Prioritization of Product Requirements using
the Analytic Hierarchy Process
Thomas Reichel and Gudula R
¨
unger
Department of Computer Science, Chemnitz University of Technology, 09107 Chemnitz, Germany
Keywords:
Requirements Management, Prioritization, Multi-criteria Decision, Analytic Hierarchy Process.
Abstract:
The prioritization of product requirements is an essential task during the early phases of product development,
which copes with time-to-market deadlines, budgetary constraints, and personnel restrictions. Since several
decision criteria, such as cost, time, and risk, as well as the customer’s point of view and different company
divisions have to be taken into account, the prioritization of requirements corresponds to a multi-criteria,
multi-stakeholder decision problem. In this article, we propose a prioritization approach based on the analytic
hierarchy process (AHP) that creates a ranking of requirements with respect to multiple (maybe conflicting)
decision criteria and incorporates assessments of multiple stakeholders. The proposed approach overcomes
the scalability problem of AHP by using hierarchic checklists and an efficient partitioning strategy.
1 INTRODUCTION
The prioritization of product requirements is an es-
sential task during the early phases of product devel-
opment. The priority of a requirement indicates its
importance, urgency, or value for the product to be de-
veloped (Wiegers, 2003; Karlsson and Ryan, 1997).
Prioritization supports the identification of key re-
quirements of a product and, thus, helps to recognize
the key issues of product design. To cope with time-
to-market deadlines as well as budgetary and person-
nel restrictions during product development, a careful
prioritization of requirements supports the determina-
tion of valuable requirements which should be imple-
mented in a given product release (Duan et al., 2009).
Moreover, priorities of requirements help to create a
schedule that describes the order in which the require-
ments should be implemented (Pahl et al., 2007).
The point of view of different stakeholders, such
as different company divisions as well as the cus-
tomers and users of a product, should be incorporated
in the prioritization of product requirements (Karls-
son et al., 1997). With a huge number of require-
ments on the one hand and the different stakeholders
on the other hand, the prioritization of requirements is
a complex multi-criteria task that requires collabora-
tion between the stakeholders. To cope with the cog-
nitive limitations of the human mind, insufficient time
for deliberation, limited organizational resources for
information gathering, and related problem-solving
constraints (Janis, 1989), methodological support is
necessary for such multi-criteria, multi-stakeholder
decisions.
To prioritize a huge number of requirements in a
multi-stakeholder environment, we propose a prioriti-
zation approach based on the analytic hierarchy pro-
cess (AHP). The AHP, initially developed by Saaty
(Saaty, 1980), is widely applied in science and in-
dustry and its major use is the resolution of choice
problems in multi-criteria environments (Forman and
Gass, 2001). The benefits of AHP with respect to
other multi-criteria decision making methods is its
ability to incorporate intangibles (Harker, 1987), its
simplicity, ease of understanding, flexibility, and ac-
curacy (Forman and Gass, 2001). Since the traditional
AHP requires a pairwise comparison of all objects
considered (which are the requirements in our case),
the number of comparisons would grow quadratically
with the number of objects.
The contribution of this article is the utilization of
hierarchic checklists to significantly reduce the num-
ber of pairwise comparisons in the average case and
hence to overcome the scalability problem of AHP.
The next sections are structured as follows: Sec-
tion 2 presents the background of requirements man-
agement and related prioritization approaches. Sec-
tion 3 describes the AHP in detail and discusses ex-
isting approaches for the reduction of pairwise com-
parisons. The novel prioritization approach proposed
is described in Sect. 4. Finally, Sect. 5 concludes.
70
Reichel T. and Rünger G..
Prioritization of Product Requirements using the Analytic Hierarchy Process.
DOI: 10.5220/0003969600700076
In Proceedings of the 14th International Conference on Enterprise Information Systems (ICEIS-2012), pages 70-76
ISBN: 978-989-8565-11-2
Copyright
c
2012 SCITEPRESS (Science and Technology Publications, Lda.)
2 RELATED WORK
In this section, key issues of the requirements man-
agement in the mechanical and software engineering
domain as well as existing methods and tools for the
prioritization of requirements are described.
