Supporting make or buy decision for reconfigurable manufacturing system, in multi-site context Youssef BENAMAa*, Thècle ALIXb, Nicolas PERRYc a
University of Bordeaux, 12M, UMR5295, F-33400, France University of Bordeaux, 1MS, UMR-CNRS 2518, F-33400, France c Arts et Métiers ParisTech, 12M, UMR5295, F-33400, France
b
*
Corresponding author. Tel.: +33-556-845-402; fax: +33-556-845-436. E-mail address:
[email protected]
Abstract
When designing new production system, one important decision is to identify which components of the end-products will be manufactured by the system, and which of them will be externalized. According to this decision, Necessary operations and machinery are identified allowing design of production system . In the case of reconfigurable production system operating in multi-context environment, when analyzing the make or buy decision model , additional constraints should be considered. This paper aims to provide a structured make or buy decision model, adapted for reconfigurable manufacturing systems with strong mobility constraints. Industrial application case is provided to illustrate the presented method. Reconfigurability, RMS, make or buy, multi-site context, MCDM.
I.
Introduction The make or buy decision problem, also known as "sourcing", "outsourcing" or subcontracting", is among the most pervasive issues confronting modern organizations (PADILLO and DIABY 1999). Making the right decision with regard to outsourcing can provide a major boost to a company's financial performance, although there is evidence that many companies do not achieve the advantages of outsourcing.(van de Water and van Peet 2006). (R. T. McIvor, Humphreys, and McAleer 1997) deonstrate that many decisions on outsourcing are rarely taken on the basis of particular strategic perspectives. Most of time the only intention is gaining short-term cost advantages(van de Water and van Peet 2006) In the following sections we will conduct a literature review on RMS. Next, we discuss existing frameworks for make or buy decision . Then we will detail our proposed make or buy model adapted for RMS systems. Finally we will conclude and present further works.
II.
Reconfigurable Manufacturing Systems review Manufacturing systems operating in a context characterized by: demand fluctuation, local production and site dependency, should cope with specifications such as mobility, scalability and functional adaptability. Those
specifications allow fast and cost effectively adaptation to environment changes. In the literature, manufacturing systems meeting these specifications are referenced as Reconfigurable Manufacturing Systems (RMS). III.
Make or Buy existing frameworks
The "make or buy" is a strategic decision and has implications for the overall corporate strategy of the organization by analyzing a number of strategic factors in case of short term cost reduction propose, longer-term strategic considerations, which have greater importance, should be considered (Öncü, Oner, and Başoğlu 2003). A company's degree of vertical integration will be the result of make or buy decisions accumulated over times (PADILLO and DIABY 1999). (PADILLO and DIABY 1999) identified six diverse disciplines covered by the make or buy problem : (1) industrial organization; (2) corporate/business strategy; (3) purchasing or supply management (4) strategic operations management; (5) operations research; and (6) cost accounting or managerial economics. Make or buy decision was argued most frequently by the economists. The economists have considered the "make or buy" problem especially with the perspective of costs. But the "make or buy" decision considerations should not only focus on costs(Öncü, Oner, and Başoğlu 2003). Many authors, have
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noted the need to include multiple factors when performing a make or buy analysis(PADILLO and DIABY 1999).(PADILLO and DIABY 1999) takes into account strategic competitive performance, managerial performance, sourcing performance and financial performance. (Ronan T. McIvor and Humphreys 2000) proposed a model based on technical capability, comparison of internal and external capabilities, organization profiles and total acquisition costs. Nevertheless, in area of reconfigurable manufacturing systems, we notice a lack of models that takes into account the production system mobility. Furthermore, in multi-site context, the longer term vision should be incorporated into the decision model IV.
Mathematical tools for decision analysis
IV.1. desirability functions desirability functions are value functions which express the level of satisfactions of decision maker for attributes values according to the decision requirements and his expectations. They are non dimensional, monotonous, or piecewise functions, whose values are ranged in the interval [0,1]. A desirability d=0 represents an unacceptable property value, whereas a desirability d=1 represents a completely acceptable property (Quirante 2012).
