,P are specified for all
subsets of the sample space. We wish to construct posterior
upper and lower probabilities (| )
P
B⋅ and (| ),PB⋅ i.e., to
update beliefs after observing the new evidence.
If there are two sources of new evidence from events A
and B, the assessment of event C can be based on a more
general structure. In the traditional BBN,
( | )( | , )()
(|,) ( | )( | , )()
( | )( | , )( )
ccc
PACPB CAPC
PC AB PA CPBC APC
PAC PB C APC
=+
⎡⎤
⎢⎥
⎣⎦
(5)
where the precise probabilities are used. We extend the
posterior probability estimation in equation (5) to consider
imprecise probabilities as
( | )( | , )()
(|,) ( | )( | , )()
( | )( | , )( )
ccc
PACPB CAPC
PC AB PA CPBC APC
PAC PB C APC
=+
⎡⎤
⎢⎥
⎣⎦
(6)
( | )( | , )()
(|,) ( | )( | , )()
( | )( | , )( )
ccc
PACPB CAPC
PC AB
PACPB CAPC
PAC PB C APC
=⎡⎤
+
⎢⎥
⎢⎥
⎣⎦
(7)
In BBN, if A and B are conditionally independent, then
equations (6) and (7) can be simplified as
(|)(|)()
(|,) (|)(|)()
(| )(| )( )
ccc
PACPB CPC
PC AB PA CPB CPC
PAC PB C PC
=+
⎡⎤
⎢⎥
⎣⎦
(8)
(|)(|)()
(|,) (|)(|)()
(| )(| )( )
ccc
PACPB CPC
PC AB
PACPB CPC
PAC PB C PC
=⎡⎤
+
⎢⎥
⎢⎥
⎣⎦
(9)
respectively.
After new evidence has taken place, we can compare if
the upper and lower probabilities of our final goal, such as
the success of a new product development project, are
increased or decreased. If it is decreased, we must respond
with a corrective action, which is able to increase the
probability of success. A collection of corrective actions
may be required. We would like to see how the final result
will be changed with different actions. For instance, in
collaborative design, the original equipment manufacturer
(OEM) makes decisions on design parameters and
configurations based on the life expectancies of components
from suppliers. Designers may need to choose one of the
available cooling fans with different sizes and speeds based
on the reliability of circuit boards from suppliers. When the
suppliers provide different sets of inconsistent data, we
make decisions based on the collective information, as well
as our past knowledge about the probability of successful
design implementation. Nevertheless, when further
information is received from suppliers, we need to respond
with corrective actions and may choose a different design. It
is important to find the optimal range of corrective actions,
which will enable us to achieve the required upper and
lower probabilities of final goal. The higher the probability
of final goal is, the higher the utility of actions performed
will be.
Upper and lower probabilities are used to compare
actions and make decisions in the following way. In Walley
(1991b), they are referred to as upper and lower provisions
respectively. A decision-maker’s lower prevision is the
highest price at which the decision-maker is sure, he or she
would bet or buy a gamble and the upper prevision is the
lowest price at which the decision-maker is sure, he or she
would buy the opposite of the gamble. Suppose that we
need to choose an action from a finite set of possible actions
{
}
12
, ,..., ,
k
aa a where the utility
()
,Ua
ω
of action a
depends on the unknown situation
ω
. We assume that
utilities are specified precisely. Otherwise, the decision
problem is much more complicated. Define a corrective
action reward j
X
by () ( , )
jj
XUa=
ω
ω
for each
1,2,..., .jk
=
To compare two possible corrective actions ai
and aj for proper decision-making, we compute the upper
and lower previsions ()
ij
P
XX− and ()
ij
PX X− based
on available information. Then, action ai is preferred to aj if
()0.
ij
PX X
−
> On the other hand, aj is preferred to ai if
()0.
ij
PX X
−
< If neither of the conditions hold, there is
insufficient information to determine the preference. The
action ai is optimal, if there is no other action that is
preferred to ai.
In Section 4, we introduce the reverse logistics and its
importance in the process of design for supply chain, before
we demonstrate decision support based on the proposed
robust BBN. The example of spacecraft circuit board
recovery in reverse logistics is given in Section 5.