2.1 Requirements Management
Design approaches in the mechanical and the software
engineering domain, such as the VDI 2221 guide-
line (VDI, 1993; Pahl et al., 2007), the axiomatic
design (Suh, 2001), and the rational unified process
(Kruchten, 2003), emphasize an in-depth analysis of
customer needs, a transformation of customer needs
into well-defined product requirements, and finally
the creation of a product specification in the early
stages of the product development process. This pro-
cess is denoted as clarification (Pahl et al., 2007).
For a prioritization that considers the customer’s
and the manufacturer’s point of view as well as other
factors, such as legal regulations, international guide-
lines, and lately the environmental impact of prod-
ucts, a collaboration between domain experts is nec-
essary. In the mechanical engineering domain, such
a collaboration is denoted as integrated product de-
velopment (Ehrlenspiel, 2009) and plays a major role
for a successful product development project. Be-
sides this human-centered collaboration, Gumienny et
al. (Gumienny et al., 2011) emphasize the necessity
for automated information exchange and information
synthesis between the collaborating experts. There-
fore, an IT-supported prioritization that incorporates
human-centered collaboration as well as information
exchange and synthesis is favourable.
2.2 Requirements Prioritization
For the prioritization of requirements, many ap-
proaches and techniques are used in practice (Duan
et al., 2009). Simple approaches separate re-
quirements into few groups, for example demands
and wishes (Pahl et al., 2007) or functional and
non-functional (qualitative) requirements (Kruchten,
2003), or directly assign weights (important rates) to
customer needs (Ehrlenspiel, 2009). However, these
techniques primarily focus on a coarse categorization
rather than prioritization.
More sophisticated value-oriented methods com-
bine selected factors to calculate a corresponding pri-
ority. For example, Wiegers (Wiegers, 2003) pro-
poses an approach in which the stakeholders rate the
value, the cost, and the technical risk each on a scale
from 1 to 9. The priority of a requirement is then
calculated by
value
/
(cost + risk)
. In similar approaches,
for example outlined by (Wassermann, 1993) and
(Ehrlenspiel, 2009), the requirements are prioritized
during a quality function deployment (QFD) planning
process, utilizing the expected influence of customer
needs on requirements in addition to the factors value,
cost, and risk. These value-oriented prioritization ap-
proaches can help to select core requirements (Azar
et al., 2007), but do not consider the collaboration be-
tween stakeholders.
For the prioritization of large sets of requirements,
the BST (binary search tree) is proposed (Ahl, 2005).
The BST is constructed by inserting less important
requirements as left children and more important re-
quirements as right children of a given node in the
BST (similar to the sorting with a BST). Other ap-
proaches for large sets of requirements use automatic
clustering techniques and manual prioritization of
clusters for the prioritization (Duan et al., 2009; Jiang
and Eberlein, 2006). Although these approaches scale
well for large sets of requirements, a major shortcom-
ing is the lower achievable accuracy with respect to
other prioritization approaches.
Several authors suggest the analytic hierarchy pro-
cess (AHP) (Mead, 2008; Karlsson and Ryan, 1997;
Ahl, 2005; Perini et al., 2009; Regnell et al., 2001)
to achieve a consistent, highly accurate, and ratio-
scale prioritization of requirements. Since the tra-
ditional AHP approach is primarily not adapted for
a distributed prioritization with multiple stakeholders
(Regnell et al., 2001), several methods for the incor-
poration of assessments from different stakeholders
are proposed. These include simple median, arith-
metic or geometric mean calculations (Ramanathan,
2001; Saaty, 1980) and the Delphi method (Saaty,
1980; Azani and Khorramshahgol, 1990), which is
an interaction approach between stakeholders to reach
consensus. A key issue of AHP is its lack of scala-
bility, because the prioritization of n requirements re-
quires at least n · (n 1)/2 pairwise comparisons of
requirements. Several techniques for the reduction
of necessary comparisons have been proposed (see
Sect. 3.2). However, these techniques decrease the
accuracy of the prioritization resulting.
All mentioned prioritization techniques and meth-
ods are utilizable for the relevant issues, i.e., coarse
categorization, assignment of values to requirements,
and fast processing of large sets of requirements. But
they either lack support for collaboration between
stakeholders, accuracy of the prioritization, scalabil-
ity, or considering the multi-criteria environment of
requirements prioritization. The approach for require-
ments prioritization proposed in this article tries to
overcome all these shortcomings by a combination of
PrioritizationofProductRequirementsusingtheAnalyticHierarchyProcess
71
Figure 1: Example AHP criteria hierarchy for an optimal al-
ternative selection, which is choosing the most appropriate
car.
the AHP with aspects of the Delphi method and a new
technique for the reduction of pairwise comparisons.
