Jing Lin

Clotilde Rohleder
email: clotilde.rohleder@htwg-konstankz.de

Selmin Nurcan
email: nurcan@univ-paris1.fr

CHALLENGES OF INTEGRATING SOCIAL LIFECYCLE SUSTAINABILITY ASSESSMENT INTO PRODUCT LIFECYCLE MANAGEMENT -STATE OF THE ART

Keywords: Social Lifecycle Sustainability Assessment (S-LCSA), Product Lifecycle Management (PLM), structured literature review, Social-LCSA integration into PLM System, Social-LCSA Framework

Despite the importance of Social Life Cycle Sustainability Assessment (S-LCSA), little research has addressed its integration into Product Lifecycle Management (PLM) systems. This paper presents a structured review of relevant research and practice. Also, to address practical aspects in more detail, it focuses on challenges and potential for adoption of such an integrated system at an electronics company. We began by reviewing literature on implementations of Social-LCSA and identifying research needs. Then we investigated the status of Social-LCSA within the electronics industry, both by reviewing literature and interviewing decision makers, to identify challenges and the potential for adopting S-LCSA at an electronics company. We found low maturity of Social-LCSA, particularly difficulty in quantifying social sustainability. Adoption of Social-LCSA was less common among electronics industry suppliers, especially mining & smelting plants. Our results could provide a basis for conducting case studies that could further clarify issues involved in integrations of Social-LCSA into PLM systems.

Introduction

Increasingly pressure to improve sustainability comes from stakeholders such as society, non-profit-organizations (NPO), journalists, non-government-organizations (NGO), consumers and governments. Industries must respond, because production and products influence sustainability in at least three dimensions: economic, environmental and social. Industry must account for competition, changing markets that make the value chain a complex system, evolving laws and regulations. Manufacturing companies must undertake preventative approaches to environmental pollution within their manufacturing processes.

Consumers (C) and Government & Leadership (G) are playing increasingly active roles in achieving a sustainable world. Sustainability-driven manufacturing can provide a competitive advantage because it appeals to customers who value brand, image and reputation. Collaborative work increases the complexity of addressing sustainability. As shown in Fig. 1, Engineers & Designers (D), Manufacturer/Vendor (M) and Material Analyst (Ma), and other actors are involved in Sustainable World, cross-business functions. Globalization makes the situation more acute. A Life Cycle Assessment (LCA) tool can help determine impacts of products or systems over a range of environmental and resource issues. It measures all environmental impacts across the entire lifecycle. Currently, the most accepted framework and lifecycle-based approach for assessing a product's impacts on all three sustainability dimensions in an integrated way is Life Cycle Sustainability Assessment (LCSA). It is currently regarded as the only viable framework for comprehensive sustainability assessment of products. It can be understood as the evaluation of the combined positive and negative effects of a product over its entire lifecycle on the three dimensions of sustainability. 1 Life cycle sustainability assessment (LCSA) refers to the evaluation of all environmental, social and economic impacts in decision-making processes towards more sustainable products throughout their life cycles. This comprehensive assessment can be expressed by the following conceptual formula: where E-LCA denotes the conventional environmental lifecycle assessment, Social-LCA (Social Life Cycle Assessment) represents the assessment of positive and negative social impacts along the product life cycle. Experts disagree on whether LCC (Life Cycle Costing), the assessment of economic impacts along product lifecycle, is necessary for an analysis. However, if cash flow is important, include it in the analysis [START_REF] Tarne | Review of Life Cycle Sustainability Assessment and Potential for Its Adoption at an Automotive Company[END_REF].

[E-LCA] + [S-LCA] +[LCC] = [LCSA]
Early definitions of Life Cycle Management covered environmental, social and economic issues (Hunkeler et al. 2004;Remmen et al. 2007) along a product lifecycle. These ideas are in line with developments in life cycle assessment that further expand the context of LCA to include social and economic elements under the life cycle sustainability assessment (LCSA) framework (Finkbeiner et al. 2010;Klöpffer 2008; UNEP 2011). Some researchers identified new challenges related to the criticality of materials (Sonnemann et al. 2015). Incorporating LCSA in decision-making processes at the product, process and individual organizational levels could maximize profit. Finkbeiner (2011) was first to describe the term "lifecycle sustainability management (LCSM)." [START_REF] Sonnemann | Book "The LCA Compendium Book[END_REF].

Fig. 2 shows LCA defines a product system by the system boundary and the product lifecycle that is divided into stages for the inventory analysis (LCI). LCI considers the environmental inputs and outputs. At the broadest level four stages may be identified: material production, product manufacturing, product use, and product disposal.

In the lifecycle analysis of product systems, materials information is necessary wherever materials are used in manufacturing, in products, or needed as ancillary inputs. Hence, materials data are essential to an LCI and to a full LCA. Materials should be selected in each PLM stage to enable tracking and sustainability checks along PLM. Fig. 3 shows how we propose to align PLM with the material life cycle, since the product and materials cycles are parallel and intersecting. Some researchers have recommended enabling PLM for Material Selection because the potential of using PLM for material selection is great; e.g. Gabi… Knowledge about the environmental performance is important in the LCA design process. Fortunately, a lot of information is available in this process, especially in modern, powerful PDM/PLM tools. Linking LCA and PLM therefore can be a good start 3 , e.g. selecting recyclable materials, avoiding usage of fossil fuel, and tracking material flow from material extraction to final disposition.

Although the potential is great, little research has addressed how LCA can support PLM for Material Management. It is therefore worthwhile to discuss how LCA could be practiced to PLM in business contexts. For example, material selection is the prime concern of all engineering applications and design. This selection process can be defined by application requirements, possible materials, physical principles, and selection 4 . Selection of a material for engineering a new product involves several steps:

§ Decide the requirements of the application, in terms of mechanical, thermal, environmental, electrical and chemical properties. § Select materials for the application. This paper proposes to extend the definition of material properties to allow handling the conflict resource index (one of important social aspect) and sustainable properties that are remarked with a dotted line in Fig. 4. Furthermore, this paper aims also to organize the main references on Social-LCA to build a complete picture of the theoretical and practical implementation of this methodology in the electronics & electric sectors, especially with globalized supply chains. Also, it identifies needs for further research. The challenges and potential for Social-LCA at an electronic company will be identified to provide guidance for research into integrating Social-LCA with PLM and for managers attempting such integration. LCC is not covered in this paper because it is not essential to sustainability analysis in all situations. The research has the following structure: a. Literature review on Social-LCA with Integration into PLM to identify the main research needs. b. Identification of recent lifecycle-based product sustainability assessments of electronic companies having globalized supply chains. c. Findings about the challenges and potential of Social-LCA when integrated into PLM at an electronic company. These results could benefit decision-makers, stakeholders, enterprises and consumers.

Methods & Materials

Research approach

• Type of study (empirical, theoretical, or both).

• Research application areas (industry sector).

• Sustainability dimension (which of the three dimensions of LCA the publication addresses). • Type of case study (full case study or numerical example) • Data for case study (extent to which real data was collected) • Integration. Studies may be classified according to whether they address an integrated system, and if so, the kind of application of Social-LCA (Life Cycle Management (LCM); product lifecycle management (PLM), application life cycle management (ALM) for software, and data lifecycle management (DLM); information life cycle management (ILCM) [START_REF] Sonnemann | Book "The LCA Compendium Book[END_REF].

Evaluation of Current Status in the Electronics & Electric Industries

This part of the research was conducted independently of the structured literature review on Social-LCA. Our approach resembled that of John W. Sutherland et al. [16], who explored social impacts identified by national-level social indicators, frameworks and principles. We also examined methodology development and various challenges for social life cycle assessment. Martin Gerner found that "Quite a number of companies within the business segment are confronted with the dual challenge of both transforming their business models into future-proof concepts and paying tribute to an increase of sustainability awareness among customers simultaneously".

The gradual shift of business segments from hardware-related stationery and professional office supplies towards digitized media and IT business solutions addresses sustainability and corporate (social) responsibility as one core competence of related companies in a changing market environment (Altenburger, 2013; Stanger, 2017, p. 61; Zarnekow & Kolbe, 2013). It is reasonable to focus upon corporate sustainability or sustainable entrepreneurship (Schaltegger & Wagner, 2011, 225 et seqq.; Weidinger et al., 2014), interchangeably, examining subject plus contextual conditions. E.g. to analyze characters of industrial companies: are they "Innovation and business-model development" driven company, have a pivotal stake within the company's strategic development, e.g. heading for new product lines (eco-innovation), providing resourceful services, stretching brands etc.; or are they globally oriented companies, where cultural context plays important role.

Implications for Application at electronic & electric Company

In order to identify the most pressing challenges out of the ones identified by the two previous research steps to adopt Social-LCA, decision makers at electronic & electric company should be consulted. Interviews of experts and stakeholders should also reveal three types of knowledge for analysis: technical, procedural and interpretative. In reverse, an implementing concept will focus on the managerial aspects of corporate sustainability by returning analytically processed records to the case-presenting company [START_REF] Gerner | Assessing and managing sustainability in international perspective: corporate sustainability across cultures -towards a strategic framework implementation approach[END_REF].