4 Decision support in design for closed-loop
supply chain
The IDSS is general and can be applied in different phases
of product development. In particular, design for supply
chain is one of the under-studied research areas in
collaborative design and manufacturing. The objective of
design for supply chain is to allow engineers to consider
lifecycle costs of products from production, distribution,
maintenance, to recycle during decision-makings at the
product design phases. Engineers should make sound
decisions in selecting product platforms, configurations and
design parameters so that the costs associated with
production, transportation from multi-tiered suppliers to
OEMs, disassembly and recycling processes and
remanufacturing channels from product consumers to
OEMs.
6 E. Shevtshenko and Y. Wang
Traditionally, the study of logistics management focuses
on the forward supply chain, which is the delivery of
products from manufacturer to marketplace. Only limited
attention has been given to the reverse logistics, which is the
flow of returning products from consumer to producer. The
Council of Logistics Management published the first known
definition of reverse logistics in the early 1990s, as ‘the role
of logistics in recycling, waste disposal and management of
hazardous materials; a broader perspective includes all
related logistics activities carried out in source reduction,
recycling, substitution, reuse of materials and disposal’
(Stock, 1992). The driving force for reverse logistics has
been classified into three subgroups: economics, legislation
and extended responsibilities. It has been realised that the
total value of products returned in the US is estimated at
$100 billion annually (Stock et al., 2002).
4.1 Reverse logistics
Reverse logistics consists of planning, implementing and
controlling the reverse flow of materials and management of
related downstream information through the supply chain
with the primary purpose of recapturing value. Thus, the
associated decisions may drive a large extent of
development in the process of manufacturing and
remanufacturing, forward and backward material flows and
related operational functions (Carter and Ellram, 1998).
Reverse logistics strategies for end-of-life products are
usually developed to allow manufacturers to determine the
optimal amount to spend on buy-back and the optimal unit
cost of reverse logistics (Knemeyer et al., 2002). A good
management strategy is to find the best choices of material
recovery channels based on the conditions and values of the
used products to maximise the recoverable residual values.
Four major recovery choices are:
• Reuse: It is the process by which products are reused
directly without prior operations. It may need cleaning
and minor maintenance (e.g., reusable packages such as
bottles, pallets or containers).
• Repair: It is the process of fixing or restoring failed
products. However, there is a possibility of quality loss
(e.g., industrial machines and electronic equipment).
• Recycling: It is the process of material recovery (e.g.,
scrap, glass, paper and plastic recycling).
• Remanufacturing: It is the process of disassembly and
recovery of worn, defective or discarded products.
Disassembled products and all components are cleaned
and inspected. Those components which can be reused
are brought to inspection and those that cannot be
reused are replaced. A remanufactured product should
match the same customer expectation as new products
(e.g., mechanical assemblies such as aircraft engines
and copy machines).
Figure 1 General supply chain framework
Source: Hamza et al. (2007)
We model the closed-loop supply chain with a general
framework of the forward and reverse material flows in
PLM. This framework includes the major scenarios that can
take place in the recovering of the used product, as shown in
Figure 1. In the figure, collection refers to all activities of
rendering used products and physically transporting them
for further treatment. Sorting and inspection are the
operations that determine whether a given product is
reusable and which method to apply. Thus, sort and inspect
result in splitting the flow of used products according to the
distinct types of recovery channels such as repair, reuse,
remanufacturing and recycle.
4.2 Decision-making in reverse logistics
To support a set of decision-makers working together as a
group, a collaborative IDSS has some special technological
requirements of hardware, software and procedures (Sean,
2001). Collaborative IDSS software also needs special
functional capabilities, in addition to the capabilities of
single user IDSS software, such as anonymous input of the
user’s ideas, listing group members’ ideas, voting and
ranking of the decision alternatives. IDSS will have the
ability to take the integrated data stored within the database
and transform them through various analysis techniques.
ERP systems are able to achieve integration by bringing
together data from different sources within the corporation.
This may include disparate databases that exist across
different functional units, thus, helping the firm to gain a
more complete and realistic picture of all the data they hold.
ERP systems have traditionally not been able to provide
satisfactory support for transforming data and enabling
decision-makers to discover and learn, ultimately turning
this data into knowledge. This is where IDSS can give
strong support. The human component of group IDSS
should include a group facilitator, who leads the session by
serving as the interface between the group and the computer
systems (Shevtshenko, 2007).