Since the AHP is essential for this approach, it is sum-
marized in detail in the next section.
3 THE ANALYTIC HIERARCHY
PROCESS
The analytic hierarchy process (AHP), initially pro-
posed by Saaty (Saaty, 1980), is a methodology which
supports multi-criteria decisions in a widespread area
of application, e.g., optimal alternative selection, pri-
oritization, evaluation, or benchmarking (Forman and
Gass, 2001). The AHP enables a calculation of ratio-
scale weights from pairwise comparisons in a multi-
criteria environment. In the following, the major steps
of the AHP are explained in detail and existing ap-
proaches for the reduction of the number of pairwise
comparisons are discussed.
3.1 Steps of AHP
Similar to other approaches for multi-criteria decision
support, the AHP starts with the decomposition of the
problem description into subproblems, followed by
comparative assessments with respect to subproblems
and ends with a synthesis of the assessments. Fig-
ure 1 depicts an example decomposition of a selection
problem and corresponding alternatives. In general,
the AHP can be divided into five major steps.
1. Problem Decomposition and Creation of a Hi-
erarchy of Criteria. The first step of AHP is
the identification of the decision criteria of the
overall problem and the creation of a hierarchy of
the criteria. Each criterion may consist of several
sub-criteria. (Azani and Khorramshahgol, 1990)
and (Mendoza and Prabhu, 2009) suggest an inde-
pendent gathering of prospective criteria by each
stakeholder, followed by the creation of the hi-
erarchy in a joint meeting. A careful choice of
stakeholders is essential is this step, including ul-
timately affected (primary) stakeholders as well as
(secondary) stakeholders with intermediary roles.
This first step also includes the determination of
possible alternatives.
2. Pairwise Comparisons. After an identification of
possible alternatives, the pairwise comparison of
alternatives with respect to criteria on the lowest
level of the hierarchy and the pairwise compari-
son of (sub-)criteria with respect to their superior
criterion in the hierarchy starts. As a result, mul-
tiple quadratic comparison matrices are created.
In the example of Fig. 1, three 4x4 matrices, that
contain the pairwise comparisons of the cars with
respect to the criteria Quality, Purchase and Use,
and one 3x3 matrix, that contains the pairwise
comparisons of Quality, Purchase and Use with
respect to the overall selection problem, are cre-
ated. Each pairwise comparison is rated on an in-
terval scale from 1 (both comparison objects (i.e.,
alternatives or criteria) are equal with respect to
the superior criterion) to 9 (the first comparison
object extremely dominates the second object with
respect to the superior criterion). With the recip-
rocal values
1
/
9
,...,1, a lower assessment of the
first object can be specified.
3. Validation of the Consistency of Pairwise Com-
parisons. The rate of consistency is measured by
the consistency ratio CR for each comparison ma-
trix (Saaty, 1980). The CR is calculated based on
the maximal eigenvalue of the matrix. The ratio is
equal to zero for an ideal comparison matrix and
greater than zero for inconsistent matrices. Saaty
proposes a consistency be satisfying, if CR is less
than 0.1.
4. Calculation of Local Weights. For each com-
parison matrix the local weights are calculated. A
local weight specifies the assessment of a compar-
ison object with respect to the superior criterion in
the interval [0,1]. The local weights are defined to
be the values of the first eigenvector of the com-
parison matrix which is calculated based on the
maximal eigenvalue of the matrix (Saaty, 1980).
5. Synthesis of Global Weights. The global weights
of alternatives (i.e., the priorities) are calculated
based on the local weights. For each alternative
the local weight of the alternative and the global
weight of the corresponding criterion are multi-
plied. These results are summed for all criteria
on the lowest level of the hierarchy in order to
calculate the global weight of an alternative. The
global weight of a criterion v
j
on the lowest level
of the hierarchy is calculated by multiplying the
local weights of the criteria on the path between
v
j
and the overall problem description (i.e., the
root of the hierarchy).