choice preference between solutions is simplified (Collignan 2011). V. The proposed make or buy model for RMS systems V.1. a three model stages : The proposed decision model framework is adapted from the model proposed by (van de Water and van Peet 2006). This framework highlights 3 decision model stages.: Strategic Analysis In our analysis, the strategic stage deal with the importance, also named weight, of each indicator. The given importance highlights the priorities of the decision maker. Decision situation has an impact on the priorities, for example, considering the purchasing situation classification presented by (Faris et al. 1967). Alternative evaluation This stage proposes a model to evaluate either alternatives in house manufacturing or external sourcing. The decision
decision making situation product importance
Stage 1 : Strategic Analysis
decision indicator importance
complexity
IV.1.1. Harrington function Function desirability proposed by [Harrington, 1965] is given by the expression: in the case of One-sided decreasing function (figure 1) :
Figure 1 : IDEF0 model of strategic analysis stage
model is based on indicators definition. Each of the four indicators proposed is depending on other parameters which we call attributes. Figure 4 shows a description of the evaluation model structure.
The decision maker should specify two limits : Soft limit (SL): indicates the limit below which the satisfaction is maximal. indicates the corresponding satisfaction level. Accurate constraint (AC): indicates the limit above which the satisfaction is minimal. indicates the corresponding satisfaction level.
Providers selection
Decision maker preferences (stage 1)
Stage2 : Alternatives Evaluation
Alternatives classification regarding objectives
Alternatives evaluation
Figure 2 : IDEF0 model of Alternative evaluation stage
Figure 3: One-sided decreasing function proposed by (Harrington,1965)
IV.2. Aggregation function Aggregation functions allow to convert multi-objective problem to mono-objective problem, in which expression of
This stage is about contractual aspects in providers selection process and collaboration nature definition. It's based on previous stage results. While our aim is to identify if manufacturing of a specified product while be achieved in house or via external sourcing, the results of the present stage is out of this paper scoop. VI.
Alternative evaluation model:
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Technical-economical objective
Objectives
Attributes
cost
Risk Objective
socio-economical objective
Technical capability
Supply cost Technical Feasibility
Local employment creation
On site storage cost Technical capacity
supply dirupti on risk
On site transformation cost
Alternatives
S2 : external sourcing
S1: in house manufacturing
Figure 4 : alternatives evaluation model structure
In this section we conduct a comprehensive description of the decision model used to evaluate each solution ( make or buy). we describe how to build each objective, then how evaluate its corresponding satisfaction value. Next, we explain aggregation model to obtain local performance for each production site, and finally how to extract the global performance that will be used to argue the decision of make or buy. VI.1. Assessment of Technical economical Objective VI.2. cost evaluation Cost objective reflects the overall cost resulted from using an alternative. It's obvious that in both situations make or buy, costs estimation don't use the same elements. We identify three attributes linked to cost objective :
o
investment, costs relative to usual functioning like process configuration cost, maintenance cost, consumed energy cost. In addition, for a reconfigurable manufacturing system, machines are shipped on site, so it's necessary to take into account the shipping cost of machines. external sourcing case : in this case, on site operations concern in most cases quality inspection operations when receiving materials, and sometimes reworking operations. In site transformation cost, in the case of external outsourcing, concerns quality costs.
VI.2.4. Cost objective satisfaction evaluation Evaluation of the cost objective satisfaction is based on satisfaction function. We use the One-sided decreasing function proposed by (Harrington,1965). VI.3. technical capability objective
VI.2.1. supply cost : supply cost attribute evaluates overall cost inherent to supplying all necessary component until the final site localization. Supply cost takes into account material purchasing costs and shipping costs set from transportation costs and customs clearance fees. VI.2.2. on site storage cost Once arrived onsite, materials should be stored for a period. Storage activity generates cost. This attribute depends on component value, storage period and cost of all tools used in storage activity. VI.2.3. on site transformation cost transformation cost attribute concern all costs linked to transformation operations and value added activities realized on site. either in house manufacturing or external sourcing alternative don't require the same operations. in consequent, evaluation of transformation cost attribute is adapted for each case : o in house manufacturing case : In this case, on site transformation operations require machinery operations. Resulted transformation cost take into account, machinery
Technical capability considers the ability of the alternative, i.e. Make or buy to, first, respect the required product quality. secondly, be able to satisfy demand volume. Consequently, Technical capability will be described by two factors : Technical feasibility and technical capacity. In order to evaluate technical feasibility and technical capacity, distinction must be made between internal and external technical capability. VI.3.1. Internal technical feasibility In the case of in-house manufacturing, technical feasibility described the ability of in-house manufacturing to ensure the know-how and process required to satisfy the product feasibility on site. Technical feasibility depends firstly on the system mobility: in order to be able to produce on client site the production system should be movable from each site to another. In consequent, system mobility is critical to determine the internal technical feasibility. Furthermore, manual operations are used in the manufacturing process. Therefore, to reduce manufacturing costs, operators are needed to be hired locally on production site. Since the system is destined to produce on the final client site, and should change the production localization with every new command,
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R&D and design capability are embedded in Technical feasibility. In the other hand, manufacturing capability, speed of development and NPI rate determine the technical capacity of suppliers.
