Yan Lu
email: yan.lu@nist.gov

Frank Riddick
email: frank.riddick@nist.gov

Nenad Ivezic
email: nenad.ivezic@nist.gov

The Paradigm Shift in Smart Manufacturing System Architecture

Keywords: System architecture, Smart manufacturing, Cyber physical production system, Service oriented architecture

des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

In the current market, customers call for products tailored to their particular needs. Manufacturers seek to meet the demand for these products, but many current manufacturing systems cannot meet the increased requirements for product customization at mass production rates that are profitable. Yet, advanced manufacturing methods, such as 3D printing and flexible production, are emerging with the promise to make highly-personalized production at scales both possible and affordable. Simultaneously, rapid advances in information and communications technologies (ICT) are being applied to manufacturing systems, driving a shift from traditional labor-intensive processes to advanced-technology-based processes 0. This on-going integration of ad-vanced manufacturing methods, operation technologies (OT), and the ICT technologies, is fueling the current Smart Manufacturing (SM) trend to enable systems that can respond in real time to meet changing demands and conditions in the factory, in the supply network, and in customer needs 2. Historically, manufacturing systems have been designed to follow the Purdue Reference Model for Computer Integrated Manufacturing 2, which was standardized in ISA954. The ISA 95 model includes 5 levels of manufacturing functions that are often implemented as logically separated layers of applications or systems. Specifically, lower level systems (0, 1 and 2) and higher levels applications (3 and 4) are separated into the OT1 and information technology (IT) domains. The legacy architecture has been widely adopted and implemented in last 30 years accompanied by hierarchical, diverse and domain specific communication structure 7. However, under the legacy architecture, not only is integration between IT and OT difficult, but skip-level function integration is not supported, which makes it too rigid to adapt rapidly to evolving opportunities from ICT technology integration. For example, in the Internet of Things (IoT) world, every part of a manufacturing enterprise is designed to be connected on the internet so that communication, integration and automation can be achieved without constraints. In addition, cloud and mobile computing enable manufacturing functions once implemented at different levels of the hierarchy to now be available without even knowing where they are hosted. Smart components and smarter systems on the shop floor can run advanced analytics and simulations, and make decisions beyond the lower functions defined in ISA 95.

This suggests that a new, information-centric architecture is needed in order to realize ICT's full potential for SMS and facilitate transformation of closed or proprietary manufacturing system architectures into networks of cooperating manufacturing components so as to attain higher degrees of flexibility and integration. This paper provides a study of the architectural impact of ICT on a manufacturing ecosystem and proposes a service oriented architecture that leverages the benefits of ICT and safety and security requirements from the manufacturing OT domain.

The rest of the paper is structured as follows. Section 2 defines a manufacturing ecosystem to scope our research followed by a description of the legacy architectural model based on ISA 95. Section 3 describes the key ICT technologies identified that contribute most to the SMS architecture paradigm shift and presents their architectural impacts on SMS. In Section 4 we propose a new SMS reference architecture. Key challenges of implementing such an architecture are presented. Section 5 concludes the paper with future research direction.