ICEIS2012-14thInternationalConferenceonEnterpriseInformationSystems
72
Figure 2: Examples for organizing requirements in hierarchical form. Left: Assignment to functionalities. Middle: Assign-
ment to responsible company departments. Right: Assignment to life cycle phases.
3.2 Existing Approaches for the
Reduction of Pairwise Comparisons
Wedley et al. (Wedley et al., 1993) states that there
are only n 1 comparisons necessary for the calcu-
lation of the local weights of n comparison objects.
The remaining comparisons are derived from the n1
comparisons. Based on a case study, the authors rec-
ommend to compare all objects with the object with
the lowest (assumed) rank to achieve the minimum
inconsistency.
Since redundant comparisons are necessary to
check the assessments and to measure the consistency,
Harker (Harker, 1987) proposes so-called local stop-
ping rules. These rules require further comparisons
(beyond Wedleys n 1 comparisons) only if a next
comparison can significantly contribute to the cur-
rent local weights. An extension of this approach,
described by Millet and Harker (Millet and Harker,
1990), introduces so-called global stopping rules that
take the entire decision hierarchy into account. Com-
parisons of a specific branch in the criteria hierarchy
are performed only if the entire branch significantly
contributes to the global weights of the alternatives.
Another (local) approach is proposed by Shen et
al. (Shen et al., 1992) who suggest the partitioning
of the set of comparison objects into groups which
have one comparison object in common. While the
weights of the comparison objects in the groups are
determined with the traditional approach, the weights
for the entire set are directly derived from the group
weights and the weight of the common object.
Weiss and Rao (Weiss and Rao, 1987) propose
the so-called use of incomplete experimental design
in which each stakeholder compares a subset of the
hierarchy only and, thus, the number of comparisons
is reduced for each stakeholder. The authors also sug-
gest the deletion of certain attributes in order to re-
duce the size of the AHP hierarchy a priori.
The approaches mentioned reduce the number of
comparisons in arbitrary AHP decision problems and
accept a minimum increase of inconsistency. In con-
trast, the approach for the reduction of pairwise com-
parisons proposed in this article tries to preserve the
accuracy of the global weights. Furthermore, the
approach proposed can be combined with the ap-
proaches outlined in this section.
4 AHP APPROACH FOR THE
PRIORITIZATION OF
REQUIREMENTS
The requirements prioritization approach proposed in
this section utilizes the AHP to incorporate multiple
criteria and multiple stakeholders for the prioritiza-
tion of requirements. The approach provides tech-
niques for the effective reduction of necessary pair-
wise comparisons of requirements based on the hier-
archic structuring and partitioning of requirements.
4.1 Hierarchic Structuring of
Requirements
A partitioning of requirements into groups with sim-
ilar concerns is often used to manage a huge number
of requirements. As described by (Pahl et al., 2007;
Ehrlenspiel, 2009; Kruchten, 2003), tree structures
are appropriate for such a partitioning. A partitioning
according to the major functionalities of the product
(Fig. 2, left) is frequently used, because functionali-
ties can (hopefully) be developed independently and
integrated afterwards (for example specified by the
V-model (Boehm, 1979; VDI, 2004)). Pahl/Beitz
(Pahl et al., 2007) propose so-called partial require-
ments lists that contains requirements related to dif-
ferent company departments (Fig. 2, middle). Since
life cycle oriented development becomes mandatory
for technical products, also a partitioning into life cy-
cle phases can be helpful to structure requirements
(Fig. 2, right). Because of cross-cutting concerns,
PrioritizationofProductRequirementsusingtheAnalyticHierarchyProcess
73
requirements may belong to more than one concern
and, thus, should be part of several groups of require-
ments (e.g., Req 2 in Fig. 2). For example, the require-
ment ”increase energy efficiency”, may belong to the
life cycle phases manufacturing, use, and recycling as
well as to several company departments, such as mar-
keting, management, and Research & Development.
Ehrlenspiel (Ehrlenspiel, 2009) and Pahl/Beitz
(Pahl et al., 2007) incorporate life cycle, organiza-
tional, and functional aspects of product requirements
in order to create a hierarchic structure. These check-
lists contain general aspects of a product to be devel-
oped and can be used to validate the completeness of
a requirements specification as described in (Reichel
et al., 2011).