Decision support under uncertainties based on robust Bayesian networks in reverse logistics management 7
Figure 2 IDSS system used for reverse logistics in the
collaborative supply chain network
IDSS of
third party
collector
ERP of distributor
companies
Data flow
Data flow Data flow
Data flow Data flow
ERP system of
supply
com
p
anies
ERP system of
retailer
companies
IDSS of manufacture
companies
Consumers
returing the
products
As shown in Figure 2, the IDSS system can be applied in
the collaborative supply chain networks to assist the
third-party collector in decision-making. First of all, the data
about the returned product are inserted into the IDSS
system. The data about returns will be transmitted to the
ERP systems of participants. Within the ERP systems, it
will be possible to track information about returned products
during the whole life cycle, until the product is disposed. It
enables the participants to be prepared for the situation
when the product should be repaired, remanufactured or
reused. Based on the historical data, the participants are able
to estimate the probability that the product will be disposed
or the new products should be produced. This information
will be used as evidences to support the decision-making.
The users of the future IDSS systems can be business
executives or some other groups of management
(knowledge) workers.
One of the challenges for decision-making in reverse
logistics management is the lack of information and
knowledge (e.g., under which working environment
products were used by customers, how they were
maintained, what the long-term impact on environment and
energy consumption will be) (Tibben-Limbke, 1998).
Therefore, risks associated with environment, health,
reusability, total cost of ownership, etc., should be
considered (Thierry et al., 1995). The amount of data related
to returned products is much less than that of new products
flowing forward in the supply chain, since, the initiator of
reverse logistics usually is end users, who are most likely to
have no motivation to keep and share detailed product
lifecycle information. Uncertainties are likely associated
with information such as the reliability of reverse material
flows, the quality and condition of returned products, the
timing of returns, the potential residual values and the
demand of the secondary market (Tan and Kumar, 2006).
Moreover, there are uncertainties which arise from limited
availability of data and deteriorated quality of data.
Therefore, reverse logistics is characterised by much higher
uncertain factors compared to regular forward material
flows in supply chains. An appropriate representation of the
uncertainties in reverse logistics is important.
Considering the high uncertainties, we can apply our
robust Bayesian networks described in Section 3 to the
selection of proper recovery channels and activities for
returned products. The IDSS enables participants to be
prepared for situations when products are ready to be
returned and decisions of recovery channel selection need to
be made. The probabilities that products are repaired,
remanufactured, reused or disposed can be used to support
decision-making.
The available information to support decision-making
for returned products is usually scarce. For this reason, the
BBN mechanism with probabilistic reasoning is a good
option in IDSS systems in reverse logistics management.
BBN can quantitatively evaluate different options and
propose what the best action could be. If the result of the
previous action is known, this piece of information can in
turn be used as extra evidence to update the probabilities for
further estimations with increased accuracy. In Section 5,
the new robust probabilistic reasoning approach is
illustrated with an example of spacecraft circuit board
recovery. The GBR theory is applied to monitor the
probability of design project being successful and the
comparison of different actions is presented.
5 Application of the robust BBNs to circuit board
recovery
We apply the robust decision-making approach to an
example of spacecraft circuit board recovery. Space systems
are inherently risky because of the technology involved and
the complexity of their activities. The significant presence
of uncertainties requires good management of risks during
the development of space systems. For example, space
shuttle is recognised as the world’s first reusable space
transportation system. The values of components are
continuously recovered and recaptured. NASA thereof is
regarded as one of the major reverse logistics practitioners.
Capturing of the uncertain conditions of these reusable
components is critical in order to prevent disasters in PLM.
Since, all phases in the spacecraft life cycle are associated
with risks, development of a robust tool to calculate the
accumulated cost and assess risks is essential in this
industry.
Figure 3 State diagram of performed tests and activities
Environmental
Test
Component
Test
Electrical
Test
Functional
Test
Recycle
Remanufacture
Reuse
Repair
Fail test
Pass test
8 E. Shevtshenko and Y. Wang
When previously used circuit boards arrive at the reverse
logistics collector, their conditions will be tested. The robust
BBN mechanism can help the collector to decide what
action should be performed to the recovered circuit boards.
After several tests, appropriate actions should be selected.