Result & Decision

State of the Art of Social-LCA

The low amount of papers identified with our final keywords suggests that social Life Cycle Sustainability Assessment is still in an early stage of development. Our final set of 47 analyzed publications is consistent with the number of publications considered by other structured literature reviews [START_REF] Tarne | Review of Life Cycle Sustainability Assessment and Potential for Its Adoption at an Automotive Company[END_REF][START_REF] Gerner | Assessing and managing sustainability in international perspective: corporate sustainability across cultures -towards a strategic framework implementation approach[END_REF][START_REF]LCA Compendium-the complete World of Life Cycle Assessment (book series)[END_REF]. Table 2 shows the distribution of publications by source. All sources that contributed only one publication were subsumed under "Rest". It is easily to see that Springer is the main medium in field of social LCA with integration into Life Cycle management.

Bibliometric Results

Other important journals for LCA include The International Journal of life Cycle Assessment or Journal of cleaner Production, Journal of remanufacturing, etc. The type of study or focus of research is also important for the evaluation of publications. Fig. 6 shows that combined empirical and theoretical studies are mainly comprised of method developments that are subsequently tested by case study, which means the field of analyzed literature leans more strongly towards method development. Together with theoretical type of study, more than 90% of publications are about theorical and method development. This indicates also that the Social-LCA with integration into PLM is a new research area.

Table 3 show the distribution of publications by countries. Germany led (36%), followed by Italy (27%), Finland (11%), and USA (9%).

Classification of Literature by Thematic Fields

The maturity model was designed in such a way that a comprehensive capability analysis is possible in its application. It addresses the essential phases of the product life cycle: planning, development, production planning, production, and operational and service tasks. The BABOK [START_REF] Manda | Application of life cycle assessment for corporate sustainability: integrating environmental sustainability in business for value creation[END_REF] explains the key terms used here as follows.

Framework: A generic lifecycle analysis or lifecycle assessment (LCA) explains the system structure. Most research into LCA has focused on the principle logic and improvements of the analysis framework or on empirical tests of conceptual frameworks. Klöpffer [START_REF] Klöpffer | Is LCC relevant in a sustainability assessment? Springer published[END_REF] and Finkbeiner et al. [START_REF] Martínez-Blanco | Application challenges for the social Life Cycle Assessment of fertilizers within life cycle sustainability assessment[END_REF][START_REF] Nguyen | Adapting Ergonomic Assessments to Social Life Cycle Assessment[END_REF][START_REF] Finkbeiner | Life cycle sustainability assessment (LCSA) for products and processes[END_REF] defined the Life Cycle Sustainability Assessment framework. Martin Gerner (2019) [START_REF] Gerner | Assessing and managing sustainability in international perspective: corporate sustainability across cultures -towards a strategic framework implementation approach[END_REF] focused his research on LCA framework implementation strategy and applied the framework-implementation approach to corporate sustainability (Baumgartner & Rauter, 2017, pp. 82-83). He also reported examples of applications of LCA framework implementation and provided recommendations. See Fig. 7 & Fig. 8. Given a dual character of defining strategy by referring to both identifying and assessing present and future comparative advantages and potential for success and deriving detailed implications for policies and plans of implementation, the framework strategy explicitly focuses on conceptual guidelines for realizing such business opportunity (Morioka & de Carvalho, 2016; Rusnjak, 2014, p. 48-50).

PLM is mainly a business management concept for sustainable products that can be applied in the industrial and service sectors with the aim of improving specific goods and services and enhancing the overall sustainability performance of the business and its value chains. PLM appeals to businesses that are ambitious and are committed to reduce their environmental and socio-economic burden, while maximizing economic and social values. PLM is intended to create sustainable value rather than improve short-term success. So, PLM requires a holistic view and a full understanding of interdependency of businesses, environmental and social issues. [START_REF] Sonnemann | Part of the Springer Open Book LCA Compendium -The Complete World of Life Cycle Assessment book series (LCAC)[END_REF] Method & Method Integration: Publications about methods proposed extensions of or changes to higher-level frameworks. Research into method integration focused on case studies, applications of methods, or methodological triangulation.

Case-related research is mainly exploring, including interpreting-inductive elements grounded in contested assumptions and referring to underlying theoretic frameworks and methodological concepts of relevant importance (Gioia, Corley, & Hamilton, 2013, 17 et seqq.; Jastram, 2012, p. 53; Kromrey, 2002, 58 et seqq.). [START_REF] Gerner | Assessing and managing sustainability in international perspective: corporate sustainability across cultures -towards a strategic framework implementation approach[END_REF] Applications of methods addressed principles of qualitative content analysis (Atkinson, 2017, pp. 122-123; Mayring, 2014; Silverman, 2013, 340 et seqq.) to understand applications of theories on corporate sustainability. take into account the leading theoretical concepts applied by scholars on selected corporate contexts, and to identify how to adequately embed the intended case study; collecting case-related characteristics to elicit elucidating, confidential up-to-date information through a status-quo-analysis of sustainability-related strategic approaches, activities and initiatives, means and instruments, examine underlying corporate perceptions through SWOT-analysis, including business analysis (internal) and environment analysis (external), and to benchmark performance targets and monitoring processes through an analysis of potential or opportunity assessment, respectively; and processing obtained findings in a strategic-directional way to adopt the value-chain-oriented reasoning based upon an extended lifecycle assessment (Frostell, 2013, 842 et seqq.; Gauthier, 2005) as structuring element, apply a multimethod approach of methodological triangulation, relying on stakeholder observation, expert interviews and company resources, and frame case-related characteristics as case study, including data collection, data analysis and data evaluation [START_REF] Gerner | Assessing and managing sustainability in international perspective: corporate sustainability across cultures -towards a strategic framework implementation approach[END_REF].

Methodological triangulation improves research validity through combining various techniques. The blend of multiple methods, not to be confused with mixed method, ensures best possible use of different sources of information, and thus generating sound and methodologically-grounded results, pertaining to qualitative research models, in particular ( [START_REF] Manda | Application of life cycle assessment for corporate sustainability: integrating environmental sustainability in business for value creation[END_REF], Generally, this triangulation is evaluated by expert interviews, company resources and stakeholder observations. Alternative Assessment Methods: Most researchers developed unique assessment methods but some incorporated parts of LSCA or LCSA frameworks. Luthe et al. [START_REF] Luthe | A Systems Approach to Sustainable Technical Product Design[END_REF] developed a tool that integrates LCA, Social-LCA, and economical aspects into product design, while Mjörnell et al. [START_REF] Mjörnell | A Tool to Evaluate Different Renovation Alternatives with Regard to Sustainability[END_REF] integrated all three LCSA components into their sustainability assessment. Martin Gerner suggested integrating corporate sustainability into strategic management.

Case Studies: Most case studies tested applicability of the LCA framework and associated methods. Some case studies lacked effective ways of weighting sustainability dimensions and integrating all three dimensions. , there are also some case studies and improving data availability addressed by examined publications, especially for Social-LCA [START_REF] Gerner | Assessing and managing sustainability in international perspective: corporate sustainability across cultures -towards a strategic framework implementation approach[END_REF][START_REF] Martínez-Blanco | Application challenges for the social Life Cycle Assessment of fertilizers within life cycle sustainability assessment[END_REF], were additionally identified as potential areas for improvement. E.g. A case study using LCSA framework with special focus on Social-LCA on mineral and compost fertilizers was conducted by Martínez-Blanco et al. [START_REF] Martínez-Blanco | Application challenges for the social Life Cycle Assessment of fertilizers within life cycle sustainability assessment[END_REF] who used data from LCA databases (environmental impacts), LCC (purchase price), and Social-LCA to assess the sustainability impacts of fertilizers. Martin Gerner [START_REF] Gerner | Assessing and managing sustainability in international perspective: corporate sustainability across cultures -towards a strategic framework implementation approach[END_REF]

Current Status in the electronic & electric Industry

Most European electronic & electric companies that have integrated LCA into the product development process have not effectively integrated social and economic impact assessment. First steps towards the operationalization of Social LCA have been taken by co-founding the Roundtable for Product Social Metrics, an industry-led initiative that produced a handbook on implementing product social impact assessment.

[14] Environmental LCA is well-accepted and practiced throughout the world's top electric & electronics companies, like Siemens, Philips, GE, WAGO, BOSCH, etc., but few have employed comprehensive Life Cycle Sustainability Assessment of products. The immaturity of Social-LCA and the difficulty of gathering data on social impacts pose an additional barrier to implementing Social-LCA as part of an LCSA framework in industry. Most stake holders and experts consider an entire Social-LCA as too big a challenge, but many understand the importance of social risk assessment of supply chains in managing social risks.

There exists no universal strategy to integrate Social LCA into PLM (life Cycle Management). The strategy differs for each sub-cycle, including the following:

• Production management -Sustainability's focus is product stewardship, operational efficiency and/or innovative transformation • Packaging/distribution management -Sustainability's focus is operational efficiency and/or adaptive responsiveness • Service/use management -Sustainability's focus is product stewardship, innovative transformation and/or adaptive responsiveness • End-of-life management -Sustainability's focus is product stewardship and/or innovative transformation Industry is trending from corporate (social) responsibility towards an integrated concept of sustainability that is functionality-based and governance-oriented.

Implications for applications at electronic & electric Industry

Our research determined the state of the art in the field of Social LCA and highlighted major areas for future research. We reported the status of product sustainability assessment in the electronic & electric industry and implications for the next steps towards the operationalization of Social-LCA. We identified several challenges for operationalization that hinder the adoption of LCSA at electronic & electric company.

