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This article was downloaded by: [University of Sunderland] On: 29 December 2014, At: 19:31 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Production Planning & Control: The Management of Operations Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tppc20 A multi-dimensional classification of production systems for the design and selection of production planning and control systems Bart L. Maccarthy a & Flavio C. F. Fernandes b a Division of Maufacturing Engineering and Operations Management , University of Nottingham , University Park b Department of Production Engineering , Federal University of Sao Carlos , via Washington Luiz, KM 235-13565-905, Sao Carlos, SP, Brazil Published online: 15 Nov 2010. To cite this article: Bart L. Maccarthy & Flavio C. F. Fernandes (2000) A multi-dimensional classification of production systems for the design and selection of production planning and control systems, Production Planning & Control: The Management of Operations, 11:5, 481-496, DOI: 10.1080/09537280050051988 To link to this article: http://dx.doi.org/10.1080/09537280050051988 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. 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Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions http://www.tandfonline.com/loi/tppc20 http://www.tandfonline.com/action/showCitFormats?doi=10.1080/09537280050051988 http://dx.doi.org/10.1080/09537280050051988 http://www.tandfonline.com/page/terms-and-conditions PRODUCTION PLANNING & CONTROL, 2000, VOL. 11, NO. 5, 481 ± 496 A multi-dimensional classi® cation of production systems for the design and selection of production planning and control systems BART L. MACCARTHY and FLAVIO C. F. FERNANDES Keywords production systems, classi® cation, production planning and control, analysis and design of production systems Abstract. A primary requirement for improved understanding of the management of production systems is an appropriate classi® cation of such systems. This paper proposes a classi® ca- tion that facilitates a better understanding of real production systems. It combines all the essential features, e.g. the ¯ ow of materials with new classi® cation perspectives with respect to response time, repetitiveness and work organization. As much previous work has in¯ uenced the approach proposed here, the paper also presents a review of relevant literature. The classi® - cation has four groups of characteristics, comprising eight dimensions of descriptors, encompassing 12 variables. Choosing or designing an appropriate production planning and control system (PPCS) is a di� cult task due to the integrative character of the production planning and control area: it tends to inter- face with all functional areas of the enterprise. An important objective of the classi® cation system proposed here is to provide a tool to assist in undertaking this di� cult task. Real production systems are becoming more hybrid in order to be able to cope with change. We show that our classi® cation can successfully deal with such systems. 1. Introduction Scienti® c knowledge is based on classi® cation. It has been asserted for instance that expert systems are, in gen- eral, classi® cation systems (Jain 1988) . It is not surprising therefore that a classi® cation of classi® cations has been given. Good (1965) proposed the following classes based Authors: B. L. MacCarthy, Division of Maufacturing Engineering and Operations Management, University of Nottingham, University Park, Nottingham NG7 2RD, UK, and F. C. F. Fernandes, Department of Production Engineering at Federal University of SaÄ o Carlos, via Washington Luiz, KM 235-13565-905 , SaÄ o Carlos, SP, Brazil. BART MACCARTHY is a Senior Lecturer in the Division of Manufacturing Engineering and Operations Management at the University of Nottingham. Prior to his appointment in 1987 he had substantial experience in research and management in manufacturing industry including the engineering, textiles and clothing sectors. He has been Vice-Dean of the Faculty of Engineering for 3 years and was acting Head of Division during the academic year 1996/1997. His research spans systems analysis, modelling, optimization, and simulation in manufacturing, operations and logis- tics. He has researched and published widely on decision support for planning and scheduling. Current research projects include the analysis and modelling of responsiveness in order ful® llment processes, statistical process control for performance measurement in scheduling and the modelling of supply chains in the public sector. FLAVIO C. F. FERNANDES has been an Assistant Professor at the Federal University of SaÄ o Carlos in Brazil since 1991. He has authored more than 30 papers on production planning and control and operations research, and refereed for several academic and professional journals. During 1988 he has been a visiting scholar in the Division of Manufacturing Engineering and Operations Management of the University of Nottingham in the UK. One of his principal current interests is how to reduce the gap between theory and practice in the production planning and control ® eld. Production Planning & Control ISSN 0953± 7287 print/ISSN 1366± 5871 online # 2000 Taylor & Francis Ltd http://www.tandf.co.uk/journals D ow nl oa de d by [ U ni ve rs ity o f Su nd er la nd ] at 1 9: 31 2 9 D ec em be r 20 14 on the purposes of producing classi® cations: ( i) for men- tal clari® cation and communication; ( ii) for discovering new ® elds for research; ( iii) for planning an organiza- tional structure or machine; ( iv) as a check list; (v) for fun. The classi® cation we propose in this paper falls prin- cipally into the third group but, as our classi® cation argues a new point of view, it is also useful for mental clari® cation and communication. Burbidge (1985) noted that when an engineer designs a machine, laws of physics and metallurgy help to produce an e� cient design, but there is not a set of scienti® c laws to help a production engineer faced with the problem of designing an e� cient production system. We contend that this situation has not changed signi® cantly in the intervening years. One of the reasons for this is that there is not an appropriate classi® cation of real produc- tion systems. Existing classi® cations are oversimpli ® ed, only consider a limited number of aspects or take a spe- ci® c perspective. These classi® cations tend to be of little or limited value for analysing complex real production systems or for aiding operations managers in selecting or designing appropriate production planning and control systems (PPCSs) . Selecting or designing an appropriate PPCS isa di� cult task due to the integrative character of the production planning and control function: it tends to interface with all functional areas of the enterprise. A key aspect of designing or selecting an e� ective PPCS is the ability to classify production systems. This paper focuses on this area, as we believe it constitutes a signi® cant gap between theory and practice in operations management. It would be pretentious to propose a totally watertight classi® cation. Moreover, any such claim is likely to be easily contradictable. In practice any classi® cation is a trade-o� between the level of detail needed for usefulness and the level of aggregation desirable for usability. We believe our classi® cation here will be a signi® cant con- tribution for understanding complex real production systems, and for aiding design or selection of production planning and control systems in practice. This paper has been in¯ uenced by much previous work. Therefore, a literature survey is presented in sec- tion 2. The multi-dimensional classi® cation is presented in section 3. Section 4 shows how to apply the approach. The ® nal section presents the conclusions. 