For the requirements prioritization with AHP, we
propose to use checklists to efficiently reduce the
number of pairwise comparisons by utilizing the tree
structure of the checklist as criteria hierarchy (step 1
of the AHP). For each criterion on the lowest level of
the hierarchy, only the requirements that are directly
related to the criterion are rated (step 2 of the AHP).
The local weights of the requirements that are not re-
lated to the criterion are assumed to be zero. This as-
sumption is reasonable, since all requirements that are
not related to a criterion should be prioritized as low
as possible when only this criterion is considered. The
modified assignment of alternatives to criteria on the
lowest level of the hierarchy extends the conventional
AHP approach with the goal to reduce the number of
pairwise comparisons while preserving the accuracy
of the priorities resulting.
4.2 Prioritization of Requirements
The prioritization of requirements start with the de-
termination of a criteria hierarchy as described in
Sect. 3.1 (step 1) in order to decompose the overall
prioritization problem. The prioritization utilizes a
checklist described in Sect. 4.1 as criteria hierarchy,
since it provides the necessary problem decomposi-
tion. If such a checklist is already used for the pre-
ceding clarification of requirements, as proposed in
(Reichel et al., 2011), the reuse of the checklist for the
prioritization is beneficial, especially because the hi-
erarchic structure of the checklist (i.e., the criteria hi-
erarchy) is determined by all stakeholders concerned
and the product requirements are already assigned to
the corresponding checklist items (i.e., criteria).
If a checklist is not used in the requirements clari-
fication so far, it has to be created by all stakehold-
ers concerned. The creation process of a checklist
highly depends on the product type and the num-
ber of stakeholders involved. For a small number of
stakeholders, an informal meeting can be sufficient
to create the criteria hierarchy. However, for large
groups a methodological approach, such as the Del-
phi Method (Azani and Khorramshahgol, 1990) or a
value-based multi-stakeholder approach as described
by (Mendoza and Prabhu, 2009), is recommendable
to obtain the point of view of all stakeholders. After
the creation of the criteria hierarchy, all requirements
have to be assigned to corresponding (sub-)criteria.
With a huge number of requirements to be assigned it
is feasible that the stakeholders assign subsets of the
requirements simultaneously. Since the assignments
have a strong impact of the priorities resulting, all as-
signments should be reviewed by other stakeholders.
In the next step of the prioritization, pairs of re-
quirements and pairs of criteria are compared. This
step starts with the pairwise comparison of require-
ments with respect to the criteria of the lowest level,
followed by the pairwise comparison of criteria with
respect to their superior criterion. As proposed by
(Forman and Gass, 2001; Schoner and Wedley, 1989),
this bottom-up approach should be used if the in-
dependence of requirements and higher-level criteria
could not be assured, i.e., the weighting of higher-
level criteria depends on the given requirements.
In order to limit the number of pairwise compar-
isons for each stakeholder on the one hand and to
achieve a high accuracy of the prioritization on the
other hand, two strategies are used for the compar-
isons.
1. Partitioning. In the partitioning strategy, differ-
ent groups of stakeholders compare different sets
of requirements with each other. The strategy is
primarily used to reduce the number of compar-
isons for individual stakeholders and to transfer
pair comparisons of requirements of a similar do-
main to the corresponding domain experts. The
partitioning strategy may decrease the accuracy
of the prioritization, since not all stakeholders are
involved in the comparison of all requirements.
However, a pairwise comparison of requirements
related to a specific domain by an expert not fa-
miliar with the domain may also decrease the ac-
curacy. This strategy corresponds to the use of in-
complete experimental design by Weiss and Rao
(Weiss and Rao, 1987) for the prioritization of re-
quirements.
2. Consensus. In the consensus strategy, a group of
stakeholders (e.g., experts of different domains)
assess the same set of requirements (or criteria)
independently. For this well-known strategy, we
propose to use the following indicators to deter-
mine a significant deviation of stakeholder com-
parisons.
ICEIS2012-14thInternationalConferenceonEnterpriseInformationSystems
74
(a) The pairwise comparisons of two stakehold-
ers result in different orders (ranks) of the local
weights of the compared objects;
(b) The euclidean distance of the local weight
vector of the criterion is above a user-defined
limit;
(c) A sensitivity analysis determines, that the de-
viation of stakeholder comparisons has a sig-
nificant influence of the priorities resulting (the
sensitivity analysis in AHP determines the in-
fluence of single pairwise comparisons on the
global weights).