SMS and the Legacy Architecture

Smart manufacturing encompasses a broad scope of systems in a manufacturing business including production, management, design, and engineering functions. The collection of hardware components, their related software components, and the support applications that make up a manufacturing enterprise are what we term the smart manufacturing ecosystem 45. Figure 1 illustrates three dimensions of concern that are manifest in the smart manufacturing ecosystem. Each dimensionproduct, production system, and businessis shown within its own lifecycle. Each of these dimensions comes into play in the vertical integration of machines, plants, and enterprise systems in what we call the Manufacturing Pyramid. The Manufacturing Pyramid, in the center of Figure 1, is often referred to as the manufacturing system and implemented based on the ISA 95 model. The ISA 95 standard defines a 5-level model for activities in the manufacturing enterprise. Each level provides specialized functions and has characteristic response times 7. Level 0 and Level 1 define field-level activities including the actual physical production process and the sensing and manipulating of the process. Level 2 defines the functions of monitoring, automated control, and supervisory control of the production process, which usually are performed by programmable logic controllers (PLC), distributed control systems (DCS) and/or supervisory control and data acquisition systems (SCADA). Level 1 and Level 2 communicate within time frames on the order of hours, minutes, seconds, and sub-seconds. Level 3 defines the Manufacturing Operation Management (MoM) activities of work flow and stepping the process through states to produce the desired end products. It deals with maintaining records and optimizing the production process. Level 3 deals with time frames of days, shifts, hours, minutes, and seconds. Level 4 defines the Enterprise Resource Planning (ERP) activities to establish the production (master) schedule (i.e., what to produce, which materials to use, where to deliver the product, and how to ship it there). It deals with determining inventory levels and making sure that materials are delivered on time to the right place for production. Level 4 deals with time frames of months, weeks, days, and shifts.

While the ISA 95 model is used widely to support the definition of architectures for manufacturing systems, recently some drawbacks with its use have emerged 7. These drawbacks include:

1) Integrating systems across level boundaries is difficult due in part to the use of different network technologies on different levels. 2) Integrating between Supply Chain Management (SCM), Customer Relation Management (CRM), and Product Lifecycle Management (PLM) activities on different ecosystem dimensions is not supported. Various methods have attempted to deal with the drawbacks of systems architected based on the ISA95 model. Some software vendors and system integrators have provided solutions focused on the vertical integration of manufacturing components in the manufacturing pyramid to enable advanced controls at the shop floor and optimal decision making at the plant and enterprise. Efforts have also been observed that focus on exchanging information between manufacturing ecosystem dimensions, such as continuous process improvement (CPI) programs, flexible manufacturing systems (FMS), and design for manufacturing and assembly (DFMA) approaches. Some lean enterprise efforts connect SCM with ERP to reduce inventory and enable demand-based manufacturing 5. However, these individual efforts fall short in providing widely applicable methods for integration within and across the three ecosystem dimensions required for SMS. The combination of these perspectives requires a new reference architecture.

Architectural Impacts of ICT Technologies

For our study, ICT technologies are classified in three clusters: (1) digital technology including digital thread, product/production/process modeling and simulation, knowledge management, and visualization; (2) infrastructure technology including IoT, big data and advanced computing; and (3) Smart systems technology involving Cyber Physical Production System (CPPS) and service-oriented architecture. All technology of the three clusters contribute to the paradigm shift from the legacy architectures to a new SMS architecture. Each cluster is described in the sections below.

The Impact of Digitalization

An enormous amount of information is generated and used during the product, production system and business lifecycles. This data might be used to ensure customer requirements are met, to assess product and process performance, or to meet environmental reporting requirements. Digitalization is the process through which information about the product, processes, and production chain are rendered in a digital form that can be archived, exchanged, or analyzed electronically. Digitalization capabilities help manufacturing companies create virtual representations of their products, assets and processes, exchange large amounts of data rapidly, store data efficiently, enrich processes with digital expert knowledge, generate valuable insights from analyzing "big data", and facilitate communication and collaboration through digital channels within their value chain 9.

The pervasive adoption of digital technology will have two dominant impacts on SMS and their architecture. 1) There will be an increase in the availability of collaborative environments for product development. Their architectures will exhibit a tighter integration of PLM, ERP, MES, SCM, CRM and asset management functions. These platforms will enable customers and suppliers to directly participate in product design and manufacturing.

In this way, high-quality customized products can be manufactured and increased traceability can be achieved. Direct feedback from manufacturing and product use to product development will shorten product innovation cycles. 2) Digital representations of products, physical assets, production operations, and business processes will enable the creation of a digital "twin" of the factory-a comprehensive virtual representation of a real factory and its processes that can be made to run in parallel to the real factory20. Models and simulations can be instantiated with product and production system data and used in the real factory decision making processes to optimize business, manufacturing, and supply chain operations and to improve product development processes. At the same time, the data coming from the real factory can be fed back to the digital factory to improve the models, knowledge bases, and simulations.