2. Review of literature on the classi� cation of production systems Here we survey the most important literature directly relevant to the aim of this paper. We have selected refer- ences that are illustrative of approaches taken to the subject. We present a review of classi® cations of produc- tion systems in section 2.1 and a fairly brief review of classi® cations of production subsystems in 2.2. In section 2.3 we highlight the limitations of existing classi® cations, especially from the perspective of PPCS. In particular we outline the major de® ciencies that need to be addressed with respect to contemporary manufacturing enterprises in section 2.4. 2.1. A review of production system classi�cation 2.1.1. Pioneering classi�cations The pioneering classi® cations are well known. Mallick and Gaudreau (1951) identi® ed three types of produc- tion: ( i) continuous process (with disintegration, e.g. petrol re® ning; or with integration, e.g. synthetic rubber processing) ; ( ii) mass production; and (iii) intermittent process. Wild (1971) splits the last type, names some of the classes di� erently and presents the following similar classi® cation: ( i) process manufacture; ( ii) mass produc- tion; ( iii) batch production; ( iv) jobbing manufacture (unitary production) . Many textbooks have followed this type of scheme. Burbidge (1962) de® ned the following production types: ( i) line production [batch quantity (BQ) : 1; type of ¯ ow (TF) : line] ; ( ii) batch production (BQ: more than 1; TF: functional) ; ( iii) jobbing production (BQ: same as order quantity, generally small; TF: functional) ; ( iv) pro- cess batch production (BQ: more than 1; TF: line) ; (v) process jobbing production (BQ: same as order quantity, generally small; TF: line) . The following types of layout were presented : ( i) functional layout; ( ii) group layout; and (iii) line layout. Burbidge (1971) , relating these types of layout and some characteristics of production control, de® nes seven types of production systems: ( i) line produc- tion; ( iii) line batch production; ( iii) group batch produc- tion; ( iv) functional batch production; (v) line jobbing production; (vi) group jobbing production; (vii) func- tional jobbing production. Insu� cient attention has been given to empirical data on real production systems. Woodward (1965, 1980) con- ducted research on manufacturing ® rms in a region in the UK. From information collected from 92 ® rms their pro- duction systems were then classi® ed into 11 categories: ( i) production of units to requirements; ( ii) production of prototypes ; ( iii) fabrication of large equipment in stages; ( iv) production of small batches to customers’ orders; (v) production of large batches; (vi) production of customers’ large batches on assembly lines; (vii) mass production; (viii) intermittent production of chemicals in multi-pur- pose plant; ( ix) continuous ¯ ow production of liquids, gases and crystalline substances ; (x) production of stan- dardized components in large batches subsequently assembled diversely; (xi) process production of crystalline 482 B. L. MacCarthy and F. C. F. Fernandes D ow nl oa de d by [ U ni ve rs ity o f Su nd er la nd ] at 1 9: 31 2 9 D ec em be r 20 14 substances, subsequently prepared for sale by standard- ized production methods. Eight ® rms did not ® t any of the categories, a further four were extremely mixed and the other two were in transition. The classi® cation of Conway et al. (1967) should also be noted as it is used particularly in operational research: ( i) single machine; ( ii) parallel machines; ( iii) ¯ ow-shop; and (iv) job-shop. As noted by Botta et al. (1997) , this was expanded by Lenstra to include hybrid organizations characterized by parallel machines at any processing stage. 2.1.2. Classi� cations derived by attributes Here we consider classi® cations based on attributes that are perceived as important in production systems or manufacturing enterprises more generally. Johnson and Montgomery (1974) classify production systems based on the types of products and processes as follows. ( i) Continuous system: few families of similar products produced on a large scale. ( ii) Intermittent system: fre- quent changes in the production stages from one product to another, as a consequence of the large variety of man- ufactured items. They identify two subclasses: (a) inter- mittent ¯ ow-shop system: the ¯ ow pattern of all items is the same; (b) intermittent job-shop system: items do not have the same ¯ ow pattern. ( iii) Large project system: products are complex and special, and in many cases, are produced in unitary quantities. They also consider a fourth typeÐ ( iv) the pure stock systemÐ where items are bought, warehoused, distributed and sold, without a processing phase. Observing that cellular manufacturing is intermediate in terms of application between the job-shop and the ¯ ow-shop, Black (1983) proposed the following classi® ca- tion: ( i) large project system; ( ii) job-shop; ( iii) cellular manufacturing; ( iv) ¯ ow-shop; (v) continuous system. Putnam (1983) summarized the basic di� erences between job-shop and ¯ ow-shop systems. Constable and New (1976) consider three characteris- tics in their approach: the structure of products (simple or complex) ; the layout ( in line, functional or group lay- out) ; and the nature of the customers’ orders ( for stock or by order) . Bu� a and Miller (1979) adopt a classi® cation with four types of inventory production systems: ( i) con- tinuous system for stock; ( ii) continuous system by order; ( iii) intermittent system for stock; and (iv) intermittent system by order. An intermittent system indicates that production occurs in lots. Large projects are included in category (iv) . Nys (1984) de® ned the technological system (TS) as the part of a manufacturing system that comprises a set of equipment for executing the technological process, the equipment being linked by a material ¯ ow and an infor- mation ¯ ow. He presented two equivalent classi® cations on the basis of features of useÐ a parallel classi® cation and a morphological block classi® cation. Schmidt et al. (1985) proposed classes derived from the relationship between task divisibility, routing restrictions and production rate uniformity. Frizelle (1989) presents a categorization for plants by means of three letters (V, A and T) that resemble the s̀hape’ of the plant. The `V plant’ ìs characterized by few raw materials subdividing into many ® nished products’ . The `A plant’ presents `many raw materials being assembled into few ® nished products’ . The `T plant’ has a number of components that `can be assembled in a multiplicity of ways’ . Sipper and Shapira (1989) classify production systems in accordance with the inventory control policy as: ( i)pure WIP system; ( ii) modi® ed WIP system (planned to partly satisfy expected shortages) ; ( iii) modi® ed JIT system (without any intermediate bu� er stock and lots greater than one) ; and (iv) pure JIT system (unitary lots) . In order to clarify