Internal technical capability
Technical feasibility
Technical capacity Supplyin g capacity
Production localization
Energy availability
Competence availability
System mobility
Availability of suppliers
Providers’ proximity
Figure 6 : internal technical capability factors
the needed qualification availability should be taken into account and that, for each new production localization. In consequent qualification availability is a second critical condition for internal technical feasibility. On the other hand, in the special context of solar energy, the final products are destined to be installed in desertic localization where energy accessibility is always difficult. Energy availability and accessibility should be also taken into account.
VI.3.2. Internal technical capacity Internal technical capacity aims to verify that make alternative can respect the required volume demand. The ability to supply the necessary quantity of raw materials required to manufacture products on site. Two factors are involved in supplying capacity. First, the availability of qualified suppliers and their proximity from the geographical production localization. VI.3.3. Supplier technical capability McIvor and Humphreys(Ronan T. McIvor and Humphreys 2000) identified 6 criteria to evaluate the technological capabilities of supplier, which include manufacturing capabilities, technical support, design capability, investment in R&D, speed of development and new product introduction (NPI) rate. In our analysis, Technical support, investment on
VI.3.4. evaluation of technical capability satisfaction The notation of each capability technique factor is realized by giving notation between 0 and 1. When considering make or buy alternative, satisfaction of each corresponding factor of technical capability is obligatory. The failure of one technical capability factor could not be compensated by the well performance of other technical capability factor. In consequent, non-compensatory aggregation strategy is needed. Satisfaction value of the technical capability objective is then given by using the Generalized OWA Aggregation operator. VI.4. socio-economical objective In the case of public projects, where clients are governments or official institutes, socio-economical issues must be considered. (Öncü, Oner, and Başoğlu 2003) stated that " A government concerned with economic growth cannot ignore the economic aspects of technology. Major purpose of national technology policy is the harnessing of technology to meet economic and social goals[...] When one localmanufacture project is chosen rather than an import project, the choices have consequences for employment, [...]. Each local manufacture project will affect employment and wage payments."(Öncü, Oner, and Başoğlu 2003) It's obvious that the socio-economic benefits in terms of promoting local employment have an impact on the decision. We propose to incorporate in our model this socio-economical objective, which is concerned with the direct employment creation. This socio-economical objective will be directly linked with geographical production localization of the supplier. Thereby the satisfaction value of this socioeconomical objective depends on the localization, if the supplier is localized in the same country than client site, the satisfaction value is 1, otherwise, the satisfaction value is 0.1.
Technical capability of supplier
VI.5. Assessment of technical and economical objective : Technical feasibility
Technical capacity
Design capability
Manufacturing capability
For a considered make or buy alternative, the assessment of the corresponding technical and economical objective is based on the aggregation of cost, technical capability and
Technical support
Speed of development
VI.6. Risk Objective
Investment on R&D
NPI rate
VI.6.1. Identification of risk factors
Figure 5 : technical capability factors for supplier evaluation
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supply disruption risk strikes at the supplier plant supllier financial instability
Appropriation risk
shutdowns in the event of catastrophe
Technology diffusion risk
purchase price ( supplier opportunistic behavior)
Loss of confidentiality of a particular value-creating asset by entering into a sourcing relationship with an outside supplier
political instability in the supplier's country Switching costs ( specialization)
Factors of risk
Ecological environment Transportation activity
intermodal transfer Operations (break of load)
socio-cultural environment Legal environment Human failures
economical environment
product degradation risk
Machinery failures
political environment
implantation site risk
Internal risk
Figure 7 : Identification of risk factors
(PADILLO and DIABY 1999) recognize that any internal or external sourcing relationship carries a level of risk for the firm which depends upon the nature of the transaction in question, the relationship of the firm with its supplier, and the stability of the supplier. (PADILLO and DIABY 1999) identified 4 sourcing risk attributes :appropriation risk, technology diffusion risk, end-product degradation risk, and supply disruption risk. Appropriation and technology diffusion risks are relevant mostly for outsourcing alternatives. While Supply disruption is applicable to both inhouse and outsourcing alternatives (PADILLO and DIABY 1999). On the other side, end-product degradation risk is in relation with the outsourcing of an activity that is located between the firm and its customers. This type of risk is not present in our problem, but the risk about transportation activity remains