We propose the following guidelines for further research. Data collection: Accessing internal, often confidential company information requires close interplay between academic and corporate entities [START_REF] Gerner | Assessing and managing sustainability in international perspective: corporate sustainability across cultures -towards a strategic framework implementation approach[END_REF]. Researchers should prepare to handle different languages across a company. Questions should be formulated ad hoc referring to pre-structured questionnaires. Interviewers should follow common routine of salutation, reciprocal introduction, question and answer, brief discussion and feedback, follow-up, and leave-taking (Bogner et al., 2014, 27-48, 58 et seqq.; Gläser & Laudel, 2012, 83 et seqq.; Silverman, 2013, 199 et seqq.) [START_REF] Gerner | Assessing and managing sustainability in international perspective: corporate sustainability across cultures -towards a strategic framework implementation approach[END_REF]. Data analysis: In qualitative analysis, procedural arguments are to be granted priority over procedural arguments. Validity is of more importance than reliability. Data evaluation: Interpreting findings retrieving from qualitative data consequentially should follow the algorithms of qualitative content analysis Comparatively low maturity of Social-LCA -Ensure consistency of social topics with company specific strategy.

-Evaluate currently available databases and decide on a mode of data acquisition.

Limitations

We searched the literature using only three sources and narrowed down search terms to reduce the number of hits. Our narrow search focus may have overlooked some relevant publications, especially those that addressed only one method that could be a part of Social-LCA.

The research design included the social dimension in the lifecycle structure of analysis. Results of expert interviews, company resources and stakeholder observation revealed that assuming a generic, five-part lifecycle assessment represents a stylized or archetypal model of approaching corporate reality. Researchers must transfer or relate findings to the value-chain segments in the corporate structure. Without further research, our findings do not provide a basis for conclusions of a general nature. Our qualitative approach means findings pertain with certainty only to the cases studied [START_REF] Gerner | Assessing and managing sustainability in international perspective: corporate sustainability across cultures -towards a strategic framework implementation approach[END_REF].

Conclusion

This paper identified challenges and potential for implementing an integration of Social Life Cycle Assessment (Social-LCA) into Product lifecycle Management (PLM) at an electronic & electric company. The three-part structure sustainability performance, sustainability opportunity and sustainability commitment made it possible to first, assess the status quo of corporate sustainability-related strategic approaches, activities and initiatives, means and instruments; second, identify universal and culturebound drivers corresponding to industry-sector-specific characteristics; and third, deduce operational guidelines in view of stakeholder awareness, strategic options, projects and best practices [START_REF] Gerner | Assessing and managing sustainability in international perspective: corporate sustainability across cultures -towards a strategic framework implementation approach[END_REF].

Every sustainability dimension, i.e. environmental, societal, economic and cultural, should be studied individually and then correlated with the generic lifecycle category, i.e. supply chain, production, distribution/packaging, service/use, and end-of-life, and finally included into the afore mentioned three-step assessment.

Fig. 1 :

 1 Fig. 1: Actors in Sustainable World

Fig. 2 :Fig. 3 :

 23 Fig. 2: Using LCA approach for Material life cycle Fig. 3: PLM vs. Material Life Cycle

§

  Figure out what changes in the material properties are needed. § Pick materials, which best fulfil the requirements of the application given possible changes in the material properties.

Fig 4 :

 4 Fig 4: Extension of the Material Property DefinitionThis paper proposes to extend the definition of material properties to allow handling the conflict resource index (one of important social aspect) and sustainable properties that are remarked with a dotted line in Fig.4. Furthermore, this paper aims also to

2. 1 .

 1 Structured Literature Review of Social-LCA and PLM Integration We structured our literature review to yield reproducible results -a reliable knowledge base without research bias -using the following steps [3]: (I) Definition of review/check list; (II) Listing of research questions; (III) Identification of keywords; (IV) Selection of sources for literature search; (V) Define inclusion and exclusion criteria; (VI) Refining & finalizing keyword setting; (VII) Search of literature; (VIII) Evaluation and documentation of literature.

Fig. 5

 5 Fig. 5 shows the chronic development of research in field of Social-LCA (with integration into PLM). It can be clearly seen that the majority of publications appeared after 2011, and the research is getting more and more attention. Publications peak in 2014, 2018 and 2019.

Fig. 5 : 6 :

 56 Fig. 5: distribution of publications by year Fig. 6: Publications by Type of study

Fig. 7 :

 7 Fig. 7: Sample framework implementation strategy for corporate sustainability Source: [14]

Fig. 8 :

 8 Fig. 8: Sample of implementing recommendations for corporate sustainabilitySource:[START_REF] Gerner | Assessing and managing sustainability in international perspective: corporate sustainability across cultures -towards a strategic framework implementation approach[END_REF]

Data&

  Data collection: Most researchers employed two approaches: (a) Empirical Case Study. Scholars used qualitative indicators of performance. Case-study research is most effectively carried out through combining multiple techniques simultaneously (Gioia et al., 2013, p. 16; Jastram, 2012, p. 58; Prexl, 2010, p. 301; Scholz & Tietje, 2002, 3-4, 9 et seqq., 14, 15 et seqq., 23-25) [4]; (b) Theory-induced data collection, stakeholder observation, expert interviews and company resources for research in industrial area.

Table 1

 1 shows the review protocol.

Table 1 .

 1 Review Protocol

		"What are the thematic fields of research concerning social
	Review questions	LCA with integration to PLM?"
		"What gaps exist in research?"
		Social Life Cycle Assessment
		LCSA sustainability
	Keywords	Life cycle sustainability assessment (LCSA)
		"Social Life Cycle Assessment" + "PLM"
		"LCSA"+"Product lifecycle management"
	Sources for literature search	Google scholar | Semantic Scholar | Procedia CIRP 5

Table 2 :

 2 Distribution of publications by source.

Table 3 :

 3 Publications by countries

  Bohnsack, Marotzki, & Meuser, 2006; Flick, 2006, 2011; Kuckartz, 2014, p. 19; Lamnek, 2005; Mayring, 2002, 73 et seqq., 2014, p. 8; Scholz & Tietje, 2002; Silverman, 2013, 199 et seqq., 2014, 22 et seqq.). (Prexl, 2010, 301 et seqq.; Puls, 2016)

  focused upon corporate sustainability or sustainable entrepreneurship (Schaltegger & Wagner, 2011, 225 et seqq.; Weidinger et al., 2014), interchangeably, these facets are to be elaborated by means of case study. in his case study Sustainability performance is related to [a] an extended lifecycle analysis (LCA), and [b] the triad of marketing in business-to-business relations, business segments in sustainability contexts, and culture bound/intercultural notions of sustainability. His case study aimed at strengthening corporate sustainability with current and evolving culture-bound approaches. He provided guidelines for implementation at the operational level (Berns, Townend, Khayat, Balagopal, & Reeves, 2009, p. 7; Engert & Baumgartner, 2016; Khalili, 2011b, pp. 152-154) [4].

Based on a survey of LCA practitioners carried out in 2006 LCA is mostly used to support business strategy (18%) and R&D (18%), as input to product or process design (15%), in education (13%) and for labeling or product declarations (11%).

4 Retrieved from http://depts.washington.edu/matseed/mse_resources/Webpage/Bicycle/Material%20Selec-tion%20Process.htm

Procedia CIRP is an open access product focusing entirely on publishing high quality proceedings from CIRP conferences, enabling fast dissemination so that conference delegates can publish their papers in a dedicated online issue on ScienceDirect.


Stefan Adwernat
email: stefan.adwernat@ruhr-uni-bochum.de

Mario Wolf

Detlef Gerhard

An Ontology-Based Concept to Support Information Exchange for Virtual Reality Design Reviews

Keywords: Ontology, Interoperability, Virtual Reality, Design Review, RAMI 4.0

The current change of traditional products towards intelligent, connected cyber-physical systems (CPS) increases the amount of heterogenous data and models generated throughout the products' life cycle stages, starting from their development and reaching as far as reconfigurations in the product use phase. As CPS are highly modular and often customizable by the user, the management and decision support regarding product variants is critical. Mastering the vast complexity of these product-type and product-instance-related information has become one of the main challenges in modern engineering.

In previous works, the authors presented different mixed reality (MR) approaches as suitable tools to integrate product-related information and facilitate the interaction with digital contents such as product manufacturing information (PMI) and inspection characteristics for design reviews or real-time sensor values to support maintenance tasks.

This contribution proposes an ontology-based concept to facilitate the information exchange from distributed data sources for mixed reality usage and vice versa. The goal of this paper is to improve the information provision and interaction within a collaborative Virtual Reality-driven design review process for CPS. The ability of ontologies for querying and reasoning of linked information supports the comparison of design variants and feedback integration from design reviews of previous or existing product generations as well as allocating relevant design review metrics such as requirements, simulation results, costs or product use data. The capability of CPS to call upon services from other Industrie 4.0 components opens up a way to implement said ontology to meet today's engineering challenges.