the meaning of repetitive and inter- mittent manufacturing, De Toni and Panizzolo (1992) de® ne six categories of manufacturing systems: ( i) indi- vidual [type of plant (TP) : yards] ; ( ii) unique (TP: laboratories) ; ( iii) intermittent (TP: job-shops and cells) ; ( iv) discontinuous (TP: batch plants) ; (v) repeti- tive (TP: discrete lines) ; and (vi) continuous (TP: process lines) . The classes were obtained by combining classi® ca- tion of manufacturing systems, production volume and how the product is produced. Wild (1995) in his well-known textbook ® rst classi® es the operational system by function (manufacture, trans- port, supply and service) , and then by structure. Wild classi® es manufacturing systems as: ( i) make from stock, to stock, to customer; ( ii) make from source, to stock, to customer; ( iii) make from stock, direct to customer; ( iv) make from source, direct to customer. Pyoun et al. (1995) present a classi® cation of the realiz- able ¯ exibility in automated manufacturing systems. They identify: ( i) mass production; ( ii) mid-variety and mid-volume; and (iii) multi-variety and small-volume production systems. Jichao (1996) classi® es production systems for the purpose of variability detection, as: ( i) simple production system (includes either a single process or independent multiple processes) ; and (ii) complex pro- duction system (many processes with close inter-relation- ships) . Dulmet et al. (1997) propose a classi® cation of processes according to the relationship between process and product. In their approach the degree zero object is the product, degree one object has direct leverage on the product (e.g. tools and pallets) up to the degree n object, which has direct leverage on the degree n ¡ 1 object. They Multi-dimensional classi�cation of production systems 483 D ow nl oa de d by [ U ni ve rs ity o f Su nd er la nd ] at 1 9: 31 2 9 D ec em be r 20 14 state that it is su� cient to de�ne � ve levels for a description of a given shop. 2.1.3. Descriptive classi�cations These are classi® cations based on a description of the attributes of ® rms or production systems in a ® nite num- ber of classes. Ingham (1971) de® ned eight types of busi- ness according to the relationships between marketing and production. From his work, it is possible to identify the following classi® cation: make to stock; customize to order, i.e. the client can specify its needs in terms of design of certain class of products; make to order, i.e. the items among a wide range of options are manufac- tured after the con® rmation of customers’ orders; make to order and to stock, i.e. make from orders for a wide range of products and make for stock in the case of standard products with considerable and continual demand; make products to order and major components to stock (this class corresponds to what is now known as assemble to order) ; totally customized to order, i.e. t̀he ® rm does not o� er a range of products but a production service within the limits of its equipment’ . Barber and Hollier (1986a, 1986b) developed a classi- ® cation of engineering batch manufacturing companies based on questionnaire evidence. They propose six groups according to the level of production control com- plexity. It is clear that several of the measures have been di� cult to estimate or interpret for many ® rms and responses were necessarily subjective. McCarthy et al. (1997) consider the evolution of manu- facturing changes in order to show how to construct a classi® cation based on cladistics (Kitching et al. 1998) and give an example using the automotive sector. They emphasize that with cladistics ìt is possible to examine the way in which characters change within groups over time, the direction in which characters change, and the relative frequency with which they change . . . Thus, organizational cladograms can be used as a tool for achieving successful organizational change’ . Un- fortunately, other sectors are not nearly as well documen- ted in the literature as the automotive sector. 2.2. Classi�cations of production subsystems Important contributions were made by Petrov (1966) , Wild (1972) and Carrie (1975) . Aneke and Carrie (1984) integrated existing classi® cations of simple ¯ ow lines (mass production) and group technology ¯ ow line using six criteria. The classi® cation reduces to: ( i) single-prod- uct single-machine system; ( ii) single-product multi- machine system; ( iii) mixed-product single-machine system; ( iv) multi-product single-machine system; (v) mixed-product sequential ¯ ow line I, where all the prod- ucts have the same sequence of operations and there is no necessity for machine resetting; (vi) multi-product sequential ¯ ow line where products have the same opera- tional sequence but they have to be produced separately in batches; (vii) mixed-product bypass ¯ ow line I where some products are not processed in all machines and equipment resetting is not necessary ; (viii) mixed-prod- uct bypass ¯ ow line II, where some products are not processed in all machines and equipment resetting is necessary; ( ix) multi-product backtracking ¯ ow line where equipment resetting occurs, production is in batches and the variation in operational sequences is due to omitted and/or backtracked operations and the product ¯ ow is bidirectional; and (x) multi-product multidirectional backtracking system where the products are batched, the operational sequences are so varied that ¯ ow is multidirectional , and therefore, line production is not feasible. Burbidge (1970) identi® ed four categories of group technology systems: ( i) single-machine system; ( ii) group layout system; (iii) total group layout system (group layout plus classi® cation and coding system, value analysis, variety reduction, standardization ) ; and (iv) line ¯ ow system, with characteristics between class ( iii) and mass production. Many classi® cations of ¯ exible manufacturing systems (FMS) have been presented, e.g. Groover (1980) , Kusiak (1985) , and Maimon and Nof (1986) . Browne et al. (1984) classi® ed FMSs as: ¯ exible machining cells, ¯ ex- ible machining systems, ¯ exible transfer lines and ¯ exible transfer multi-lines. Stecke and Browne (1985) added the descriptor t̀ype of material handling system’ to the pre- vious classi® cation, so the resulting classi® cation is based on the ¯ ow pattern of parts and more speci® cally on the routing ¯ exibility. MacCarthy and Liu (1993) and Liu and MacCarthy (1996) presented a classi® cation scheme for FMSs based on a consistent set of de® nitions. They distinguished between: ( i) a single ¯ exible machine (SFM) ; ( ii) a ¯ exible manufacturing cell (FMC) ; ( iii) a multi-machine ¯ exible manufacturing system (MMFMS) ; and (iv) a multi-cell ¯ exible manufacturing system (MCFMS) , and show the relationship between them. 2.3. General comments on existing classi�cations The only signi® cant previous paper that we have found that has reviewed production system classi® cations is that by McCarthy (1995) with 14 references. He noted that previous classi® cations, with the exception of Barber and Hollier (1986a) , were subjective and that cladistics pro- 484 B. L. MacCarthy and F. C. F. Fernandes D ow nl oa de d by [ U ni ve rs ity o f Su nd er la nd ] at 1 9: 31 2 9 D ec em be r 20 14 vided a way of making an objective classi® cation. We would argue however that all classi® cations are necess- arily subjective and that the important issue