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Procedia CIRP 60 ( 2017 ) 344 – 349

27th CIRP Design 2017 Product Production Complexity Research: Developments and Opportunities

Günther Schuha, Stefan Rudolfa, Michael Riesenera, Christian Döllea, Sebastian Schloessera,*

aRWTH Aachen University, Laboratory for Machine Tools and Production Engineering (WZL), Steinbachstr. 19, 52074 Aachen, Germany * Corresponding author. Tel.: +49 241 80 28019; fax: +49 241 80 627568. E-mail address: [email protected]

Abstract

Using complexity management to address the product-production system has become a substantial competitive factor for companies. As the industry is facing various challenges, which are structured in the so called complexity radar, scientific research has been intensified. This paper analyzes the current state and opportunities in the research area of product-production complexity by evaluating a total of 372 publications. The associated evaluation methodology was developed by using statistical methods to allocate publications to the complexity radar’s objectives and effects. The identification of addressed areas as well as progress in complexity management research allows for a deduction of further research opportunities. Furthermore, interdependencies between currently pursued research areas are analyzed, targeting at the exploration of multi-objective research topics. The extensive literature review comprehensively reveals the current state of complexity management research as well as further research opportunities.

© 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (©http://creativecommons.org/licenses/by-nc-nd/4.0/ 2017 The Authors. Published by Elsevier B.V.). Peer-reviewPeer-review under under responsibility responsibility of the scientifiof the scientificc committee committee of the 27th ofCIRP the Design The27th 6th CIRPConference International Design Conference. Conference on Through-life Engineering Services (TESConf 2017).

Keywords: Complexity Research, Complexity Management, Literature Review, Product Production Complexity

1. Introduction commonality within their products to manage complexity effectively [3]. 1.1. Background 450 2000 2015 An increasing number of segments in combination 400 with shorter product lifecycles induce complexity to the environment in which manufacturing companies are ] 350 + 35% operating. Increasing complexity is furthermore indicated by [number] number an increasing number of product variants. Fig. 1 shows the [ 300 development of product lifetime and number of available - 40% German Product model series

product model series (e.g. Limousine, Coupé, SUV) within Product model series 250 automotive the automotive industry in Germany. OEMs In 2000, the average product lifetime was about 10 years with an average of 300 available product model series, 5678910 11 12 whereas until 2015 the product lifetime decreased to 6 years Product lifetime [years] with an average of 415 model series [1,2]. Due to the challenges accompanied with growing Fig. 1. Development of product lifetime and number of product variants complexity and variety, the significance of complexity [1,2] management increased simultaneously. Therefore, companies from various industries such as automotive or As the effects of product commonality also affect machinery and plant engineering strive to achieve production as well as the , complexity