Introduction

Throughout a product's life cycle, several validation and assessment tasks are performed on the product and its related processes and artifacts. Design reviews are essential for the quality assessment and troubleshooting in product engineering in this context, especially those using collaborative software approaches. According to IEC 61160 [1], design reviews are performed at different stages of the development process, mostly at project critical milestones to verify compliance with the previously defined requirements and aim to reveal potential deviations for correction at an early stage. The review usually involves an interdisciplinary team to address issues of all related departments in a collaborative process. Evaluated characteristics can be the product's overall impression, functionality, design and ergonomics, safety aspects, legal requirements, project timing, budgeting or production requirements and so on. In the end, a final status report documents the evaluation results along with possible countermeasures. The radical change from traditional products towards "smart" products or more precisely cyber-physical systems (CPS) emphasizes the need for a unified data acquisition and traceability approach, which supports the fusion of real and virtual systems [START_REF] Monostori | Cyber-physical systems in manufacturing[END_REF]. These cyber-physical systems have the ability to communicate and interact with their environment and other products by using Internet of Things (IoT) technologies and web-based services [START_REF] Abramovici | Systematization of Virtual Product Twin Models in the Context of Smart Product Reconfiguration during the Product Use Phase[END_REF], [START_REF] Vajna | CAx für Ingenieure[END_REF], with the consequence of an increased amount and heterogeneity of product related information. This significantly complicates the information exchange and provision for later usage. Another relevant aspect in this context is the user interaction with the provided information. Virtual Reality (VR) is generally suitable to visualize digital contents (models or data) for multiple users at the same time and allows for intuitive interactions within a completely immersive virtual environment. Therefore, VR contributes to information transparency and facilitates collaborative interactions with this information. A core challenge in review processes, not only for VR utilization, is the provision or availability of relevant information. Regarding VRsupported design reviews, information on the characteristics to be evaluated must be available. However, this information is usually created in different engineering authoring systems and therefore often lies distributed in different models, documents or databases, which is further amplified in the case of CPS.

The persistent storage of performed user interactions within the immersive VR environment is another typical weak point of VR applications that needs to be addressed in the context of design reviews. As mandated by [1], observed errors during a design review and their countermeasures must be documented according to legal responsibility. Moreover, the general traceability of results and performed actions is compulsory when companies are certified following DIN ISO 9001 [START_REF]Quality management systems -Requirements[END_REF].

As a result, the goal of this paper is to propose a concept that accommodates the aspects of information and knowledge exchange, context-specific provisioning for VR usage from heterogenous data sources with a specific focus on characteristics of CPS (i.e. use data from products in the field), a CPS-compliant data model and an overarching ontology to connect the entities in this context semantically. Based on this concept, user interactions in a VR-based design review can be recorded and their entities linked to allow a persistent record and therefore a consistent process documentation and traceability of actions, results or decisions made during the design review. Initiatives such as Reference Architecture Model Industrie 4.0 (RAMI 4.0) [START_REF]Referenzarchitekturmodell Industrie 4.0 (RAMI4.0)[END_REF] of the National Platform Industrie 4.0, the Industrial Internet Reference Architecture (IIRA) of the Industrial Internet Consortium (IIC), among other things, are intended to solve the problems of model fragmentation and their lack of semantic descriptions in engineering [START_REF] Lin | The Industrial Internet of Things: Volume G1: Reference Architecture[END_REF]. Since 2016, these initiatives have been cooperating with each other, resulting in a functional mapping that ensures compatibility between the approaches and their implementations [START_REF] Lin | Architecture Alignment and Interoperability -An Industrial Internet Consortium and Plattform Industrie 4.0 Joint Whitepaper[END_REF]. A prerequisite for the desired degree of interoperability in the context of VR design reviews using Industrie 4.0 methods is the introduction of a uniform digital representation for each product involved in the value creation process. The model of the asset administration shell (AAS) from RAMI 4.0 [START_REF]Referenzarchitekturmodell Industrie 4.0 (RAMI4.0)[END_REF] can be used to achieve this functionality. Each so-called asset is subject to a life cycle in RAMI 4.0 according to the usual understanding but differentiated by the life cycles of the product type and the individual product instances. An asset is a tangible or intangible object with value for the organization, regardless of whether it is a tangible product, a software component or a service. The information about an asset is stored digitally in the associated asset administration shell and made available for human-machine and machinemachine communication, so that a so-called Industrie 4.0 (I4.0) component is created as a combination between an asset and its administration shell (cf. Fig. 1). The AAS comprises a "Header" with identifying details about the asset and its associated AAS as well as a "Body" with a large number of sub-models, representing different aspects of the asset. Depending on the kind of asset, these aspects could describe manufacturing capabilities (e.g. drilling, assembling), the lifecycle status, condition states or similar type-or instance-based information. As part of the particular sub-model, proprietary data models (CAD data, source code etc.) are managed by a component manager, which can also provide interfaces to other I4.0 components [START_REF]Plattform Industrie 4.0.: Relationships between I4.0 Components -Composite Components and Smart Production, Working Paper[END_REF]. In this way, information can be interlinked between assets via the sub-models of their related AAS. The combination of I4.0 components creates new I4.0 components, i.e. a new asset with its own administration shell. This results in a recursive asset description that is able to map any granularity level [START_REF]Plattform Industrie 4.0.: Relationships between I4.0 Components -Composite Components and Smart Production, Working Paper[END_REF], from simple semi-finished products and individual parts to modules and components to complete systems and end products themselves, and to link them together by stored references. Recently, the National Platform Industrie 4.0 released a comprehensive guide on how to implement the asset administration shell in detail and with schema examples regarding (industrial) standards like XML, JSON, RDF, OPC-UA and AutomationML [START_REF][END_REF].

Knowledge Representation and Sharing

Several methods can be found in academic literature to represent and structure domainor organization-specific knowledge. For example, Taxonomies are used to classify and categorize terms, whereas Thesauri additionally describe their relationship through synonyms, hypernyms or hyponyms [START_REF]International Organization for Standardization: Information and documentation -Thesauri and interoperability with other vocabularies -Part 1: Thesauri for information retrieval[END_REF]. Semantic networks map concepts, terms and their relations into a graph that consists of vertices (concepts and terms) and edges (relationships) that link vertices to each other [START_REF] Quillian | Semantic Memory[END_REF]. Another common concept to represent knowledge are ontologies, which rest upon semantic networks, but are much stricter and more formal due to their axiomatic structure. Originally coined by Gruber [START_REF] Gruber | A translation approach to portable ontology specifications[END_REF], Studer et al. [START_REF] Studer | Knowledge engineering: Principles and methods[END_REF] define ontologies as "a formal, explicit specification of a shared conceptualisation". Therefore, ontologies are capable of modelling knowledge domains with complex, linked information structures as well as sharing and integrating heterogenous information originating from other domains. Due to axiomatic rules, ontologies allow for inferencing, i.e. new facts can be derived based on existing knowledge. In this context, the resource description framework (RDF) facilitates standardized data interchange through a textual formalization of resources and their properties expressed by statements in a triple structure (subject, predicate or property, object) [START_REF]RDF Working Group: Resource Description Framework[END_REF]. Using ontologies or RDF stores for CPS data is encouraged by the fact that the asset administration shell schemata are now available in [START_REF][END_REF] and [START_REF] Bader | The Semantic Asset Administration Shell[END_REF], so that a "common language" can be used between sub-models of different categories.

Virtual Reality Design Reviews

The motivation of the approaches described in the previous sections is to bridge the gap between physical and digital world by either bringing "intelligence" into products or linking information to products. Since VR is a suitable technology to visualize and interact with geometric 3D models in a virtual environment [START_REF] Wolfartsberger | Chances and Limitations of a Virtual Reality-supported Tool for Decision Making in Industrial Engineering[END_REF], it can contribute to this endeavor.

Virtual Reality not only supports immersion in design reviews but also for other engineering tasks it may lead to cost savings and improved and/or accelerated related processes. As concluded by Coburn et al. [START_REF] Coburn | A Review of the Capabilities of Current Low-Cost Virtual Reality Technology and Its Potential to Enhance the Design Process[END_REF], due to low costs and the high quality of modern VR devices, VR could become ubiquitous for several engineering processes and support everyday engineering tasks. In this context, many examples can be found in academic literature with the aim to support various engineering applications by incorporating VR. Referring to design reviews, Lawson et al. [START_REF] Lawson | Future directions for the development of virtual reality within an automotive manufacturer[END_REF] summarize that VR facilitates design verifications and the review process especially for physical prototypes and mock-ups can be replaced by its virtual counterpart, which in turn could lead to cost reductions for manufacturers.

Other contributions focus on improving user interactions within VR environments, such as Martini et al. [START_REF] Martini | A novel 3D user interface for the immersive design review[END_REF], who developed a hardware and software-based user interface to simplify interactions in VR review processes. Freeman et al. [START_REF] Freeman | CAD Integration in Virtual Reality Design Reviews for Improved Engineering Model Interaction[END_REF] investigate tools and methods for CAD-software-like interaction and manipulation functionalities for 3D models in VR. The fact that interaction in VR environments is generally simple and intuitive is confirmed by Wolfartsberger [START_REF] Wolfartsberger | Analyzing the potential of Virtual Reality for engineering design review[END_REF]. Their study on VR-supported design reviews indicates that the participants are more likely to detect errors in a 3D model within an immersive VR scene compared to a traditional CAD software approach on a PC screen. Additionally, performing the design review and interacting with the 3D models is described to be more intuitive and "natural" for non-CAD experts due to the high degree of immersion using VR head mounted displays (HMD).