is not the subjectivity of the classi® cation but rather its usefulness. Classi® cation has to be subjective because it represents an author’ s perspective on production systems. Although Barber and Hollier (1986a) use a quantitativeapproach in arriving at their classi® cation scheme, it is also sub- jective because the number of groups, the characteristics the system may possess and the factors utilized to measure the characteristics are all chosen. Moreover, McCarthy et al. (1997) also present an essentially subjective classi® - cation, e.g. there are many subjective choices in the chosen clade. All attempts at classi® cation are necessarily approxi- mations and can always be criticized on this basis. Any classi® cation involves choosing between the level of detail and the level of aggregation. However, if the perspective and the rationale are clear then the bene® ts of a good classi® cation are many. Some of the classi® cations dis- cussed here are useful in providing insight and under- standing of production systems, and some have clearly demonstrated their usefulness in particular domains. We argue, however, that there is a real need for classi® - cations with de® ned objectives and areas of application. Unfortunately this is not the case in many of the classi® - cations above. 2.4. Developing a classi�cation for the design or selection of PPCS The need for improved classi® cations for the study, analysis, design and management of production systems in today’ s global economies is clear. For example, Banerjee (1997) shows evidence that ìn spite of many millions having been spent in manufacturing planning and control systems . . . no real solution to the need for greater responsiveness and ¯ exibility has been found’ . In the context of contemporary manufacturing organiza- tions, and in particular their control systems, the follow- ing are drawbacks that can be applied in some measure to the classi® cations discussed above. . Too general or very super® cial to be of use in any context. . Disregard of important concepts, e.g. ¯ ow pattern. . Consideration of ¯ ow-shop characteristics only within group technology cells. . Placing the concept of job-shop in the context of ¯ ow lines. . Failing to distinguish between assembly lines and production lines. . Consider assembly as a process related only to assembly lines, ignoring the fact that other types of installations may also carry out assembly opera- tions. Many further issues are crucial in contemporary manufacturing organizations and need to be addressed in e� ective classi® cations. In the past, changes in business needs occurred at low speeds and simple classi® cations of production systems were appropriate as a basis for designing a production system. In today’ s environments, in order to accommodate more rapid changes, manu- facturing systems have become more and more hybrid. There is a real need for a classi® cation that treats hybrid production systems in depth. A further issue is that of work organization . Previous classi® cations do not con- sider this issue but it is vital in contemporary organiza- tions. Response time and repetitiveness are also critical variables from a control viewpoint and an e� ective clas- si® cation must address them. It is not su� cient just to add a new variable to an existing classi® cation. The over- all scheme must be coherent in order to be applied e� ec- tively. The classi® cation we present in the remainder of this paper addresses these issues and most of the points noted above in a rational way. Our principal objective is to aid the design and selection of production planning and con- trol systems. The previous classi® cations that were most in¯ uential to us are: Wild (1971) , Burbidge (1971) , Ingham (1971) , Johnson and Montgomery (1974) , Constable and New (1976) , Black (1983) and Aneke and Carrie (1984) . 3. A multi-dimensional classi� cation for production systems 3.1. Overall structure A production system may be de® ned as a set of inter- related elements that are designed to act in a manner that generates ® nal products whose commercial value exceeds the costs of generating them. From the nature of these elements, two types of subsystem may be identi® ed: physical systems and managerial systems. In the ® rst the elements are physical entities (e.g. a machine) and in the second the elements are procedures that transform data into information in a decision process (e.g. an MRP system) . Naturally people design and operate both types of subsystem and can therefore be considered as elements of both. Here we propose a multi-dimensional classi® cation for production systems. We identify four main groups of characteristics, comprising eight dimensions (A/B/C/D/ Multi-dimensional classi�cation of production systems 485 D ow nl oa de d by [ U ni ve rs ity o f Su nd er la nd ] at 1 9: 31 2 9 D ec em be r 20 14 E/F/G/H). Where appropriate, important variables within some of the dimensions have also been identi® ed. The four groups and their associated dimensions are as follows. (1) General characterization: encompasses the follow- ing dimensions: enterprise size (A) ; response time (B) ; repetitiveness (C) ; and automation level (D) . (2) Product characterization: encompasses the prod- uct description (E) . (3) Processing characterization: encompasses the pro- cessing description (F). (4) Assembly characterization: encompasses the dimensions: types of assembly (G) and types of work organization (H) . The choice of these groups, dimensions and variables was determined by our principal objective, i.e. that the classi® cation be a valuable tool for designing or choosing a PPC system. Our selection is in¯ uenced by our indus- trial and academic experience in PPC. It is our view that the dimensions, variables and levels represent a su� cient set in terms of breadth, depth and level of detail to cap- ture the salient characteristics of most production systems from the perspective of production planning and control. In particular we have addressed the de® ciencies of exist- ing classi® cations with respect to the reality of contem- porary manufacturing organizations. The relevance of the scheme to production planning and control systems is discussed in section 4, and examples of applications are presented in section 4.2. In the following section we present a description of the scheme. We enlarge on the discussion where we feel it necessary to justify our selection of dimensions and vari- ables. We also emphasize some parts of the classi® cation because of their importance and novelty. In particular we present new insights in relation to the existing classi- ® cation literature on response time, repetitiveness level, ¯ ow of materials and types of work organization. The latter we have highlighted under assembly but in some cases it may also be necessary to consider it under pro- cessing characteristics. Table 1 illustrates the structure of the classi® cation scheme. We use the forward slash symbol …=† to separate the dimensions and the underscore symbol …¡† to sepa- rate the variables. Letters and numbers are used as short- hand notation for levels or categories of each within each dimension. 