2212-8271 © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 27th CIRP Design Conference doi: 10.1016/j.procir.2017.01.006 Gü nther Schuh et al. / Procedia CIRP 60 ( 2017 ) 344 – 349 345 management has to be considered holistically. Therefore, this holistic framework to describe the focus of a publication research paper analyzes complexity from a product and dealing with the management of complexity. For the analysis production as well as from an internal and external, conducted in this paper, every quadrant represents an ’s or supplier’s point of view [4,5,6], which present objective, which describes the general focus of a publication. the objectives of this paper. These objectives are derived The four objectives and corresponding dichotomy from the complexity radar (see Fig. 2), which was developed dimensions are defined as follows [4]. While Fig. 2 shows a within the Cluster of Excellence “Integrative Production clockwise enumeration, the introduction and subsequent for High-Wage Countries” [7] at RWTH Aachen discussion of the objectives is lead by distinction between University. The complexity radar is used as the framework mainly Economies of Scope related issues, mixed issues and mainly Economies of Scale related issues. for this paper as it considers both the product and production perspective from an inside and an outside point of view of a Main dimensions Explainability Flexibility of addressing at the point of sale the product architecture Economies of Scope company. By doing this complexity and its management is Product portfolio Product architecture examined holistically. The aim of this paper is to substantiate known facts I II the product architecture regarding complexity management as well as finding further variety of Fit research opportunities by aid of statistical analyses. In order Commonality of to enclose the focus of the present research paper, a short IV III definition for complexity is given as it is understood in this Process commonality performance chain Supply study [8,9]: Product and Production complexity is the variety Supply chain Production structure Main dimensions within a product or within production, depending on the Supply chain Resource addressing number of involved parts or process types and their efficiency utilisation Economies of Scale variability over time. Based on the given definition, this Fig. 2. The complexity radar is the paper’s framework [5] paper compiles publications focusing on complexity within the product-production system, which is induced by product Product portfolio complexity and product variety. The conducted analysis aims to identify areas of the product-production system which are The “Product portfolio” is the range of products as it is recognized from an external customer’s point of view. already explored in detail in terms of complexity Within this objective two opposing dimensions can be management. In addition to the focal areas, this paper shows identified. On the one hand, a product portfolio aims to the development of the significance of complexity supply diversified products which generate benefit for the management within the deducted areas. Therefore, this individual customer. On the other hand, a product portfolio approach helps to identify the main focus of past publications consisting of too many different products complicates the as well as possible future areas of research. As the oldest identification of the diversification as the customer is not analyzed publication was published in 1983, publications of able to choose the product fitting his needs. The first the last 33 years are taken into account to determine the dimension is described as the “fit of variety”, whereas the development of complexity management. In total, 372 second dimension is named “explainability at the point of publications are analyzed regarding their addressed sale”. objectives and effects. After presenting the underlying data-set for the statistical Product architecture analysis, the results of the evaluation are presented in the The “Product architecture” represents the internal context of the complexity radar in the second section. The objective of the product. The inner structure in terms of third section focuses on the derivation of opportunities for product architecture describes a product’s functions and further research in complexity management based on the components [11]. The effects aimed at within this field are findings of the analysis after which the fourth section “flexibility of the product architecture” and “commonality of summarizes the results and critically reflects on the given the product architecture”. Flexibility describes the ability to deductions. derive product variants in order to meet the demand of the market. Commonality defines the similarity between product 1.2. Scope of the “Product Production Complexity variants in terms of requirements, functions, or Research” product-parts. In combination with the first objective it describes the transformation of internal variety into external One major challenge for today’s product-production variety [12]. management is to resolve the dilemma between economies of scale and economies of scope [4,5,10]. This dilemma has Supply Chain been an objective to research for several years and is closely The objective “Supply chain” represents the external view connected to research regarding complexity and complexity onto production and focuses on the interface between the management. Therefore, the complexity radar (see Fig. 2) is supplier and the customer. The dimension “Supply chain introduced, which visualizes a close connection between the capital efficiency” describes the ratio between capital fixed dichotomy of scale, scope and complexity management. for the product range and the achieved sales. The dimension Due to the differentiation between product and production “Supply chain performance” is determined by the reliability as well as internal and external view, the radar makes up a of the supply chain. 346 Gü nther Schuh et al. / Procedia CIRP 60 ( 2017 ) 344 – 349

further terms per objective and effect were defined in order Production Structure to representatively analyze and evaluate the publications. The “Production structure” relates to the company’s 2.2. Development of complexity management within the resources and the way they are used within the production process. “Process commonality” and “resource utilisation” literature also describe a dichotomy as adaptions and variations, which As a first step of the analysis, the references were have to be avoided in order to reach a high utilisation, allocated to search terms continuing with an evaluation of represent the requirements for flexible processes in order to the number of namings of different terms identified by the reach process commonality. algorithm. The analyzed data set contains 372 publications. 83 publications (22%) are associated with “Product 2. Complexity management literature evaluation portfolio”, 142 publications (38%) are allocated to the radar field “Product architecture”, 127 publications (34%) belong