In our previous works, we presented different mixed reality (MR) approaches as suitable tools to integrate product-related information and facilitate the interaction with digital contents such as product manufacturing information (PMI) and inspection characteristics for design reviews [START_REF] Adwernat | Mixed Reality Assistenzsystem zur visuellen Qualitätsprüfung mit Hilfe digitaler Produktfertigungsinformationen[END_REF] or real-time sensor values to support maintenance tasks [START_REF] Abramovici | Context-aware Maintenance Support for Augmented Reality Assistance and Synchronous Multi-user Collaboration[END_REF]. Our most recent contribution [START_REF] Adwernat | Optimizing the Design Review Process for Cyber-Physical Systems using Virtual Reality[END_REF] proposes a concept for a VR-supported design review process for CPS, taking their characteristics (e.g. use data of previous product instances) into account. This concept was prototypically implemented utilizing modern VR devices, with a clear focus on the collaborative review process, the visualization in VR and the intuitive user interaction.

In contrast to the approaches presented above, the paper at hand focusses on the aspects of information exchange and context-specific provisioning for VR-based design reviews in the light of CPS.

Approach

The main goal of this paper is to contribute to interoperability in the context of collaborative VR-based design reviews using the AAS of the relevant (virtual) components.

Another focus is the persistent storage of the user operations within the immersive VR environment in order to comply with documentation and traceability requirements demanded by IEC 61160 [1] or ISO 9001 [START_REF]Quality management systems -Requirements[END_REF]. To accommodate this, this section presents a conceptual framework based on Industrie 4.0 methods, starting with potential use cases addressed by the concept.

Considered Design Review Use Cases

Design reviews serve as an instrument for quality inspection and assessment at different stages of a product's life cycle. The main intention is to evaluate product or process related characteristics, usually in a collaborative manner to address issues from all related stakeholders. In a generic design review process according to [1] the operative tasks are accompanied by several administrative processes such as planning, preparation, execution and follow-up. Depending on the pursued objectives of the design review various kinds of information are a prerequisite for discussion and decision making.

Based on the authors previous works [START_REF] Adwernat | Optimizing the Design Review Process for Cyber-Physical Systems using Virtual Reality[END_REF], the considered use cases in this paper address VR-supported design reviews with a particular focus on cyber-physical systems, also known as smart products. As described above, CPS are characterized by the ability to communicate and interact with their environment and other products. Compared to traditional products, CPS therefore offer additional feedback information and services provided by the product instances and their "smart" components, as well as field reports from physical parts from a previous generation. This enhances evaluation possibilities for the product type under review especially for the development of an advanced product generation or when adapting existing designs.

In this context, the application of mobile VR technology with head mounted displays offers additional benefit. Firstly, it promotes the intuitive user interaction with the displayed information (textual or graphical) in virtual environments even across multiple sites and secondly, it allows for context-sensitive visualizations. As design reviews normally involve an interdisciplinary team, whose participants possess an individual role and function, specific content can and should be visualized for each individual user, for example mechanical simulations or cost overviews. The integrated visualization of relevant information can be used to simultaneously compare two design variants or to access real-time data from the product instances of a previous generation currently in the field.

Furthermore, individual user permissions can be derived, which restrict or allow user interactions during the design review. The same applies to a potential integration of external partners (customer or supplier), for example to clarify requirements or to take their feedback into account during agile review sessions. These participants should have only limited access for editing or viewing functionalities during the review process.

According to the standards ISO 9001 [START_REF]Quality management systems -Requirements[END_REF] and specifically IEC 61160 [1] regarding design reviews the documentation of organizational process is essential to maintain knowledge, make decisions reasonable and by this errors traceable. Therefore, the considered use cases also have to cover recording of user operation in VR, like adding a text note or highlighting individual parts.

Concept for Information Exchange in VR-Based Design Reviews

As detailed in the state-of-the-art section, initiatives like RAMI 4.0 or IIRA specify organizational frameworks and guidelines for these kinds of products or systems and introduce a uniform digital representation which contributes to interoperability. Therefore, this concept generally employs the model of the asset administration shell (AAS) from RAMI 4.0 [START_REF]Referenzarchitekturmodell Industrie 4.0 (RAMI4.0)[END_REF]. According to their definition, an asset represents tangible or intangible objects and the respective information is stored digitally in the associated AAS.

Transferred to this context, the main entities which have a specific AAS are the design review participants (user), the product to be reviewed (CPS 123) and the collaborative design review environment (VR-DR) as illustrated in Fig. 2.

Fig. 2. Concept for information exchange in VR design reviews

Each asset is associated with its corresponding AAS, which describes the asset in the information world. According to [START_REF]Plattform Industrie 4.0.: Relationships between I4.0 Components -Composite Components and Smart Production, Working Paper[END_REF], the AAS is composed of different sub-models, which represent different aspects of the asset (cf. Fig. 1). Here, the VR design review AAS (Fig. 2, top center) comprises specific sub-models to represent the general composition of the VR environment, available interactions with entities in VR as well as administrative capabilities to support the review process. In this regard, the differentiation between types and their instances must be noted. The type of an AAS (Fig. 2, top) serves as a structured template to derive an AAS instance with specific characteristics. For example, the AAS instances connected to the specific users "A" and "B" are created based on the generic user AAS type and holds individual information, such as identification, permissions and functions (see Fig. 2, left).

As described in our previous works [START_REF] Adwernat | Optimizing the Design Review Process for Cyber-Physical Systems using Virtual Reality[END_REF], the immersive VR design review allows for user interaction, such as manipulating objects and giving feedback via text input, voice recordings, graphical highlights or interactive polls. During review execution, the information about an individual user (stored in its associated AAS) serves as an input for the AAS of the active VR-DR session (Fig. 2, center). This allows to identify a user and provide specific information and permitted interactions. At the same time, performed interactions during the review session can be stored together with the authoring information. This data is maintained in the respective sub-model of the VR-DR AAS and later referenced by the AAS of the reviewed product or system. The various sub-models in the AAS of the reviewed product deliver additional input, that may benefit the review process. On the one hand, generic information related to the product type (e.g. 3D model, requirements associated with geometric features) have to be considered. In the case of developing advanced product generations or when adapting existing product designs, information of individual product instances in the field (operating or measurement data, maintenance data, fault reports etc.) can be additionally used during the design review, for example to discuss potential effects of operation conditions and agree on design alternatives.

Identification of Relevant Concepts and Terms

A prerequisite to build a comprehensive data model is the identification of key concepts and terms referring to the domain of interest. In this case, relevant terms of design reviews and collaborative VR environments in general have to be identified as well as specific terms derived from the considered use cases described above. In a first step, a taxonomy has been designed according to the subject areas. One goal of this paper is to establish a semantic connection of the entities representing VR-based design reviews for CPS. To achieve this, general categories for context-aware information supply were used to identify and allocate related terms. Shen et al. [START_REF] Shen | Information visualisation methods and techniques: State-of-the-art and future directions[END_REF] propose a classification of context concerning location, time, identity (user role), task or activity, used devices, available interaction capabilities, the distribution (of data), the type of data and according to privacy and security settings. Based on this, three main categories are suitable to classify relevant concepts and terms in the context of this paper: user-specific, administrative and technical aspects. The first category "user-specific aspects" summarizes terms which are related to the participants of VR-based design reviews and the considered use cases (cf. Fig. 3). At first, a distinction can be made between the different roles of a user, since participants may have different permissions in the review session, such as the moderator and guests. The same applies to the function of a user, which is linked to the respective department or if external participants (e.g. customer or supplier) are involved, too. The user's location delivers knowledge about the current time, which is an important aspect for distributed collaboration across multiple sites. Different permissions (e.g. create, read, update and delete) limit the user's access to objects or information within the VR environment. On top of that, a user's attendance, a name or identification may be attributed as well.

Fig. 3. Terms of user-specific aspects with exemplary characteristics

The second category "administrative aspects" addresses terms, which are connected to administrative characteristics of the design review. Among these, the collaboration type describes how the design review is performed. As mentioned in the use case description, the utilization of VR allows both, co-located and distributed collaboration as well as collaborating at the same time or asynchronously. The workflow progress captures the current stage of the design review, whereas the objectives have to be available as well.

Fig. 4. Terms of administrative aspects with exemplary characteristics

The third category "technical aspects" contains essential information for conducting VR-based design reviews (cf. Fig. 5). They refer to the product, like its life cycle stage, related technical documents or engineering data as well as data from the product's use phase (field data). Apart from this, a large portion of relevant information is delivered by the VR environment itself. As already mentioned, a common weakness of existing VR approaches is the lacking persistence of actions performed in VR. Based on the authors previous works [START_REF] Adwernat | Optimizing the Design Review Process for Cyber-Physical Systems using Virtual Reality[END_REF], the subcategories shown in Fig. 5 can be identified. The avatar related to a specific user is mainly described by its position in the virtual environment or room. This room in turn may have variable dimensions depending on the number of users in the review session, the scale of the reviewed part or even the amount of shared information during the review.

Fig. 5. Terms of technical aspects with exemplary characteristics

Further subcategories contain the used tools in review, such as text input, highlighting or redlining, as well as the objects for carrying the essential review information, e.g. the 3D model to be evaluated, virtual displays or free text for non-geometric information (including charts and figures), as well as symbols, curves or audio records for capturing annotations.