3.2. Dimensions and variables of the classi�cation system 3.2.1. General characterization 3.2.1.1. First dimension ( A) : enterprise size Several descriptors may de® ne the size of an enterprise: turnover, number of employees, market share, etc. For the purpose of analysing the PPCS, turnover or revenue are not good descriptors because either or both may be large if, e.g. raw materials are very expensive. The more relevant descriptor of enterprise size is the number of employees. By the number of employees, a ® rm in the UK is considered large if it has more than 250 employees ( in Brazil, more than 500) and it is considered medium sized if the number of employees is between 50 and 250 (between 100 and 500 in Brazil) . 3.2.1.2. Second dimension ( B) : response time Simply stating that a production system is make-to- stock or make-to-order , etc. is of little use from the point of view of designing modern production planning and control systems. Here we identify the dimension, response time,which speci® es how, strategically, an enterprise wants to attend to its customers’ needs. Figure 1 illustrates three important parameters of an industrial production system: supplier lead time (SL), production lead time (PL) and distribution lead time (DL). The ®̀ rst tier’ refers to the ® rst vendor in the supply chain. The response time (RT) of the production system is the sum of SL, PL and DL. E� ective manage- 486 B. L. MacCarthy and F. C. F. Fernandes Table 1. The multi-dimensional classi® cation system (MDCS). General characterization * Enterprise size * Response time * Repetitiveness level * Automation level Product characterization Product description * Product structure * Level of customization * Number of products Processing characterization Processing description * Types of bu� er * Type of layout * Types of ¯ ow Assembly characterization * Types of assembly * Types of work organization D ow nl oa de d by [ U ni ve rs ity o f Su nd er la nd ] at 1 9: 31 2 9 D ec em be r 20 14 ment of response time is central to the achievement of competitive advantage. In the extreme case where the enterprise maintains stocks of all purchased materials and all ® nal products, RT equals DL. Essentially response time is a policy decision in¯ uenced by techno- logical and operational constraints, marketing, and customers’ requirements and strategy. We identify the following values for the parameter B of the classi® cation: . B ˆ SL ‡ PL ‡ DL if the system produces by order; . B ˆ DLa (P%) if the system produces for stock and the service level is equal to P%; . B ˆ DLb (P%) if the system does not produce (only buys, stocks, sells and delivers items) and the service level is equal to P%; . B ˆ PL‡ DL if the system produces to order but maintains stocks of raw materials; . B ˆ SL ‡ DL if the system does not produce but it sells to order. 3.2.1.3. Third dimension ( C) : repetitiveness In the report by APICS (1982) , the term `repetitive- ness’ is associated with the production volume of discrete items: the larger the volume, the more repetitive the production system is considered to be. However, in an environment where the production volume is very low due to very large processing times, e.g. one item per month, and the system only produces this item, then, in spite of the low production volume, clearly the system must be considered to be repetitive. Repetitiveness must therefore be considered to be a function of more variables than just production volume. The approach we adopt is to ® rstly de® ne what we mean by a repetitive product and then de® ne what we mean by repetitiveness of a production system. We de® ne a product to be repetitive if it consumes a signi® cant percentage of the annual available time of the production unit (we specify at least 5%). We de® ne a production system to be repetitive if at least 75% of the items that it produces are repetitive ones. We de® ne a production system to be non-repetitive if at least 75% of the items are non-repetitive and to be semi-repetitive if at least 25% of the items are repetitive and at least 25% of the items are non-repetitive. Undoubtedly these cut-o� points are somewhat arbi- trary, but they do re¯ ect our experience of real produc- tion systems. Using these de® nitions we identify a range from maximum repetitiveness (the pure continuous system) to the minimum repetitiveness ( large-scale projects) . . C ˆ PC: pure continuous system, e.g. petroleum re® ning. . C ˆ SC: semi-continuous system, e.g. each pro- cessing unit is a pure continuous system and there are combinations of routes through processing units. In the process industries these are sometimes known as batch processing production systems. . C ˆ MP: mass production system. Almost all items are repetitive. . C ˆ RP: repetitive production system. At least 75% of the items are repetitive. In the case of the metal/ mechanical parts sector, a typical RP production system is the cellular manufacturing system with ¯ ow-shop pattern of ¯ ow. . C ˆ SR : semi-repetitive production system. There are a considerable number of both repetitive and non-repetitive items. In the case of the mechanical parts sector, a typical SR production system is the cellular manufacturing system with job-shop pat- tern of ¯ ow. . C ˆ NR : non-repetitive production system. The majority (at least 75%) of items are not repetitive. . C ˆ LP: large projects. 3.2.1.4. Fourth dimension ( D) : automation level The importance of the automation level for the control of production systems has been recognized for a long time. Bright (1958) demonstrated that the nature of the control has a close relationship with the levels of auto- mation. We di� erentiate the following states. . N. Normal automation comprises all types of mechanization where the human has a high degree of participation at the operational or execution level. Here we include classical ¯ ow-shop and job- shops, cellular manufacturing systems with ¯ ow- shop characteristics (CM1 ) ; cellular manufacturing systems with job-shop characteristics (CM2 ) . In CM1 the ¯ ow pattern is common and in CM2 the ¯ ow pattern is variable, allowing stages to be missed out and allowing counter-¯ ows ( ® gure 2) . . F. Flexible automation has, at the operational or execution level, computer control taking the main Multi-dimensional classi�cation of production systems 487 Figure 1. Response time (RT) of a production system. D ow nl oa de d by [ U ni ve rs ity o f Su nd er la nd ] at 1 9: 31 2 9 D ec em be r 20 14 role by means of technologies, e.g. local area net- works and computer numerical control, and will often be accomplished by some form of FMS tech- nology. Here we distinguish between ¯ ow-shop ¯ ex- ible manufacturing system (FMS1) and job-shop ¯ exible manufacturing system (FMS2) . . R. Rigid automation is the type found in transfer lines with highly specialized and dedicated auto- matic equipment. . M. Mixed automation occurs where the production system has processing units with di� erent automa- tion levels. For example it could be composed of a manufacturing cell with normal level of automation and a FMS (¯ exible automation) . 