2.1. Corpus composition and literature evaluation to the objective “Supply chain” and 20 publications (5%) address the ”Production structure” (see Fig. 3). The data set construction was conducted in terms of a 142 127 corpus selection. A corpus is a “…subset of an ETL (38,17%) [Eletronic text library], built according to explicit design 83 (34,14%) (22,31%) criteria for a specific purpose” [13]. For the given analysis, 20 the corpus was derived from publications known at the (5,38%) Laboratory for Machine Tools and Production Engineering (WZL) of RWTH Aachen University due to the research Product Product Supply chain Production within the field of complexity and variety management and portfolio architecture structure

the ISI Web of Science (http://apps.webofknowledge.com). Fig. 3. Papers within different quadrants The criteria used for the corpus selection were derived from the four objectives of the complexity radar, combined with The distribution of the publications between the four “complexity” or “variety”. Within both sources a total of 372 objectives can be explained by the general focus of references were identified (the set of 372 publications, complexity management. Complexity management aims at representing the basis of the presented research is not both, mastering internal variety and offering a wide product specified in this bibliography). The evaluation of the portfolio of highly individualized products [15]. The internal publications was conducted by aid of an algorithm, which analysis of the product in terms of the objective “Product was provided by the Knowledge Exchange (KEX) AG, a architecture” makes up the interface between “Supply spin-off of the Laboratory for Machine Tools and Production chain”, “Production structure” and “Product portfolio” and Engineering (WZL) of RWTH Aachen University. The is often directly addressed by complexity management algorithm is able to conduct a full text search and distribute measures. The production structure is highly dependent on the number of namings of predefined terms. These the product architecture complexity. Therefore, it is often predefined terms in this case were derived from the indirectly addressed by complexity measures focussing the complexity radar’s objectives and effects as well as their product architecture explaining the rather limited number of synonyms. publications associated to “Production structure” [16]. This definition of terms requires knowledge about the Until now, the allocation of publications to the different investigated field of research in analogy to a white-box objectives has been conducted by aid of the search term the analysis, where the internal structure of a tested device is respective publication was found by. As the search term not known [14]. The disadvantage of such a white-box analysis always fully represents the focus of a publication, the is the risk, not to consider relevant terms, which could lead allocation to the quadrants of the complexity radar was to a biased analysis. In order to evaluate the focus of the adjusted by taking the results of the full text analysis different publications regarding the dimensions of the conducted by the algorithm into account. For the complexity radar, a white-box analysis was chosen despite reallocation, which makes up the basis for any further of the named disadvantage. As the algorithm applied to analysis, the focus of a publication on a specific objective analyze the publications can only present the absolute was determined by evaluating the amount of namings of number of findings of a certain term within a paper, the synonyms per page for an objective within the publication. results were scaled by dividing the absolute number of The allocation of a publication to a dimension of the namings by the number of pages. Therefore, the average complexity radar was afterwards conducted by comparing number of namings per page serves as an indicator for the which synonyms were most frequently used and which focus of a publication. objective they were assigned to. Fig. 4 shows the amount of In spite of the holistic description of product-production publications assigned to the different quadrants based upon complexity the derived objectives and effects of the this new allocation. The quadrants “Product portfolio” and complexity radar condense several terms. For instance, the “Product architecture” contain nearly the same amount of objective “Product portfolio” can be synonymously publications after the reallocation whereas the objective addressed by terms such as “Product family”, “Product line” “Supply chain” includes fewer references. The fact that the or “Product variety”. Analogous, the effect “Fit of variety” number of publications associated to “Production structure” is equally addressed by terms such as “Diversification” or doubles constitutes the importance of the production “Individualization”. As a result, up to 10 synonyms and structure in the context of complexity management. In Gü nther Schuh et al. / Procedia CIRP 60 ( 2017 ) 344 – 349 347 absolute numbers, the objective “Product architecture” “Variety and complexity within the product portfolio have contains the maximum number of publications. This finding to be reproduced and are therefore the root cause for supports the earlier statement and is underlined by the complexity within the product-production system.” following conclusion: Though the number of publications within the different “The product architecture is the main starting point for objectives already provides insight into the focus of research complexity management measures within the product- regarding complexity management, an analysis of the ” production system. development of the number of publications within the 138 142 (37,10%) Search term based allocation different objectives was performed. Fig. 6 illustrates the (38,17%) 127 Focus based allocation 104 results of the analysis over the considered period. 88 (34,14%) 83 (27,96%) (23,66%) 140 (22,31%) 42 PA: 138 20 (11,29%) 120 (5,38%) 100 SC: 104 PP: 88 Product Product Supply Production 80 portfolio architecture chain structure 60 Fig. 4. Focus based allocation of the analyzed publications 40 PS: 42