While the indicators (a) and (b) can be calculated
based on the given local weights, the indicator (c)
requires pairwise comparisons for the entire hier-
archy to calculate the priorities resulting.
The independent comparisons are either unified
using the geometric mean proposed by (Mc-
Carthy, 1992) or, if the indicators exceeds a user-
defined limit, an additional interaction between
the stakeholders to achieve consensus for the par-
ticular comparisons is necessary. This strategy is
primarily applied to consolidate the accuracy of
the prioritization with respect to all stakeholders.
We propose the usage of the partitioning strat-
egy for the comparison of requirements by the cor-
responding domain experts. Therefore, the task of
pairwise comparisons of requirements with respect to
criteria on the lowest level is distributed among the
domain experts. The following pairwise comparisons
of criteria with respect to the corresponding higher-
level criteria is done by using the consensus strategy.
After the completion of the pairwise comparisons,
a consistency check, according to step 3 of the AHP,
validates the consistency of the comparisons. If an
inconsistency is found (i.e., a consistency ratio above
0.1), the comparisons have to be revised by the cor-
responding stakeholder. The comparison matrices
which are created with a consensus strategy by differ-
ent stakeholders have to be unified as described in the
consensus strategy. An exceeding deviation not nec-
essarily implies that the geometric mean of dissonant
comparison matrices is not sufficient for the unifica-
tion of the matrices, but the corresponding stakehold-
ers should be aware of deviant comparisons and be
potentially able to correct the comparisons.
The final steps of the requirements prioritization
are the determination of local and global weights
(steps 4 and 5 of the AHP). According to Sect. 4.1, the
local weights of requirements with respect to criteria
on the lowest level of the hierarchy are determined by
calculating the eigenvector of the corresponding com-
parison matrix for related requirements and by assum-
ing a weight of zero for unrelated requirements. The
eigenvector method is also used for the determination
of all local weights of criteria with respect to their
higher-level criterion. Based on the local weights the
global weights, i.e., the priorities of the requirements
are determined as described in Sect. 3.1.
When requirements are modified after the comple-
tion of the prioritization, the corresponding compari-
son matrices have to be revised by the stakeholders
assigned. If the modification of requirements also af-
fects the assessment of related criteria, the compari-
son matrices of the superior criteria have to be revised
additionally.
The determination of the criteria hierarchy as well
as the determination of the relations between require-
ments and the criteria on the lowest level of the hi-
erarchy are the crucial decisions for the achievement
of valid priorities. Therefore it is arguable whether a
checklist hierarchy utilized during the clarification of
requirements (as described in Sect. 4.1) can always be
applied for the requirements prioritization. An adap-
tion of the hierarchy may be necessary. However, the
relations between requirements and checklist items
(i.e., criteria) created in the clarification are highly
consistent, since the relations are already utilized to
validate the completeness of requirements specifica-
tions (Reichel et al., 2011).
5 CONCLUSIONS
The approach for the prioritization of requirements
proposed in this article utilizes the analytic hierarchy
process (AHP) for an efficient and precise determina-
tion of priorities. The overall prioritization problem
is decomposed into subproblems that require the pair-
wise comparison of requirements with respect to sin-
gle decision criteria of the overall problem. Due to
this decomposition, multiple domain experts can par-
ticipate in the process, either by weighting require-
ments and criteria of their own domain only or by
weighting requirements and criteria in a corporate de-
cision to achieve consensus. We propose several in-
dicators for the determination of a significant devia-
tion of expert assessments. In addition to both strate-
gies for the incorporation of experts, an approach for
the reduction of necessary pairwise comparisons of
requirements is proposed. The reduction approach is
based on the assumption that local weights are equal
to zero for requirements which are not related to cri-
teria on the lowest level of the AHP hierarchy. The
prioritization approach proposed improves the scala-
bility of the AHP and, thus, can be applied for the pri-
oritization of medium and large sets of requirements.
PrioritizationofProductRequirementsusingtheAnalyticHierarchyProcess
75
ACKNOWLEDGEMENTS
The Cluster of Excellence “Energy-Efficient Prod-
uct and Process Innovation in Production Engineer-
ing” (eniPROD
c
) is funded by the European Union
(European Regional Development Fund) and the Free
State of Saxony.
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