3.2.2. Product characterization 3.2.2.1. Fourth dimension ( E) : product description We identify three variables under the product descrip- tion. . Product structure : here we simply di� erentiate between: SL: denoting single-level products requiring no assembly; and ML: denoting multi-level products requiring ass- embly. . Level of customization: we distinguish between the following. (1) Customized products where the clients de® ne all the parameters of the product design. (2) Semi-customized products where the clients de® ne part of the product design. (3) `Mushroom’ customization. Mather (1998) describes this concept as delaying product dif- ferentiation as late as possible in the production system. There are a number of standard com- ponents or modules that are combined in a large number ofways in the ® nal stages of the production system with just a few additional operations. (4) Standard products: the clients do not interfere in the product design. . Number of products: we distinguish between: S: for a single product; and M: for multiple products. Thus, a product characterization of ML_2_M describes a production system with multiple products having multi-levels and at least some customer-de® ned product design parameters. The idea of a homogeneous product range is important when we come to applying the classi® cation. By this we mean that all products fall into the same product characterization. We have seven possible sets of homogeneous products (SL_1, SL_2, SL_4, ML_1, ML_2, ML_3, ML_4) . The case SL_3 (single level and `mushroom’ customization) is not poss- ible. 3.2.3. Processing characterization 3.2.3.1. Fif th dimension ( F) : processing description This important aspect of production systems is repre- sented by three variables. .Types of layout: for this variable we identify the following types of layout: P: product layout; F: functional layout or layout by process; G: group layout; FP: ® xed position layout : the resources (human, equipment) move and not the product. . Types of bu� er : for this variable we distinguish between the following types of bu� er: (1) bu� ers before the ® rst production stage; (2) intermediary bu� ers between production stages; (3) bu� ers after the last production stage. . Types of ¯ ow: the third variable de® nes the follow- ing types of ¯ ow: F1: single-stage , e.g. a machining centre ; F2: single-stage with identical machines in parallel ; F3: single-stage with non-identical machines in parallel ; F4: unidirectional multi-stage processing (e.g. a classical ¯ ow-shop system) ; F5: unidirectional multi-stage processing that allows stages to be skipped; F6 : unidirectional multi-stage processing with equal machines in parallel; 488 B. L. MacCarthy and F. C. F. Fernandes Figure 2. Typical material ¯ ow in the semi-repetitive cellular manufacturing …CM2†. D ow nl oa de d by [ U ni ve rs ity o f Su nd er la nd ] at 1 9: 31 2 9 D ec em be r 20 14 F7: unidirectional multi-stage processing with iden- tical machines in parallel but allowing stages to be skipped ; F8: unidirectional multi-stage processing with non- identical machines in parallel ; F9: unidirectional multi-stage processing with non- identical machines in parallel, allowing stages to be skipped ; F10: multi-directional multi-stage processing (e.g. a classical job-shop) ; F11: multi-directional multi-stage processing with identical machines in parallel ; F12: multi-directional multi-stage processing non- identical machines in parallel. Obviously F12 is the most complex type of ¯ ow and all previous types are particular cases of this one. A descrip- tion, e.g. G_1-3_F5 is a processing facility with group layout and bu� ers before the ® rst and after the last pro- duction stages with type of ¯ ow F5 (unidirectional multi- stage processing that allows stages to be skipped) . 3.2.4. Assembly characterization 3.2.4.1. Seventh dimension ( H) We distinguish between nine types of assembly. . A1: Mixing (e.g. chemical ingredients) . . A2: Assembly of a large engineering project (e.g. a large bridge) typically in a layout of ® xed position. . A3: Assembly of heavy products (e.g. a large tool- machine) in a layout of ® xed position. . A4: Assembly of light products (e.g. a medical equipment) in one workstation or in one of a set of parallel workstations. . A5: Paced assembly line where a conveyor never stops and the workers may move to perform their tasks. . A6: Paced assembly line where a conveyor stops for a number of units of time (cycle time) and the workers remain ® xed at their individual work- stations. . A7: Semi-paced assembly line where a conveyor always moves and the worker releases the product only when he ® nishes his tasks. . A8: Unpaced assembly line where a conveyor always moves and the worker simply attaches the product to the conveyor when he ® nishes his tasks. . A9: Unpaced assembly line where a transporter only moves when a worker activates it after ® nishing his tasks (e.g. an overhead travelling crane) . Multi-dimensional classi�cation of production systems 489 Figure 4. Uni-directional, multi-stage processing with identical parallel machines. Figure 3. Single-stage processing, the general case. Figure 5. Uni-directional, multi-stage processing with non- identical parallel machines. Figure 6. Multi-directional, multi-stage processing with non- identical parallel machines. D ow nl oa de d by [ U ni ve rs ity o f Su nd er la nd ] at 1 9: 31 2 9 D ec em be r 20 14 3.2.4.2. Eighth dimension ( J ) : type of organization of the work For this dimension we adopt a classi® cation of the organization of the work based on Johnson (1991) . Our classi® cation is the ® rst to encompass this aspect. Work organization may also be relevant to other types of pro- cesses, but from a production control perspective it has much greater impact in assembly operations. We distin- guish the following ® ve types. . (I ) Individual work: the number of workers is equal to the number of workstations. In the case of as- sembly lines, the criterion for allocating each task to a workstation is the balancing of the whole line. Two speci® c categories can be identi® ed. (Ia) Without rotation. Each worker is ® xed on a workstation. (Ib) With rotation. After each task has been allo- cated to a workstation, the ® rst set of workers of the ® rst matched set of workstations form the ® rst team and the second set of workers form the second team, etc. Workers in the same team may rotate their workstations. . (T) Team work. The workstations (or sublines) are pre-de® ned and each one is operated by a single team with several workers. The tasks carried out by each worker of the teams are decided by balanc- ing of the subline. Two speci® c cases can be identi- ® ed. (Ta) Every task is assigned to a speci® c work- station. (Tb) Just some tasks are assigned to a speci® c work- station. . (G) Self-managed work groups. As in the team work cases the workstations are ® rst de® ned and then the tasks to be performed by each workstation, but the group of workers of each workstation has autonomy to organize the work inside the group. 