20 Beyond the absolute numbers of allocations, the trend of 0 reallocation in terms of original and target quadrant contains 1980 1985 1990 1995 2000 2005 2010 2015 information regarding the interdependency of the quadrants. PP = Product Portfolio PA = Product Architecture SC = Supply Chain PS = Production Structure The left side of Fig. 5 shows, which percentage of the Fig. 6. Development of the number of publications over the considered publications of a quadrant is reallocated to which other one period of time due to the maximum number of namings per page. In addition, the right side presents the composition of the “Strategic response to technological change in the quadrants after the focus based reallocation. It shows the electronic components industry” [17] is the oldest paper total number of publications after the reallocation in identified in the context of this research. The paper studies combination with the original objective. For instance, after product range variety due to the introduction of new the reallocation, the objective “Production structure” technologies and the resulting increase in complexity. In contains 42 publications, out of which 17 (40%) publications 1992, an increase of publications within the four objectives were initially allocated to “Production structure”, 8 (19%) was initiated. One year prior to that, Womack, Jones, & Roos publications were originally allocated to “Supply chain”, 9 published their book “The machine that changed the world” (21%) publications were originally allocated to “Product [18], which had a significant impact on the industry and architecture” and 8 (19%) publications were initially scientific community. The approach of Lean Thinking is allocated to “Product portfolio”. closely linked to complexity management as complexity is 145 Old allocation (search term based) likely to cause waste. Nevertheless, it mainly focuses on PS SC PP PA SC PS PA PS waste elimination within production, explaining why most of 57% 10% 9% 20% 105 the references dealt with complexity in the context of PP 86 production structure through the end of the last century. 16% 84% 5% PA 126 Since 1999 the objective product architecture contains the (87%) highest number of publications. The publications published 18% 69% 5% 88 42 SC 1% (84%) 8 in this year mainly deal with the possibility of product 9 26 8 modularization as a response to the challenges due to 10% 6% 6% 85% (30%) 17 New allocationNew (focus based) PS increasing market dynamics and shorter product lifecycles. PP PA SC PS In the context of this research, it is plausible that until now PP = Product Portfolio PA = Product Architecture SC = Supply Chain PS = Production Structure product architecture represents the objective with the most Fig. 5. Composition of the objectives due to the focus based allocation publications. Complexity in the focused context often Furthermore, Fig. 5 shows that publications initially addresses product complexity, as it affects the complexity assigned to the objective “Product portfolio” rather focus within the whole company and therefore offers great other objectives as a relatively high amount of publications potential for complexity management measures. Since 2005, is reallocated to different objectives (16% to “product especially the amount of publications associated with architecture”, 18% to “Supply chain”, 10% to “Production product architecture increased significantly which is mainly structure”) after the focus based allocation. This caused by the rising interest of companies in product development can be explained by the dependency of internal platforms and modularization. and external variety. External complexity and variety within the product portfolio directly affects the internal variety In conclusion, a total of 372 publications was allocated to the connected to the product architecture and production different objectives of the complexity radar by using an structure. In addition, the supply chain is affected as portfolio algorithm to evaluate the occurrence of initially defined variety demands a wider number of suppliers and search terms. As a result, the objective “Product distribution channels. Based on the prior observations the architechture“ was identified as the main starting point for following statement is derived: complexity management measures whereas the objective “Product portfolio” represents the root cause for complexity within the product-production system. 348 Gü nther Schuh et al. / Procedia CIRP 60 ( 2017 ) 344 – 349