Semantic Data Model for VR-Based Design Reviews

The proposed concept (cf. Fig. 2) aims at facilitating knowledge exchange and contextsensitive provisioning for VR usage from heterogenous data sources with a specific focus on CPS characteristic. In order to guarantee a "common language", this concept generally employs the model of the asset administration shell (AAS) from RAMI 4.0 [START_REF]Referenzarchitekturmodell Industrie 4.0 (RAMI4.0)[END_REF]. Recent activities related to the AAS introduced RDF-or ontology-based concepts to promote semantic interoperability of Industrie 4.0 components. In order to comply with this, the proposed concept also rests upon ontologies for knowledge representation and sharing in VR design reviews (VR-DR). Due to the general nature of ontologies being modular and reusable by other ontologies [START_REF] Studer | Knowledge engineering: Principles and methods[END_REF], an integration with the aforementioned ontologies is given. Therefore, this ontology-based data model forms the basis to manage and exchange information between various data sources (engineering authoring systems, the products' operation data), the VR-based design review application and the participants of the review. This uniform data model serves as a reference for the integration of heterogenous information from and into the different systems.

In order to establish this data model, the identified concepts and terms in the presented taxonomies lay the foundation for modeling the VR-DR ontology by transferring concepts into classes or subclasses and related data properties. The main entities in the context of VR-based design reviews are the reviewed product, the VR-DR session itself and all participating users. These three entities build the top level class structure of the VR-DR ontology shown in Fig. 6. For reasons of clarity and comprehensibility, Fig. 6 illustrates only an excerpt of the complete ontology with exemplary classes and relationships.

According to the definition of RAMI 4.0 [START_REF]Referenzarchitekturmodell Industrie 4.0 (RAMI4.0)[END_REF], the generic types of the three entities "product", "VR-DR" and "user" are associated with an AAS, which is inherited for the specific instances. As described in section 2.1, the exchange of information between assets is performed via sub-models of their respective AAS (cf. Fig. 1). For example, the reviewed product is represented by a 3D CAD model, which can be part of a "Mechanical CAD" sub-model in the product's AAS. On the other side, the VR-DR is also associated with an AAS, where one of the sub-models represents the aspects of the VR environment. One entity within the VR environment is the product's "VR model", which corresponds to the product's tessellated 3D CAD model, i.e. after conversion of the native model (cf. Fig. 6). This implies, that two different models are considered in each AAS, but a semantic mapping between them is established. The same applies to a VR avatar, which represents a user in the VR-DR session and a real person in the physical world. In this way, the entities of the respective sub-models can be connected according to their relation properties, for example a "USER" "creates" a "TEXTNOTE" (see Fig. 6).

Based on this approach, the VR-DR ontology enables a common understanding for the mapping of different components or sub-models, when referring to the definition in RAMI 4.0 [START_REF]Referenzarchitekturmodell Industrie 4.0 (RAMI4.0)[END_REF]. Finally, the ontology was implemented using the software Protégé.

Conclusion and Outlook

Today, VR is a common tool for several industrial tasks, which focus on immersive visualization and user interaction. Nevertheless, the necessary information is often integrated statically and isolated. The knowledge that is created during a VR session is also rarely available afterwards. current shift towards increasingly connected CPS in the era of Industrie 4.0 leads to ever larger amounts of information. RAMI and its AAS delivers a framework for a uniform digital representation of so-called assets, which contributes to interoperability between the assets. The presented concept employs the AAS model to support information exchange and persistence especially in the light of VR-based design reviews for CPS. As a first step, the knowledge formalization is achieved with the help of an ontology. Since ontologies are suitable for sharing knowledge about a specific area with other ontologies, the specific knowledge is not only limited to this concept, but can be reused at other stages of the product life cycle or for different applications as well.

Currently, the authors work on implementing a complete asset administration shellbased demonstrator of a smart factory training model from a German industrial education supplier. This demonstrator includes the holistic AAS representation of all the production system's components, organizing the communication between those components via OPC-UA through services in the AAS, tracking and tracing of the products via their administration shells and finally connecting both virtual and augmented reality frontends to monitor current and aggregated data directly on either the physical or virtual representation of production system or product. To facilitate the exchange of information between a variety of engineering authoring systems, the production system (representing a CPS) and the virtual or augmented reality applications, the ontology will be transferred into a graph database that supports reasoning of RDF stores.

This demonstrator case will then be used as a cyber-physical use case for the VRbased design review, giving us access to real operational data of the produced products and production system itself and yielding the opportunity to embed the VR design review data into existing asset administration shells.

Fig. 1 .

 1 Fig. 1. Basic structure of the asset administration shell and I4.0 component -based on[START_REF][END_REF]

Fig. 6 .

 6 Fig. 6. Excerpt of the ontology implemented in Protégé

4

 4


domain: spi info

text:
Piers Barrios
email: piers.barrios@utc.fr

François Loison
email: francois.loison@gfi.world

Christophe Danjou
email: christophe.danjou@polymtl.ca

Benoit Ey- Nard
email: benoit.eynard@utc.fr

PLM migration in the era of Big Data and IoT: analysis of information system and data topology

Keywords: Product Lifecycle Management, Internet of Things, data package, group clustering

As product lifecycle management is starting to be a standard information system in most companies, a data manipulation issue starts to emerge. Indeed, the information contained in a system often needs to be accessible or even transferred to another one to exploit a new software's functionalities. With the Big Data era, new methods of analysis start to emerge, and the graph visualisation of data enables a better human understanding of the data itself. We propose to address the PLM migration issues with a new approach based on analysis of information system and data topology. The data is passed onto a graph and bundles are made thanks to clustering algorithms; this bundling enables a better understanding of the data and ease migration. However, PLM has links between links which complicate the transition to graphs. Finally, the described use-case proves that data bundling eases the data migration and prevents some usual pitfalls and delays.

Introduction

Information and communication technology (ICT) systems are in constant evolution to manage more information, improve the user interface or enable new features. However, data migration remains a core problem when going from one software package to the next. It can be mitigated by keeping the same software editor and doing regular updates, but this is too costly compared to keeping the system intact for many years and doing a brutal upgrade. An upgrade often means a major change in the data model in between the source and the target. To address this complexity, most of ICT systems' upgrades are conducted by three main actors: the industrial, client of this upgrade; the software editor of the target system and the integrator, the company that makes sure that the software will fit the industrial's needs. In the context of Big Data [START_REF] Dekhtiar | Deep learning for big data applications in CAD and PLM -Research review, opportunities and case study[END_REF] and emergence of Internet of Things (IoT) [START_REF] Barrios | Towards a Digital Thread Between Industrial Internet of Things and Product Lifecycle Management: Experimental Work for Prototype Implementation[END_REF], PLM data needs to be easily accessible in the context of a data migration to be efficiently used by these emerging technologies. However, until now this is not the case and we aim to reduce the gap in this domain by proposing a method to ease data migration.

An upgrade process can be split up into multiple streams (Fig. 1):

 The applicative stream concerns the user interface, the behaviour and the data model.  Data migration stream produces a method to migrate data as well as executing it.

 Interfaces stream ensures the link with external applications.  Infrastructure stream tackles the IT infrastructure needs for the app to function.

 User experience and acceptance stream manages the change and the user acceptance of the new system.  Finally, pilot and system engineering stream ensure the constraints and interactions in-between the different streams.

Fig. 1. ICT system upgrade decomposition into streams

Managing a product's lifecycle is quite a tenuous task as it goes from its ideation to its disappearance. In this regard, Terzi [START_REF] Terzi | Product lifecycle managementfrom its history to its new role[END_REF] defines Product Lifecycle Management (PLM) as follows: "PLM can be broadly defined as a product centriclifecycle-oriented business model, supported by ICT, in which product data are shared among actors, processes and organisations in the different phases of the product lifecycle for achieving desired performances and sustainability for the product and related services." » Nevertheless, ICT, only being there to support the PLM process and methodologies, has gained an increasing impact in recent years to the point where vendors are now providing "PLM software" aiming to encapsulate all the necessary components for a properly functioning process and even methodologies.

Compared to other ICT systems such as MES or ERP, PLM data migration is fundamental in PLM systems as the data needs to be available throughout the existence of the product's instances. In some cases, such as major aircraft companies, the legacy PLM system needs to remain available causing huge impact on IT costs. Indeed, the knowledgeable personnel tends to retire earlier than some of the products on the market; hence the resource gets rarer and incidentally more expensive.

In this regard, one could easily conclude that it would be cheaper for a company to do a migration than to keep legacy systems up and running. However, going from a legacy system to a top-of-the-pop system implies the successful migration of the existing data.

Overall, implementation of a data migration process is challenging because:

 The data migration strategies are plenty and dimensioning for any project. Unfortunately, theoretical reality that can be far from data's reality. To our knowledge, there is no specialised software to evaluate data migration strategy.  Initial resource estimation tends to underestimate the complexity of data migration because of no direct or visible added value for the trade and users.  Data migration stream has a transient statei.e. data migration elaboration -followed by a steady state. During elaboration, complexity is very high because of impact of other streams and organisational make or buy choices. A tooled-up method intended to reduce this complexity is needed.  Finally, the triptych of application, data migration and user acceptance are strongly interdependent and tends to destabilise the project and the global system.

Most often, the migration isn't going from one legacy system to one target system but from multiple sources to one target associated with important data volumetry. Data extraction may require to only migrate part of a system's data as that data is not relevant anymore or should be migrated towards another system. Also, on the data migration stream, there are no established methodologies to tackle such a complex task as there would be on other streams; e.g. Waterfall, Scrum. Therefore, to address this issue, our article will be structured as follows: we will focus our state of the art on interoperability and PLM data migration. The methodology proposition will underline the issues faced and the choices made to attain a usable solution. This proposition will be illustrated by use cases inspired by our industrial experience. Finally, discussion, conclusion and future works will complete this paper.