dominant. (Wagner and Bode 2008) divided risk sources into five distinct classes: (1) demand side (2) supply side; (3) regulatory, legal and bureaucratic; (4) infrastructure; and (5) catastrophic. According to authors, " while the first two risk source categories deal with supplydemand coordination risks that are internal to the supply chain, the latter three focus on risk sources that are not necessarily internal to the chain". (Srinivasan, Mukherjee, and Gaur 2011) focus on two types of factors that can impact the performance of supply chain , the first factors are internal to supply chain, which are demand and supply risks, like demand variability, lead-time variability supply delays, order cancellations, etc.). on the other hand, environment uncertainty which includes factors that are external to the supply chain. Those factors are strategic in nature, like, changes in product or process technology, competitor behavior, changes in consumer tastes and preferences, etc. They noted "Supply and demand risks can usually be estimated using probability or likelihood estimation but
environment uncertainty cannot be estimated."(Srinivasan, Mukherjee, and Gaur 2011). Production system mobility implies that the characteristics of the site where the production system will be implanted, will vary. In consequent, the implantation site risks should be integrated in the analysis. We use a macro-environment analysis, like the PESTLE approach (Kolios and Read 2013) to characterize risks related to the implantation site. In the other hand, either make or buy situations require realization of additional operations by the buying firm. In the case of outsourcing alternative, internal operations correspond to material reception control tasks. Thos operations should take place locally on the implantation site. In the case of make alternative, internal operations correspond to all necessary operations that will ensure the realization of the considered product or component by the firm. In the both cases, internal operations need human and machinery interventions and should be realized locally on implantation site. In consequent, internal risks corresponding to human and machinery failures should be considered in both situations.
VI.6.2. Assessment of risk objective The assessment of each risk factor is firstly conducted using the FMECA( Failure Modes, Effects and Criticality Analysis). Each risk factor will be identified and quantified in term of likelihood of occurrence and in term of severity, in order to assess the criticality of the risk factor. Thereby, the risk criticality of the make or buy alternative will be defined by summing the corresponding criticality of risk factors. The next question is how to decide if the level of the risk criticality is acceptable or not. For this, we define a satisfaction function that will express the preferences of the decision maker. We use Derringer function (Derringer,1980);
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the DM expresses an interval of criticality levels among which the criticality level of the considered alternative will be acceptable. In fine, the assessment of the risk objective is expressed by value between 0 and 1, with 0 means unacceptable solution, and 1 corresponds to a fully satisfactory solution. VI.7. Performance evaluation In a multi-site context, make or buy decision should be made considering the overall sites where production will be operated. Evaluation of objectives is made for each site, then, global decision is taken considering overall sites performance. VI.7.1. Local Performance evaluation Local performance evaluation aims to find out the best alternative, make or buy, for each considered site localization. Each objective is evaluated as it was mentioned previously. On the other hand, decision-maker should express it's preference between the importance of each objective. Judgment is conducted using pairwise comparison. Other point linked to preference of decision maker is the compensation between objectives. Depending of decision situation, is the decision maker wants to make a trade-off between meeting the 4 objectives, or not?. In order, to allow this liberty to the decision maker, we choose to aggregate the local performance evaluation by using the GOWA operator. Thereby, the decision maker will set the trade-off strategy parameter to decide if compensation will be considered or not. For each alternative j, local performance evaluation for site i is given by this expression : TEO : Technical and Economical Objective value RO : Risk Objective value VI.7.2. Global Performance evaluation Global Performance evaluation aims to determine the best alternative in regard to overall sites. First condition that should be verified is the importance of each site. For strategic reasons, like the willingness to enter a new market, or for reasons of market size. Thereby global performance evaluation will be obtained by weighting each by the importance of the site i. Depending on decision situation and firm's strategy, compensation of performance between different site may be considered or not. We use the GOWA operator, in order to allow this freedom to the decision maker. Global Performance Evaluation (GPE) of the alternative j is given by the following expression:
n is total number of sites where the production system will operate. is the importance of the site i. is the local performance evaluation of the alternative j, for the site i. s is the trade-off strategy parameter. All alternatives will be ranked following the GPE value, and then The best alternative will have the high GPE.