As shown in Figure 3, four tests are typically performed:
environmental test; component test; electrical test and
functional test. If the result of any test is negative, the
appropriate action including recycle, repair, remanufacture
and reuse will be performed. After the completion of any
action, the lower and upper bounds of project success
probability are updated. The decision-maker will monitor
the posterior probabilities after each action, until the
probability of project success is high enough.
The decisions must be made with the noticeable
presence of uncertainty. Not enough prior information is
available, since, the number of previous tests is small. We
would like to estimate the probability that a project will be
successful if we take an action of reuse, remanufacture or
repair for some circuit boards, i.e.,
(.. | ; .; ).P Proj Succ Yes Reuse Remanuf Repair= As the prior
probabilities and likelihood functions are given as intervals,
the posterior probabilities will also be intervals.
We calculate the range of the project success
probability. The narrower is the range, the lesser is the
indeterminacy our decision will have. The network is built
on the base of prior information. The intervals of project
success rate can be calculated according to equation (3) and
equation (4).
A simple Bayesian network example consisting of three
nodes is used here to introduce how robust Bayesian
networks are constructed, then, later in this section, a more
comprehensive network is used for further calculations. As
shown in Figure 4, relationships of environmental test,
component test and project success are built. Environmental
test is related to project success and component test is
related to both environmental test and project success. The
lower and upper bounds of prior probabilities and likelihood
functions are given in Table 1.
Figure 4 The BBN model of simple tests for project
Environmental
Test
Component
Tes
t
Project Success
Table 1 Interval prior probabilities and likelihood probabilities (where lb denotes lower bound and ub denotes upper bound) for the
Bayesian network in Figure 4
Prior probabilities and likelihood functions lb ub
P(ProjectSuccess = Yes) 0.90 0.95
P(ProjectSuccess = No) 0.05 0.10
P(Envir.Test = OK|ProjectSuccess = Yes) 0.97 0.99
P(Envir.Test = Failed|ProjectSuccess = Yes) 0.01 0.03
P(Envir.Test = OK|ProjectSuccess = No) 0.75 0.8
P(Envir.Test = Failed|ProjectSuccess = No) 0.2 0.25
P(Comp.Test = OK|ProjectSuccess = No) 0.6 0.7
P(Comp.Test = Failed|ProjectSuccess = No) 0.3 0.4
P(Comp.Test = OK|ProjectSuccess = Yes; Envir.Test = OK) 0.98 0.995
P(Comp.Test = Failed|ProjectSuccess = Yes; Envir.Test = OK) 0.005 0.02
P(Comp.Test = OK|ProjectSuccess = No; Envir.Test = OK) 0.6 0.7
P(Comp.Test = Failed|ProjectSuccess = No; Envir.Test = OK) 0.3 0.4
To calculate the two posterior probabilities
P Proj Succ Yes Env Test OK Comp Test OK== =(.. |. ; . )
and
P Proj Succ No Env Test OK Comp Test OK== =(.. |. ; . )
in the lower bound network, we use the prior probabilities
and likelihood bounds listed in Table 2.
Table 2 Prior probabilities and likelihood functions for the
nodes in the lower bound Bayesian network
Proj.Succ. = Yes Proj.Succ. = No
Prior probability of project
success
0.90 (lb) 0.10 (ub)
OK1 0.97 (lb) 0.8 (ub)
Environmental test
node probabilities
(test 1) Failed1 0.03 (ub) 0.2 (lb)
OK2 0.98 (lb) 0.7 (ub)
Component test
node probabilities
(test 2) Failed2 0.02 (ub) 0.3 (lb)
Decision support under uncertainties based on robust Bayesian networks in reverse logistics management 9
Based on equation (6), the lower bound of the posterior
probability that ‘project is successful, given that the
environmental test is OK and component test is OK’ can be
calculated as
P Proj Succ Yes Env Test OK Comp Test OK
P Env Test OK Proj Succ Yes
P Comp Test OK Proj Succ Yes Env Test OK
PProjSucc Yes
P Env Test OK Proj Succ Yes
P Comp Test OK Proj Succ Y
== =
⎡⎤
==⋅
⎢⎥
===⋅
⎢⎥
⎢⎥
=
⎣⎦
===⋅
==
(.. |. ; . )
(. | . . )
(. |..;. )
(.. )
(. | . . )
(. |..