4. Appraisal and application of the multi- dimensional classi� cation system 4.1. Relationships between the dimensions in the classi�cation scheme Certain groups of characteristics occur quite com- monly in production systems. Here we illustrate some typical relationships between the general characteriza- tion dimensions we have identi® ed. For instance, the numbers of employees, level of automation and size of the production system tend to be correlated. The size of the production system is closely related to important fea- tures of the production system, e.g. the amount of capital that can be invested in a PPCS. Also in real production systems there is a correspondence between the volume of production per product and variety of products, size of the production system and level of repetitiveness of the production system. The relationship between volume of production Q and variety of products P is well known. For high Q and low P a product layout is appropriate, for medium Q and medium P a group layout is appropriate, and for low Q and high P a functional layout is appropriate. The repe- titiveness level essentially combines P and Q in one vari- able. This is illustrated in ® gure 7 relating repetitiveness level and automation level. Here we plot the typical level of repetitiveness against the level of automation for some important modern manufacturing systems. The level of repetitiveness increases from job-shop, to CM2, CM1 and ¯ ow-shop systems. Naturally FMS1 has greater repeti- tiveness than FMS2. Transfer lines have the greatest repe- titiveness level. What is uncertain is the position of lines I and II ; this depends very much on the technology and control system employed in the FMS. The response time, level of customization and the way we apply our classi® cation enables us to treat the rela- tionship between the production system and the custo- mers in a deeper way than in traditional textbook classi® cations, e.g. Ingham (1971) and Wild (1995) . The response time and the level of customization describe the relationship between the production system and the market, and it is important therefore that literature related to PPC systems speci® es this relationship. 490 B. L. MacCarthy and F. C. F. Fernandes Figure 7. The level of automation and the level of repetitiveness. D ow nl oa de d by [ U ni ve rs ity o f Su nd er la nd ] at 1 9: 31 2 9 D ec em be r 20 14 4.2. Using the classi�cation to choose the overall structure of a PPCS All the 12 variables considered in our multi-dimen- sional classi® cation have directimpact on the complexity of the production planning and control (PPC) activities. Table 2 indicates the typical impact of each variable on the complexity of PPC activities and the relationship between each variable and the level of repetitiveness. Repetitiveness is an important variable in our classi® ca- tion and we believe it to be the key variable for choosing the overall structure of the PPCS. Table 2 also indicates the relationship between the variables and the choice of a PPCS. The last line of table 2 is justi® ed by the following reasoning: for discrete items the more repetitive the pro- duction system is the more likely that the simplest of all PPCSÐ the kanbanÐ can be chosen; for intermediate situations period batch control (PBC; Burbidge 1996) is likely to be appropriate and for non-repetitive situations an MRP-based approach is likely to be necessary. Kanban and PBC due to their logic and procedures do not work well in non-repetitive situations. For some cases there is the possibility to choose OPT type systems. For large projects, PERT/CPM may be the most appropriate choice. While the level of repetitiveness has a strong impact on the choice of basic PPCS, the other variables have sig- ni® cant impact on the complexity of the detailed system to be de® ned. For example, MRP may be chosen as the basic system but the parametrization of the system depends on the complexity of the PC activities. These are related to the variables in table 2 and also the con- straints that are restricting the production system. 4.3. Applying the scheme Table 3 gives a complete view of the attributes of the multi-dimensional classi® cation scheme. If the production system is composed of one set of homogenous products and one processing unit and/or one assembly unit, the application of the multidimen- Multi-dimensional classi�cation of production systems 491 Table 2. The variables and the choice of a PPC system. Level of repetitiveness of production systems Pure Semi Mass Semi- Non- Large Other variables continuous continuous production Repetitive repetitive repetitive projects Enterprise size For all levels of repetitiveness, the larger the enterprise the greater the complexity of production planning and control (PPC) activities Response time DL(a7P%) DL(a7P%) DL(a7P%) DL(a7P%) PL‡ DL PL‡ DL or SL‡ PL‡ DL SL‡ PL‡ DL Automation level Rigid Rigid Rigid Normal or Normal or Normal or Normal ¯ exible ¯ exible ¯ exible Product structure For all level of repetitiveness, the PPC activities for multi-level products are much more complex than for single- level products Level of Standard Standard Standard Standard Mushroom Semi- Customized customization products or mushroom or mushroom or mushroom or semi- customized customized or customized Number of products For all levels of repetitiveness, the PPC activities for multi-products are much more complex than for single- product Types of layout Product Product Product Group Group Functional Fixed layout layout layout layout layout layout position Types of bu� er (i) and ( iii) (i) , ( ii) (i) , ( ii) (i) , ( ii) (i) , ( ii) (i) , ( ii) Without and ( iii) and ( iii) and ( iii) or ( i) or (ii) bu� ers Types of ¯ ow The complexity of PPC activities increases from (F1) in direction to (F12) Types of assembly (A1) or (A1) or (A5) or (A6) (A5) or (A6) (A7) or (A8) (A3) or (A4) (A2) disassembly disassembly or (A7) or or (A7) or or (A9) or or no no assembly no assembly no assembly assembly Types of work If there is assembly, the type of work organization has organization a direct impact on the way you will balance the work in the assembly Basic production A spread- A spread- Kanban Kanban or PBC or MRP PERT/ control system sheet to sheet to PBC OPT CPM possible to be control the schedule chosen rate of ¯ ow the work D ow nl oa de d by [ U ni ve rs ity o f Su nd er la nd ] at 1 9: 31 2 9 D ec em be r 20 14 sional classi® cation is straightforward. Otherwise, we must consider the following general approach ( ® gure 8) . We have to make the following explicit. (1) The number ni of products in each case i …n1 ˆ jSL_1j ; . . . ;n7 ˆ jML_4j ; where the modulus sym- bol indicates the number of elements in the set) . (2) If the level of automation is mixed (dimension B ˆ M) then we have to specify for each pro- cessing unit the level of automation (ALi ) and other descriptors (type of layout, type of bu� er and type of ¯ ow). (3) An assembly characterization (dimensions G and H) for each assembly unit …1 ; . . . ;n†. 492 B. L. MacCarthy and F. C. F. Fernandes Table 3. Summary of multi-dimension classi® cation system (MDCS) . General characterization Processing characterization (A) * Enterprise size (F) * Processing description (L) : large number of employees * Types of layout (M) : medium number of employees (S) : single workstation (S) : small number of employees (P) : product layout (B) * Response time (F) : functional layout (layout by process) …SL‡ PL ‡ DL† if the system produces by order (G) : group layout …DL…a ¡ P%†† if the system produces for stock and (FP) : layout of ® xed position the service level is equal to P% * Types of bu� er …DL…b ¡ P%†† if the system does not produce (only buy, (1) : bu� er before the ® rst production stage stock, deliver and sell items) and the services level is (2) : bu� ers between intermediary stages equal to P% (3) : bu� er after the last product stage …PL ‡ DL† if the system produces by order but maintains * Types of ¯ ow stocks of raw materials (F1) : mono-stage …SL‡ DL† the system does not produce and attends the (F2) : mono-stage with equal machines in parallel clients by order (F3) : mono-stage with unequal machines in parallel (C) * Repetitiveness level (F4) : uni-directional multi-stages …PC† ! pure continuous system (F5) : variable unidirectional multi-stages …SC† ! semi-continuous system (F6) : uni-directional multi-stages