VI.7.3. Impact of the strategic decision on the choice of the aggregation strategy At a local level, i.e when looking for the optimal solution for one location, compensation between the technical and economical factors might be done, but compensation can't be made between TEO and Risk Objective. At global level, the trade-off of the aggregation strategy depends strongly on the financial and strategic forecasts of the firm. Compensatory aggregation strategy means that compensation might be done between sites. In consequent, firm has included in his financial projections that one or more sites may have deficient results that will be compensated by the results of others sites. Table 1Aggregation strategy and decision level
Level
Local (i.e. for 1 site)
Aggregation strategy
Compensation between TCO
VII.
Risk Objective can't be compensated
Global (for n sites) Depends on firm's strategy
Industrial application VII.1. context and hypothesis
The Industrial application concerns an enterprise E, operating in solar energy sector. For confidentiality reasons, real values have been changed, but hypotheses and assumptions remain valid. The component analyzed is a steel part obtained by bending process. This part is critical because it contributes to mechanical resistance of the end-product. The production should be operated by the same reconfigurable manufacturing system sequentially on 5 different sites. The expected volume demands are : Table 2 : expected volume demand
Site Expected volume demand (parts)
S1 20000
S2 18000
S3 16000
S4 5000
S5 11000
Enterprise design both the product and the reconfigurable production system that will manufacture and assemble the end-product on site. Decision to make or buy this component is important in order to design the production system. We will consider 3 different alternatives: Alternative 1 (A1) : part will be manufactured by the internal production system. This corresponds to the make scenario. Alternative 2 (A2): part will be realized by an external supplier localized in Eastern Europe. Alternative 3 (A3): part will be realized by an external supplier localized in North Africa, where first installation can take place.
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VII.2. stage 1: Strategic Analysis
VII.3. stage 2: Evaluation of Alternatives
Decision-maker expresses its preference concerning those points : Objective's weighting Importance of each objective is set using a pairwise comparison. A scale of 1 to 9 is used as proposed by (Saaty 1990). In order to avoid inconsistency when weighting objectives, a consistency indicator may be used. minima threshold is required to ensure that pairwise matrix is consistent. Saaty proposed a threshold of 0.1 (Collignan 2011). Therefore, the importance of each objective will be obtained by the eigenvector of the matrix. Table 3 : judgment matrix to set importance of objectives Cost Objective Cost Objective Socio-econ. Obj.
1/6
3
6
Alternative 1 Alternative 2 Alternative 3
Site 1 9,25 € 4,98 € 6,25 €
Site 2 9,02 € 4,81 € 5,89 €
Site 3 8,15 € 5,28 € 5,05 €
Site 4 9,16 € 7,00 € 5,32 €
Site 5 8,38 € 5,36 € 4,82 €
We used satisfaction function proposed by Harrington as detailed previously. For the decision-maker, acceptable unit costs should range between 4€ and 10€. We use those values to set the satisfaction function : Table 7 : Harington function parameters
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SL 4
1/5
inconstancy =0.09 Table 4 :priorities of each objective Cost Objective
Technical capability
Socio-economical objective
0.635
0.287
0.078
AC 10
0.9
0.2
We note that alternative 1, i.e. in-house manufacturing, is relatively more expensive that others alternative. This is due mainly to supply costs because in our hypothesis we consider that the raw material provider is localized in china.
in order to assess local performance for each site, technical and economical objective and risk objective will be considered with the same importance : and Importance related to the site of production: Table 5 Importance of production site
site 1
site 2
site 3
site 4
site 5
0,2
0,2
0,2
0,2
0,2
All site locations are assumed to have the same importance. strategy of compensation : Compensation will be considered between technoeconomical objectives. We set the trade-off strategy parameter s=100 In order to evaluate the local performance for each site, compensation will not be considered between TCO and risk objective. We set the trade-off strategy parameter s=-100 In order to evaluate the local performance for each site, compensation will not be considered between TCO and risk objective. We set the trade-off strategy parameter s=-100
saitsfaction value of the objective cost
1/3
Socio-economical objective
Table 6 : cost obtained for each alternative
0,90 0,80 0,70 0,60 0,50 0,40 0,30 0,20
Alternative 1 Alternative 2 Alternative 3 site 1
site 2
site 3
site 4
site 5
Figure 8 :Evolution of the cost satisfaction value
VII.3.2. evaluation of technical capability objective: Technical capability is evaluated for both externalization and internalization alternatives. The manufacturing activity of the considered component doesn't require an important technical knowhow. Externalization alternatives may provide better satisfaction than in-house manufacturing. Mainly because internal alternative is strongly dependent on system mobility and availability of local qualified operators.