2

State of the art

Interoperability

The European interoperability framework [START_REF] Chen | Architectures for enterprise integration and interoperability: Past, present and future[END_REF] defines three dimensions for interoperability: technical, semantic and organisational. Technical interoperability is composed mostly of all the communication protocols and infrastructure that enable various systems to communicate. Semantic interoperability is the key one here; it "is the ability to automatically interpret the information exchanged meaningfully and accurately in order to produce useful results as defined by the end users of the systems under consideration" [START_REF] Özacar | ANEMONE: An environment for modular ontology development[END_REF]. Finally, organisational interoperability is concerned with people that wish to exchange information and may have different internal structures and processes. PLM's ICT systems are, until now, made to address semantical interoperability as they add sense to data for the various trades working on the products; people within the same company may achieve semantic interoperability through their access to PLM. ISO 14258 [START_REF]Industrial automation -Concepts and rules for enterprise models. International Organisation for Standards[END_REF] says that semantic interoperability can be achieved in three ways:  Integrated: "With integrated models there is a standard model form." The main limit there is the standardisation of models.  Unified: A meta-model exists to represent all existing models. Hence, one can establish correspondence between the various models.  Federated: Models are diverse and rely on the establishment of dynamic correspondence.

PLM migration from multiple initial systems to one target system can be considered as one way to achieve integrated semantic interoperability. Hence, enabling a better understanding of data migration could enable, in a near future, the transition of integrated systems towards a unified or even a federated ICT system. However, we need to better understand what has already been done concerning PLM data migration.

On data exchange and interoperability, one might look towards one of the following for extended state of the art: Rachuri et al. [START_REF] Rachuri | Information sharing and exchange in the context of product lifecycle management: Role of standards[END_REF], Fortineau et al. [START_REF] Fortineau | Improving the interoperability of industrial information systems with description logic-based models-The state of the art[END_REF] and Sriti et al. [START_REF] Sriti | Ontology-based approach for product information exchange[END_REF].

PLM data migration

Research review through Scopus and Web of Science highlights the following:

 In Müller et al. [START_REF] Müller | PLM-Based Service Data Management in Steam Turbine Business[END_REF], "PLM migration project" is only in the abstract; in the rest of the articles, the authors talk about "PLM deployment". Unfortunately, data migration is not mentioned throughout this article. However, project management in interestingly discussed in one paragraph, providing precious insight about the management of such projects: Even if led by equal rights between the business unit and IT, PLM upgrade still had been perceived as a pure IT project.  Singh [START_REF] Singh | Migration of PLM systems to cloud[END_REF] challenges only the transition to the cloud and does not address data migration itself. It is understood that this is an isomorphic migration and that systems are unlikely to evolve between on-premise PLM and cloud PLM. Unfortunately, experience has proven otherwise as PLM migration always implies upgrade.  Renji Kuncheria [START_REF] John | PLM implementation at MAN Diesel A/S: a case study[END_REF] stresses out key points of data migration, without however tackling them, in these terms: "Migration of data from legacy enterprise data-systems is one of the important and challenging tasks for most PLM implementations.

[…] Moreover, the dependency of production activities on data, that is complete and accurate, stresses the importance for error free data migration. Translating data stored in formats as required or limited by legacy systems to conform to the PLM system specifications only adds to the complexity." However, throughout the article the actual data migration process is neither explicated, nor detailed.

In order to address product development, Guérineau et al. [START_REF] Guérineau | Agile and Project-Planned Methods in Multidisciplinary Product Design[END_REF] proposes a four-level categorisation for product development. However, none of the listed artefacts enables us to tackle the data migration stream of an ICT system upgrade from the multiple source applications into a unified target application.

Methodology Proposition: Data Systemizer

To challenge the previously cited challenges, we propose a standard reusable methodology for data migration stream. The applied approach consists in decoupling a complex problem into several simpler problems, while controlling the interdependencies between the sub-problems. Applied to data transformation issues, this principle amounts to breaking down the dataset into the most independent data islands possible. First, we will explore the data model before exploring the data clustering and the existing interface.

Concise and Generalised Data Model

As PLM systems try to encompass as much information on the product as possible, the number of entities and number of attributes per entity is staggering. As a global understanding is key to making accountable choices, only a few elements are useful to understand the system from one point of view. For a decisional tool such as Data Systemizer, the model must be restricted to entities and attributes that are mandatory for analysis, i.e. entities and attributes driving data clustering. Therefore, we will base ourselves on a concise part of the data model. PLM software tends to consider the various instances of an object separately. For instance, one may consider that a part is spread over several entities such as engineering part and manufacturing part for instance. In this case there is no such thing as a part by itself. To better approach a model, we proceed to a reification meaning that we consider all the parts as actual parts and process information on them: all parts attributes are now considered similar. Generalising the model eases the analysis a great deal and the definition of analysis rules.

Data Model Structuring Choice

Indeed, the PLM data is more than often stored in a relational database for speed and reliability purpose. However, graph databases take benefit from these similarities to propose full-featured graph applications with interfaces including real world object/link-based data.

In this regard, we consider switching the data stored into PLM towards a graph. In the graph theory, everything is either a vertex or an edge and an edge is necessarily between two vertices. In PLM, any artefact is either an object or a link. An object is a standalone entity holding attributes and a link is an entity relaying objects, generally 2 objects identified by their role; links can hold attributes. As one may realise, PLM data model systems have strong similarities with graph theory models. However, PLM application usually push-up the limit by considering links on links. When including these, the model is no longer comparable with the graph theory as a vertex cannot connect a node and a vertex. chip. The ability of replacing SMD chip by DIP chip is not global but is constrained by a validation. Equivalence link enables replacement for the specific PCB/SMD chip association. This is a "link on link" as DIP chip is connected to structure link. Replacement is enabled only for this specific PCB / SMB chip assembly.

Fig. 2. Data Model illustration

Gutwenger et al. [START_REF] Gutwenger | Inserting an Edge into a Planar Graph[END_REF] and Farhadian [START_REF] Farhadian | A Coordinate System for Graphs[END_REF] propose solutions to convert such "links on links" model to a graph. However, it requires a virtual node splitting the vertex in two, the "link on link" vertex being connected to this virtual node. This approach is suitable for presentation (sketching the model into a graph). At this point, it is not compatible with clustering as the virtual node does not belong to any cluster. However, to enhance analytics on the data, clustering is essential.

We therefore shift towards an Entity/Link model: Entity is either an object or a link and Link is a link between 2 entities. This model allows implementing links on links between objects. Recursive definition of link allows more sophisticated constructions: "links on links between objects and links" for example. The Entity/Link model has an impact on clustering and tree traversal consolidation processes (Breadth-first search, Depth-first search) needed, for example, to apply metrics on clusters; e.g. counting entities. Basically, clustering allocates entities to lots, while remaining links are stored into a link between lots called a Lot Dependency. Lots and lot dependencies are also entities that can be processed by a further clustering pass.

In the end, everything is an entity. We can distinguish different classes of entities depending on the sophistication; as follows:

Element Entity class Object or Link Entity [0] Lot or Lot Dependency containing Entities [0] Entity [1] Lot or Lot Dependency containing Entities [1] Entity [2] … … Lot or Lot Dependency containing Entities [N-1] Entity [N] In the case where there are no links on links, lot dependencies allocation calculation and tree traversal processes are nominal. In the case of links on links, issues are raised because nominal algorithms raise precedence problems; e.g. entity accessed but not yet initialised. We define an ordering metric called LinkLevel such as:

LinkLevel ( object ) = 0 (1) LinkLevel( link ) = LinkLevel( edge A entity ) + LinkLevel( edge B entity ) + 1 [START_REF] Barrios | Towards a Digital Thread Between Industrial Internet of Things and Product Lifecycle Management: Experimental Work for Prototype Implementation[END_REF] Links are sorted by increasing LinkLevel and are processed one after the other, starting by LinkLevel 1. This approach sorts out the precedence issues explained previously. Our model also contains Virtual Entities which are not taken into consideration by the clustering process. As circuits (loops of directed vertices) are an issue, we isolate them as such. These are present in the final graph, while clustering remains unchanged [START_REF] Johnson | Finding All the Elementary Circuits of a Directed Graph[END_REF].

To summarise:

 We implement an Entity/Link data model which is not a graph model  The model is completed to allow further lot clustering by a meta-model containing lots and lot dependencies; a lot is an entity and a lot dependency is a lot link  Bridges to graph model exist for clustering entities into lots and lot dependencies & sketch graphs for presentation  Entity/Link data model raises tree model traversal precedence issues, a metric called LinkLevel allows to correctly order links processing

Clustering

Zhong et al. [START_REF] Zhong | Evolution Supporting Class-Cluster Data Model for PLM[END_REF] explored the possibilities of putting part of the PLM data into clusters in order to increase relevancy and flexibility. However, PLM data migration was not addres sed. The most important success factor of PLM migration is choosing the right data transformation strategy. Successful data transformation strategies go as follows:

 Loosely coupled data lots to allow to parallelise data lot processing.  Most possible functionally significant data lots: a data lot and its dependencies should contain a business product to foster validation tests. On the contrary, a lot dividing strategy based on bottom/up layers such as bolt & nuts, assemblies, modules and end items is not acceptable because it's testable only at the end of migration.  Lots should be decomposed in a loosely coupled lot tree in order to recourse this process at lot level and build efficient test lots given a size and error rate.