with equal …MP† ! mass production system machines in parallel …RP† ! repetitive production system (F7) : variable uni-directional multi-stages with …SR† ! semi-repetitive production system equal machines in parallel …NR† ! non-repetitive production system (F8) : uni-directional multi-stages with unequal …LP† ! large project machines in parallel (D) * Automation level (F9) : variable uni-directional multi-stages with (N) : normal automation unequal machines in parallel (F) : ¯ exible automation (F10) : multi-directional multi-stages (R) : rigid automation (F11) : multi-directional multi-stages with equal (M) : mix automation machines in parallel (F12) : multi-directional multi-stages with unequal machines in parallel Product characterization Assembly characterization (E) * Product description (G) * Types of assembly * Product structure (A1) : mixture of chemical ingredients (SL) : single-level products (A2) : assembly of a large project (ML) : multi-level products (A3) : assembly of heavy products in a layout of * Level of customization ® xed position (1) : customized products (A4) : assembly of light products in one or in (2) : semi-customized products parallel workstations (3) : mushroom (A5) : paced assembly line where the conveyor (4) : standard products never stops * Number of products (A6) : paced assembly line where the conveyor stops (S) : single-products for C (cycle time) units of time (M) : multi-products (A7) : semi-paced assembly line (A8) : unpaced assembly line I (A9) : unpaced assembly line II (H) * Types of work organization (I) : individual workers (T) : work teams (G) : work groups D ow nl oa de d by [ U ni ve rs ity o f Su nd er la nd ] at 1 9: 31 2 9 D ec em be r 20 14 (4) Depending on the complexity of the production system, we may need to show the relationship between the processing units and bu� ers. A direc- ted graph may be an appropriate approach. Here we ® rst present a concise illustrative example and then apply the approach to four examples from the literature. A production systemmanufactures machines utilized in the construction of roads. There are 2000 employees. There are processing units with ¯ exible levels of automa- tion and others with normal levels of automation. The system produces to order but maintains stocks of raw materials. It is a semi-repetitive production system. The products are complex, standard, multilevel ones. There are ® ve processing units. The ® rst one has a functional layout with bu� ers between the intermediate stages, before the ® rst and after the last stage, a normal level of automation and a multi-directional multi-stage ¯ ow pattern with non-identical machines in parallel. The sec- ond and third processing units are manufacturing cells with normal levels of automation. The second one has a bu� er before the ® rst stage and a uni-directional ¯ ow pattern with identical machines in parallel. The third one has a bu� er after the last stage and a unidirectional ¯ ow-shop ¯ ow pattern. The fourth and ® fth processing units are ¯ exible manufacturing systems with job-shop type ¯ ow patterns and bu� er after the last stage. There is one assembly unit of the unpaced type where the con- veyor always moves and the worker only attaches the product to the conveyor when he ® nishes his tasks with normal level of automation operated by work groups. Figure 9 shows the classi® cation for this production system and ® gure 10 uses a directed graph to show the relationship between the units and the bu� ers. We have also applied the approach to four production systems described in recent literature in production plan- ning and control. Obviously the amount of detail given in each source is limited and variable, and the results are necessarily incomplete, but it was felt to be an objective test of the applicability of the approach. Table 4 sum- marizes the major characteristics of each of the systems from the information provided in the source. Artiba (1994) gives more detail for the processing char- acteristicsÐ a production system composed of six pro- cessing units all with ¯ ow pattern (F4) and the transport of the materials between adjacent workstations is made through pipes. The relationships among the six units are shown in ® gure 11 [e.g. the products that pass processing unit 1 (PU1) follow through to PU4 or PU5]. Multi-dimensional classi�cation of production systems 493 Figure 8. The general approach to apply the multi-dimensional classi® cation. Figure 9. The classi® cation for the example problem. D ow nl oa de d by [ U ni ve rs ity o f Su nd er la nd ] at 1 9: 31 2 9 D ec em be r 20 14 5. Conclusions Di� erent classi® cations and taxonomies are necessary for di� erent purposes as di� erent perspectives on manu- facturing systems are important for di� erent aspects of analysis and design. However, many previous classi® ca- tions have limited application: some are not explicit about the purpose of the proposed classi® cation and/or are very super® cial whilst others disregard important ele- ments. The lack of useful classi® cations is one reason that we believe underlies the lack of progress in operations management generally and production planning and control in particular. The classi® cation scheme described here can be suc- cessfully applied to real production systems because it can treat in-depth the typical hybrid cases that arise in 494 B. L. MacCarthy and F. C. F. Fernandes Figure 10. The relationship between units and bu� ers. Figure 11. The relationships among the six units (based on Artiba 1994). Table 4. Application of the MDCS to some literature examples. References Characterization Variables [1] [2] [3] [4] General * Enterprise size * * * * * Response time * * * * * Repetitiveness level NR MP MP SC * Automation level F R R R Product Product description: * Product structure ML ML ML ML * Level of customization 1 3 4 3 * Number of products M M M M Processing Processing discription: * Types of layout F S P P * Types of bu� ers 2 1± 3 2 1± 3 * Types of ¯ ow F11 F1 F4 ** Assembly * Types of assembly A4 A4 A5 A1 * Types of organization of work Ð Ð Ð 1 Notes: A trace …¡† means that the descriptor considered does not apply ; an asterisk …¤† means that the information was omitted; and a double asterisk …¤¤† means that additional description will be provided on the information cannot be put into a simple table. References: [1] Anwar, M. F. and Nagi, R., 1998, Integrated scheduling of material handling and manufacturing activities for just-in-time production of complex assemblies. International J ournal of Production Research, 36, 653± 681. [2] Maimon, O. Z. and Braha, D., 1998, A genetic algorithm approach to scheduling PCBs on a single machine. International J ournal of Production Research, 36, 761± 784. [3] Dowlatshahi, S., 1996, An e� cient solution for determining location and size of bu� er stocks. Production Planning & Control, 7, 282± 291. [4] Artiba, A., 1994, A rule-based planning system for parallel multiproduct manufacturing lines. Production Planning & Control, 5, 349± 359. D ow nl oa de d by [ U ni ve rs ity o f Su nd er la nd ] at 1 9: 31 2 9 D ec em be r 20 14 practice. Each speci® c production system demands a speci® c, if not unique, production control system. For example, under the general heading of assembly lines, there are in reality, several di� erent types, each of which requires a di� erent production control system. 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