Satisfaction value
Tech. capability
Technical capability
VII.3.1. Cost objective evaluation : For each site, we evaluate the cost induced by each alternative, costs are expressed in unit cost :
0,6 0,5 0,4 0,3 0,2 0,1 0
alternative 1 alternative 2 alternative 3
site 1 site 2 site 3 site 4 site 5 Figure 9 : Satisfaction value of the technical capability objective
VII.3.3. evaluation of socio-economical objective:
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Satisfaction value
Impact of each alternative on local employment creation is assessed. Thanks to system mobility, internal alternative may have positive impact on the local social and economical environment. Satisfaction of the socio-economical objective is directly related to production location. Results show that alternative 1 presents overall satisfaction, alternative 2 is satisfactory for site 1 as the provider plant is localized in the same country than site 1. Alternative 3 doesn't satisfy socioeconomical objective. 1 0,8 0,6 0,4 0,2 0
alternative 1
VII.3.6. Local performance Evaluation: Non compensatory aggregation is made between technicaleconomical objective (TCO) and risk objective in order to enable assessment of local performance for each alternative, and that for each site location. Figure 13 shows alternative 1 ranked 1. 1 0,8
alternative 1
0,6
alternative 2 alternative 3
0,4 site 1 site 2 site 3 site 4 site 5 Figure 13 : Local Performance Evaluation
alternative 2 alternative 3 site 1 site 2 site 3 site 4 site 5 Figure 10 :Satisfaction of the socio-economical objective
VII.3.4. evaluation of technical and economical objective (TCO): Technical and economical objective is assessed from cost, technical capability and socio-economical objectives. Compensation is considered between these attributes. For alternative 1, poor satisfaction values of cost and technical objectives are compensated by the satisfaction of the socioeconomical objective.
VII.3.7. Global performance Evaluation: The global make or buy decision must be made by accounting for all local performance evaluations. Compensation is made between different sites. This implies that business 'strategic plan included that sites with negative financial results can be compensated by other sites with 1 alternative 1 0,9 alternative 2 0,8 alternative 3
Satisfaction value
0,7 GPE Figure 14 : Global performance evaluation
1 0,9 0,8 0,7 0,6 0,5
alternative 1 alternative 2 alternative 3
site 1 site 2 site 3 site 4 site 5 Figure 11 : evaluation of Technical and economical objective
VII.3.5. evaluation of risk objective: Alternative 1 allows better control of risk factors, because in this case technology diffusion risk doesn't exist, supply disruption and product degradation risks are reduced because supplying raw materials has less value than supplying finite components. In the other hand, internal risks are more important in the case of internalization because more resources are needed, in consequent, human and machinery failures have more impact in this case. 1,00 0,80
alternative 1
0,60
alternative 2 alternative 3
0,40 site 1
site 2 site 3 site 4 site 5 Figure 12 : Risk Objective
positive results. Figure 14 shows that alternative 1 presents in this case the best solution regarding the 5 sites. CONCLUSION AND OUTLOOK The paper aims to propose a structured decision model adapted for reconfigurable systems in multi-site context. Although the financial objective has traditionally dominated the analysis of make or buy alternatives, this research demonstrates that is possible to consider strategic and technological issues in connection with the decision. The study allows to consider specific characteristics of the reconfigurable manufacturing systems and provides a model that take into account a longer term vision. There are additional areas to investigate. We considered that all providers and production sites were well identified. However, it depends on the commercial strategy of the firm. uncertainty about future clients and likely suppliers should be considered. References Collignan, Arnaud. 2011. “Méthode D’optimisation et D’aide À La Décision En Conception Mécanique: Application À Une Structure Aéronautique”. Université Sciences et Technologies-Bordeaux I. http://hal.archivesouvertes.fr/tel-00662303/. Faris, Charles W., Yoram Wind, Marketing Science Institute, and Patrick J. Robinson. 1967. Industrial Buying and Creative Marketing. Boston: Allyn & Bacon.
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