097 098 09 0 938565505
097 098 09 08 07 01
es Env Test OK
PProjSucc Yes
P Env Test OK Proj Succ No
P Comp Test OK Proj Succ No Env Test OK
PProjSucc No
⎡⎤
⎢⎥
=⋅
⎢⎥
⎢⎥
=
⎢⎥
⎢⎥
+= =⋅
⎢⎥
===⋅
⎢⎥
⎢⎥
=
⎢⎥
⎣⎦
××
==
××+××
;. )
(.. )
(. | . . )
(. |..;. )
(.. )
... .
(. . .) (. . .)
Based on equation (7), the upper bound of the posterior
probability that ‘project is not successful, given that the
environmental test is OK and component test is OK’ can be
calculated as
(.. |. ; . )
(. | . . )
(. |..;. )
(.. )
(. | . . )
(. |..;
P Pro j Su cc No Env Te st OK Comp Test OK
P Env Test OK Proj Succ No
P Comp Test OK Proj Succ No Env Test OK
P Proj Succ No
P Env Test OK Proj Succ No
P CompT est OK Proj Succ No E
== =
⎡⎤
==⋅
⎢⎥
===⋅
⎢⎥
⎢⎥
=
⎢⎥
⎣⎦
===⋅
==
.)
(.. )
(. | . . )
(. |..;. )
(.. )
0.8 0.7 0.1 0.061434495
(0.8 0.7 0.1) (0.97 0.98 0.9)
nv Test OK
PProjSucc No
P Env Test OK Proj Succ Yes
P CompTest OK Proj Succ Yes Env Test OK
P Proj Succ yes
⎡⎤
⎢⎥
=⋅
⎢⎥
⎢⎥
=
⎢⎥
⎢⎥
+= =⋅
⎢⎥
===⋅
⎢⎥
⎢⎥
=
⎣⎦
××
==
×× + × ×
Similarly, to calculate the posterior probabilities
P
Proj Succ Yes Env Test OK Comp Test OK== =(.. |. ; . )
and
P Proj Succ No Env Test OK Comp Test OK== =(.. |. ; . )
in the upper bound network, we use the prior probabilities
and likelihood bounds listed in Table 3.
Based on equation (7), the upper bound of ‘project is
successful, given that the environmental test is OK and
component test is OK’ is calculated as
(.. |. ; . )
(. | . . )
(. |..;. )
(.. )
(. | . . )
(. |..
P Proj Succ Yes Env Test OK Comp Test OK
P Env Test OK Proj Succ Yes
P CompTest OK Proj Succ Yes Env Test OK
PProjSucc Yes
P Env Test OK Proj Succ Yes
PCompTest OK ProjSucc
== =
⎡
⎤
==⋅
⎢
⎥
=
==⋅
⎢
⎥
⎢
⎥
=
⎢
⎥
⎣
⎦
===⋅
=;. )
(.. )
(. | . . )
(. |..;. )
(.. )
0.99 0.995 0.95 0.97652
(0.99 0.995 0.95) (0.75 0.6 0.05)
Yes Env Tes t OK
PProjSucc Yes
P Env Test OK Proj Succ No
P CompTest OK Proj Succ No Env Test OK
PProjSucc no
⎡
⎤
⎢
⎥
==⋅
⎢
⎥
⎢
⎥
=
⎢
⎥
⎢
⎥
+= =⋅
⎢
⎥
=
==⋅
⎢
⎥
⎢
⎥
=
⎣
⎦
××
==
××+×× 0861
Table 3 Prior probabilities and likelihood functions for the
nodes in the upper bound Bayesian network
Proj.Succ. = Yes Proj.Succ. = No
Prior probability of
project success
0.95 (ub) 0.05 (lb)
OK1 0.99 (ub) 0.75 (lb)
Environment
al test node
probabilities
(test 1) Failed1 0.01 (lb) 0.25 (ub)
OK2 0.995 (ub) 0.6 (lb)
Component
test node
probabilities
(test 2)
Failed2 0.005 (lb) 0.4 (ub)
Based on equation (6), the lower bound of ‘project is not
successful, given that the environmental test is OK and
component test is OK’ is calculated as
(.. |. ; . )
(. | . . )
(. |..;. )
(.. )
(. | . . )
(. |..;
P Pro j Su cc No Env Tes t OK Co mp Test OK
P Env Test OK Proj Succ No
P CompTest OK Proj Succ No Env Test OK
P Proj Succ No
P Env Test OK Proj Succ No
P Comp Test OK Proj Succ No Env
=
==
==⋅
⎡
⎤
⎢
⎥
=
==⋅
⎢
⎥
⎢
⎥
=
⎣
⎦
===⋅
==
.)