Clustering is the key to achieve these needs. The clustering is realised by a "Lot Divider" which takes entities as input and output lots and lot dependencies partitioning entities. There are two categories of Lot Dividers:

 Business Lot Divider: driven by functional parameters available from data. For example divide data by program name, divide data by site name.  Mathematical Lot Divider: driven by graph topology, requires no business parameters. E.g. Metis Lot Divider partitions a graph in sub-graphs while reducing subgraphs dependencies; Adherence Lot Divider creates sub-lots to understand and measure lot adherence; Bill of Material (BOM) Lot Divider groups entities until an entity is re-used.

Both dividers produce lots who have a type that could be Business or Technical. Lot type drives further passes of dividing as explained in next chapters. By default, Business Lot Dividers produce Business Lots and Mathematical Dividers product Technical Lots but this default settings can be overridden by parameterization depending on clustering strategy needed. Metis [START_REF] Abou-Rjeili | Multilevel algorithms for partitioning power-law graphs[END_REF] is a graph partitioning tool taking as input a graph and desired number of partitions N. It produces N sub-graphs optimised to reduce number of cross-partition vertices. Metis is used by "Better than Big Bang Divider" intended to split data in most possible number of independent lots, to reduce data migration complexity.

The experimental approach is based on scenarios. A scenario is a pipe of Lot Dividers that allocates data entities [0] (objects, links) to entities [M] (lots and lot dependencies), M being the number of clustering passes. Scenario outcomes are evaluated by verifying they are compliant to rules enounced previously. Data Systemizer defines a lot type: business or technical. Whatever the Lot Dividers execution sequence is and their numbers, the lot aggregation chain is always a business lot chain followed by a technical lot chain: Fig. 3. Example of sequence of processing Fig. 3 introduces lot inclusion chains given the Entity Level (EL). In this example four levels are retained. Each lot is noted as included (UML) in the previous one. The deducted properties are as follows:

Entity [EL] = { Object, Links } for EL=0

(3) Entity [EL] = { Lot, Lot dependency } for EL≥1 (4) An entity with EL=N+1 contains entities EL=N : Entity [EL+1] = { Entity [EL] } (5) The clustering pipe is then executed as following:

1. Identify min( ELBusiness ) and max( ELTechnical ), the EL directly preceding (business / technical lots) break. From example: min( ELBusiness ) = 3, max( ELTechnical ) = 2 2. For each Business Lot [min( ELBusiness )] : a. Allocate to a dedicated working space (bench) the Lot Divider with Entities [max( ELTechnical )] belonging to current Business Lot b. Run the Lot Divider algorithm using bench entities as input. Lots produced by Lot Divider are either Business or Technical (functional parameter of scenario). They are attached as direct children of current business lot. 3. Run the Lot Divider with Entities [max( ELTechnical )] as input Throughout this section, we set out all the necessary artefacts and tools necessary to dive into PLM systems' data; we shall now consider the use cases this methodology can be applied to.

Needless to say, Data Systemizer is data format agnostic. I.e. a data format such as XML imposes a structure whereas the analysis detailed here is agnostic and able to explore multiple structures. Hence, the flatter the format, the better. The contribution of a format such as XML in this case is grammar and completeness verification, which is nice but remains optional.

4

Use-case

Optimizing an ETL Data Load

ETL (Extract/Transform/Load) tools aim to migrate data from source to target system by applying a pattern. However, it is flow driven and unaware of data topology, e.g. decomposition of data in loosely coupled lots. Some approaches to ETL processes such as [START_REF] Simitsis | Graph-Based Modeling of ETL Activities with Multi-level Transformations and Updates[END_REF] in the data warehouse and big data contexts might be and semantic however these do not fit the PLM needs as expressed here.

During ETL elaboration, loading error rate may be dramatic for PLM data structures because of the re-use object factor -an object is re-used by other objects through a link.

If the re-used object loading is broken, all dependent links and all recursively dependent links will fail, a.k.a. explosive errors spreading. As a result, data is not business testable and the error analysis task is complex because valuable error root causes are flooded by useless dependent errors. Data Systemizer can extract a "successful transformation data strategy" and drive ETL. Fig. 4 presents interfaces in the black-box manner. Data is input via CSV or XML files, clustered by Data Systemizer and then output. On this interface, the various clusters are going to have their own files; hence enabling smooth input to ETL solution for the new PLM system. ETL is fed by data lots respecting the original data format, not full data from the input. After lot loading is processed by ETL, Data Systemizer gets objects, link errors and inspects impacts of errors. If explosive errors spreading phenomena are detected, loading is stopped for dependent lots while independent lots continue to load.

Moreover, output can be a graph; this is helpful as it enables meaningful insight of data; it enables company and project leaders to understand and anticipate possible issues; they will be able to evaluate the right complexity of the data transfer. Also, it sometimes underlines the fact that the theoretical truth about the data is far from reality.

Optimizing a migration strategy

A data migration project needed to evaluate migration strategy of data package containing 10 million objects and links. ETL direct approach had failed because of "explosive errors spreading" phenomenon and the duration of a test increment which was too long to bear iterative development mode.

Data is extracted from a PLM source system. Data extraction has been made by source object types into a set of CSV flat files. Files data sets are not organized by programs nor any business organization. Loading data type by type in a Big Bang migration strategy is not acceptable because this loading strategy would be testable only at end of process and subjected to cascading errors phenomenon. The question raised was: Is there a more optimal than the Big-Bang migration strategy? Data Systemizer was parameterised to perform two BOM Dividing and Metis BOM Dividing: Fig. 5. Result of Data Systemizer application: data is separated in 12 different lots Fig. 5 shows input data which has been clustered into 12 lots; 11 separated lots all depending on a single component lot. Data Systemizer can restitute this monolithic data package in 12 lots. The lot in orange contains some data referential integrity errors; i.e. orphan links. Some elaboration specific test data lots can be provided given needed volumetry and error rate. Test data lots are functionally significant, they contain testable end-to-end business data.

Choosing right migration strategy

An aircraft company needs to migrate a certification application from a PLM system to an ERP system. Volumetry is low but data model is complex. Drastic system changes and model complexity requires important end users testing hence big-bang migration is not acceptable because on one hand, it would retain tests at the end of the migration project and on the other end, users would redo costly tests.

To enable a fine-grained migration strategy, two lot dividing strategies are studied: at Family level (top level) and at Baseline level (middle level). Business users would like to know what level is best.

As data model is complex, some specific algorithms have been developed to extract Family and Baseline information. Two graphs are produced to compare both migration strategies. To see if data could be split at lower level, the baseline level analysis has been run. wastes the benefit of baseline-level migration strategy. In this case, the study shows that Family level migration is best choice.

Conclusion and future work

This article has outlined the issues related to PLM data migration as well as why this is crucial regarding being able to tackle one company's own data in the current context of Big Data. Methodology was described and use cases improving existing were outlined. Discussion focus on possible reusability of the underlined methodology as well as possible improvements. Indeed, the method outlined could be reused in any information system whose object representation is similar, such as ERP, MES or IoT platforms. Improvements to the method could be made regarding the treatment of circuits. Indeed, they are currently temporarily put away to avoid blocking the process. However, in some scenarios, their number would be too non-negligible, and one would need to tackle them head on. Also, improvements would be made on the implementation and focus on enabling user-friendly interfaces.

Future works should tackle measuring the effectivity increase thanks to the use of this method which would be necessary to leverage further deployments.

Current work could we improved according to the following directions:

 Some real-life examples such as Fig. 7 show data graphs with lots highly coupled. The raw question is to know whether highly coupling is intrinsic to data topology or to weakness of clustering algorithm. A tooled-up method able to inspect graph coupling quality would be helpful.  This article deals with data loading use cases. They are other interesting use cases: modification and purge/archive. Modification use case implies a 2 ways data analysis: data to process versus data present in the system. Purge/archive use case is interesting in PLM systems because data are highly linked to other data. Scoping the purge/archive target is challenging, executing purge/archive is even more complicated. Deletion use case is a simpler subcase of purge/archive, still not achievable manually.  Data verification after migration. Current industry practice is based on end users' tests. This practice should be improved. Current directions are: probability and statistics-based method to provide a more controlled confidence level to tests executed, mode-based approaches relaying entity counts to reconciliate number of entities before and after migration, brute force export after migration and comparison with source data.

Fig. 2

 2 illustrates data model. It shows a Printed Circuit Board (PCB) accepting a Surface Mount Device (SMD) chip. Both are objects. PCB contains pads for SMD chip, it is materialized by a structure link. To prevent component shortage issues, PCB has a dual option loading, its pads can accept a SMD chip or a Dual Inline Package (DIP)

Fig. 4 .

 4 Fig. 4. Interfaces of Data Systemizer in the ETL Use-case

Fig. 6 .

 6 Fig. 6. Partial graph of Family level migration strategy Fig. 6 shows graph corresponding to Family level migration strategy. Family lots are totally separated, this migration strategy is efficient.To see if data could be split at lower level, the baseline level analysis has been run.

Fig. 7 .Fig. 7

 77 Fig. 7. Partial graph of Baseline level migration strategy