2.3. Scope analysis of the literature For instance, 77% percent of the namings of effects regarding “Product architecture” within “Product portfolio” This section focuses on the analysis of interdependencies publications are associated to commonality of the product between the different objectives within the complexity radar. architecture. The observation that in most cases only one Fig. 7 shows the number of namings per page per paper of effect of a dilemma is addressed within the publications leads an objective by publications allocated to a quadrant (e.g. to the following conclusion: publications allocated to “Production structure” name terms “Current research focuses on optimising one objective describing “Production structure” 1.03 times per page). The rather than resolving the dichotomy by aid of complexity highest number of namings within each objective is obtained management measures.” by terms addressing the respective objective itself. The number of namings of the respective objective within 3. Opportunities in the context of complexity “Product architecture” and “Supply chain” is comparatively management high, whereas publications within the objective “Product portfolio” also address “Product architecture” and “Supply The increasing significance of complexity management chain”. This is caused by the variety, which is introduced regarding the product-production system is represented by the growing literature basis addressing this topic. A selected through the product portfolio and significantly impacts the corpus of the literature body was analyzed by aid of a full product architechture and supply chain. text analysis identifying pre-defined search terms within 4 3.5 these references. Bearing in mind possible deviations of the 3 analysis due to the chosen method, the following future areas 2.5 Publications allocated to production structure 2 averagely name terms associated with and further need for research are derived: production structure 1,03 times per page 1.5 1 Increasing the intensity of research within the different 0.5 quadrants 0 The references contained within the literature corpus to analyze areas of research regarding complexity management are not equally distributed throughout the four objectives.

PP = Product Portfolio PA = Product Architecture SC = Supply Chain PS = Production Structure Even after the focus based allocation, the amount of papers associated to the objective “Production structure” was low in Fig. 7. Dependencies between the objectives comparison to the other quantities. A holistic complexity management approach requires an equal and coordinated Besides the mentioned cross-references there has consideration of the quadrants of the complexity radar. obviously only been little research on a comprehensive view Therefore, it is necessary to intensify the research within the on the four main dimensions of complexity management. different quadrants to enhance resolving the dichotomies Taking the strong interrelation between Product portfolio, between the quadrants. Product architecture, Supply chain and Production structure into account, this fact is somewhat surprising and leads us to Intensifying interdisciplinary research the following statement: The development of an interdisciplinary approach is a key “Current research focuses on individual dimensions of necessity for holistic management. The identification of complexity management rather than comprehensively effects and interrelations helps conducting complexity looking at the four interrelated dimensions.” management more efficiently. A holistic understanding of the product-production system enables the employment of Complexity management aims at the reduction of the leveraging measures of complexity management rather than dilemmas visualized by the complexity radar. Therefore, addressing symptoms of product complexity and variety. publications addressing complexity management in a holistic Balancing the consideration of addressed effects and thus manner should focus on multiple effects within the focusing research effort objectives. Fig. 8 shows the distribution of the addressed effects within the four objectives of the complexity radar. The analysis revealed that the dimensions of the dichotomies were not addressed equally by the identified PP PA SC PS references. One major reason is the implicit consideration of Fit of variety 100% 100% 99% 98%

PP one dimension while addressing another. Explainablity at PoS 0% 0% 1% 2% Other explanations consider the unilateral contemplation of Flexibility of PA 23% 17% 53% 62% the dichotomy by addressing one effect and thus ignoring PA Comonality of PA 77% 83% 47% 38% relevant potential. Based upon the presented reasons for the

SC performance 87% 69% 90% 83% unilateral contemplation, future research can be focused to SC SC efficiency 13% 31% 10% 17% examine complexity in the context of the complexity radar. Process comonality 4% 45% 14% 31% Assessing the derived objectives and effects PS Resource utilisation 96% 55% 86% 69% The framework as well as the objectives and the effects of 96% of the namings regarding the production structure by publications allocated to product portfolio are associated to resource utilisation complexity management were derived from the complexity PP = Product Portfolio PA = Product Architecture SC = Supply Chain PS = Production Structure radar. Though this framework already considers complexity management in a holistic manner, it is necessary to critically Fig. 8. Effects addressed by the publications within different objectives assess considered objectives and effects in order to identify Gü nther Schuh et al. / Procedia CIRP 60 ( 2017 ) 344 – 349 349 further research areas. company specific ways to resolve the revealed dilemmas.

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