(.. )
(. | . . )
(. |..;. )
(.. )
0.75 0.6 0.05 0.023479139
(0.75 0.6 0.05) (0.99 0.995 0.95)
Test OK
PProjSucc No
P Env Test OK Proj Succ Yes
P CompTest OK Proj Succ Yes Env Test OK
P Proj Succ yes
⎡
⎤
⎢
⎥
=
⋅
⎢
⎥
⎢
⎥
=
⎢
⎥
+= =⋅
⎢
⎥
⎢
⎥
=
==⋅
⎢
⎥
⎢
⎥
=
⎣
⎦
××
==
×× + × ×
Therefore, the interval posterior probabilities are
0.938565505,0.976520861
P Proj Succ Yes EnvTest OK Comp Test OK
=
==
⎡⎤
=⎣⎦
(.. |. ; . )
and
10 E. Shevtshenko and Y. Wang
0.023479139, 0.061434495
P Proj Succ No Env Test OK Comp Test OK== =
⎡⎤
=⎣⎦
(.. |. ; . )
Notice that
1
P Pro j Suc c No Env Te st OK Comp Test OK
P
Proj Succ Yes Env Test OK Comp Test OK
== =
=− = = =
(.. |. ; . )
(.. |. ; . )
which satisfies the logic coherence constraint.
If the goal of conducting the tests is to select a strategy
of board recovery so that the probability of project success
should be greater than 0.99, then environmental test and
component test are not enough. More tests are required.
Now, we move to the more comprehensive example,
where all tests are considered. Figure 5 shows the BBN
model containing all tests.
Figure 5 The BBN model for project with all tests included
Environmental
Tes
t
Component
Test
Project Success
Electrical
Test
Functional
Tes
t
Repair
Remanufacture
Reuse
Recycle
Suppose, we would like to decide what tests should be
performed in order to have a project successful rate of at
least 99%. The decision support process by the robust BBN
is illustrated step by step as follows.
Step 1 After a board passes the environmental test, we
receive the posterior probability
(
)
09160958P oj Succ Yes Env Test OK ⎡⎤
===
⎣⎦
Pr . . . . , . .
The probabilities for different actions will also be
updated as:
0 0172 0 0475P Repair Yes Env Test OK===(|.)[.,.];
0 0051 0 0187P Remanuf Yes Env Test OK===(.|. )[.,.];
08740913PReuse Yes EnvTest OK===(|.)[.,.];
0 0894 0 13P Recycle Yes Env Test OK===(|.)[.,.].
The robust BBN tool is also able to estimate the posterior
probability of project success after different actions are
successfully performed as:
(.. |. ; )
[0.275,0.382]
P Proj Succ Yes Env Test OK Repaired Yes== =
=
(.. |. ; . )
[0.959,0969];
P Proj Succ Yes Env Test OK Remanuf Yes
=
==
=
(.. |. ; )
[0.995,0.998].
P Pro j Succ Yes Env Test OK Reuse Yes
=
==
=
It can be seen that, the most preferred action to take is to
reuse the board since it has the highest probability lower
bound. The probability (.. |. )P Proj Succ Yes Env T est OK==
[0.916,0.958]
=
is not high enough to reach the target of
0.99. So we need to perform the further component test.
Step 2 If the board passes the component test, we receive
the posterior probability
(
)
[]
..;
0.973,0.983
P Proj Succ Yes Env Test OK CompTest OK== =
=
The probabilities for different actions will be also updated
as:
(|.;.)[0]P Repair Yes Env Test OK Comp Test OK
=
===
(|.;.)
[0.0051,0.0195]
P Remanuf Yes Env Test OK Comp Test OK
=
==
=
(|.;.)
[0.925,0.935]
P Reuse Yes Env Test OK Comp Test OK
=
==
=
(|.;.)
[0.0663,0.0761].
P Recycle Yes Env Test OK Comp Test OK
=
==
=
The posterior probabilities of project being successful after
taking different actions are estimated as
P Proj Succ Yes Env Test OK
Comp Test OK Repaired Yes not valid
==
===
(.. |. ;
.; )_
(.. |. ;
. ; ) [0.979,0.992]
P Proj Succ Yes Env Test OK
Comp Test OK Remanuf Yes
=
=
===
(.. |. ;
. ; ) [0.9908,0.9975];
P Proj Succ Yes Env Test OK
Comp Test OK Reuse Yes
=
=
===
It means that after a board passes the component test, the
repair action should not be taken anymore.
Since the probability
(.|. ;. )
[0.973,0.983]
P Proj.Succ Yes Env Test OK Comp Test OK
=
==
=
has not reached the required 0.99, electrical test should be
performed.
Step 3 If the board passes the electrical test, we receive
the posterior probability
(.. |. ;
.;.)[0.991,0.993]
P Proj Succ Yes Env Test OK
Comp Test OK Electr Test OK
=
=
===
Decision support under uncertainties based on robust Bayesian networks in reverse logistics management 11
The probabilities for different actions are also updated as:
(|.;
.;.)[0]
P Repai r Yes En v Test OK
Comp Test OK Electr Test OK
==
===
(.|. ;
.;.)[0]
P Remanuf Yes Env T est OK
Comp Test OK Electr Test OK
==
===
(|.;
. ; . ) [0.942, 0.944]
P Reuse Yes Env Test OK
Comp Test OK Electr Test OK
==
===
(|.;
. ; . ) [0.0566, 0.0581]
P Recycle Yes En v Test OK
Comp Test OK Electr Test OK
==
===
The posterior probabilities of project being successful after
different actions are taken are estimated as:
(.. |. ; . ;
.; )_
P Proj Succ Yes Env Test OK Comp Test OK
Electr Test OK Repaired Yes not valid
== =
===
(.. |. ; . ;
.; )_
P Proj Succ Yes Env Test OK Comp Test OK
Electr Test OK Remanuf Yes not valid
== =
===
(.. |. ; . ;
) [0.99955,0.99963]
P Proj Succ Yes Env Test OK Comp Test OK
Reuse Yes
== =
==
When the electrical test is passed, the posterior
probability of project success becomes
(.. |. ;
P
Proj Succ Yes Env Test OK==
.;Comp Test OK
=
. ) [0.992,0.995]Electr Test OK==
The probability of project being successful is high
enough to meet the minimal requirement. The result
suggests that the further functional test is not necessary.
As illustrated by the above procedure, the robust BBN
tool monitors the upper and lower bounds of posterior
probabilities until the lower bound of project success
probability is high enough. It is also possible to predict the
probability of success after every action and decide what
should be made next. This allows us to increase the
effectiveness and robustness of decision-making.
In summary, the robust BBN mechanism considers the
latest available evidence. It recalculates and updates
posterior data after new information is available. The
uncertainties can be monitored and used to estimate the
worst case scenario. The imprecise probabilities can
increase the confidence of decision-makers compared to the
traditional precise probabilistic reasoning. While,
probabilistic distributions provide more information than
deterministic estimations, interval probabilities can provide
even more information than precise probabilities.
6 Concluding remarks
In this paper, we presented a robust probabilistic reasoning
framework based on imprecise probabilities for robust
decision support. This model explicitly differentiates
uncertainty from variability and incorporates uncertainty
factors due to lack of perfect knowledge. Interval
probabilities are used to represent classes of possible
variations instead of precise ones, which captures
imprecision and indeterminacy. This allows us to consider
all possible scenarios between extreme cases during
probabilistic reasoning. A GBR was developed based on
interval probabilities such that reliable decision-making can
be supported. This robust decision support tool is useful in
PLM in collaborative networks, where lack of data and
information increases risks of decision-making. The new
approach can be used to improve the robustness of decisions
under high uncertainties in IDSSs.
Acknowledgements
E.S. would like to thank the support from the Estonian
Ministry of Education and Research for targeted financing
scheme SF0140113Bs08. The authors also appreciate Heba
Hamza for her discussions.
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