The Impact of IoT

The development and adoption of the Internet of Things (IoT) is a critical element of Smart Manufacturing 10. The technologies that will become pervasive because of the IoT-network-addressable physical and application components and standard communication protocols through which those components can communicate-will enable enterprise architectures, in general, and industrial system architectures, in particular, to move on from their traditional hierarchically and domain-specific network structure to a unified and IP-based structure10, as shown in Figure 3. This shift will enable enterprise services, such as data analytics and edge computing services, that today are typically only available at the highest levels of an enterprise to be available to serve system components in all areas of the industrial enterprise. The transition to more open network architectures, combined with Big Data and Cloud computing, will bring profound opportunities to SMS. At the same time, new security challenges are presented with billions of new smart devices being interconnected in the world of the IoT 11. The biggest security concern comes from connecting IoT devices, sensors, actuators and edge-computing units, with existing controllers, automation and manufacturing information networks, and applications. Existing OT and IT security approaches and policies will need to be adapted to embrace these new IoT security challenges. Most automation and information suppliers have established industry security services to assist clients to assess security risks and harden their manufacturing plants. Reference network architectures are available from both network equipment and automation system vendors 12. Additional challenges of integrating IOT include unreliable communications of sensors and actuators on IP networks, how to leverage IoT to boost computing power for advanced manufacturing analytics, and accessibility issues of gaining accesses to the legacy manufacturing assets.

3.3

The Impact of CPPS While the IoT deals with unique, identifiable, and internet-connected physical objects, cyber-physical systems efforts are concerned with the nature of cyber-physical coupling and the system of systems characteristics of networked and software-controlled systems. CPPS is considered the core component for German Industrie 4.0 program, where they are also referred to as I4.0 Components13. SMS are essentially composed of CPPS, which can respond intelligently to changing tasks and conditions and reconfigure themselves. CPPSs partly break the traditional automation pyramid and potentially turn the manufacturing ecosystem into a service-oriented architecture (SOA) 1516. To leverage the safety and security requirements from the OT domain, real-time and safety critical functions in legacy automation systems will remain organized in a hierarchy, and only level 2 components will be allowed to connect as services. IoT devices connected in the IT world will naturally be part of the service-oriented architecture. Figure 4 shows how the legacy hierarchical functional architecture will be transformed to a SOA-based manufacturing system architecture. As shown in Figure 5, the proposed architecture provides a completely integrated manufacturing ecosystem on a single manufacturing service bus, including both OT domain systems and IT domain systems and applications. Interactions with suppliers, customers, logistics systems are enabled through a collaborative Business intelligence (BI) service.

In the new architecture, services are classified as being one of four types: IT domain services, OT domain services, virtual domain services and management/common services. IT domain services include IoT services (e.g., smart devices, edge computing, fog computing, cloud computing, etc.), MoM services, ERP services, PLM services, and other enterprise services such as Asset Management, Energy Management, SCM, Order Management and CRM. The integration approach that will be used for IT domain services is similar to today's enterprise service bus (ESB) based approach, which is built using event-driven and standards-based message-oriented middleware in combination with message queues. In the OT domain, services involve functions provided by machines, workstations, robots, production lines, complete production cells or even products themselves. The OPC Unified Architecture (OPC UA) provides interoperability at level 2 and beyond and has the potential to provide a service-oriented architecture for OT application integration13. Data analytics services are provided through edge computing, fog computing and cloud computing in the IoT world 18. Virtual domain services are located in the digital factory, which stores the data models, function models, behavior models, and process models of a manufacturing enterprise and provides query and simulation functions for manufacturing applications. Management/common services sit at the core of the SOA architecture. They help manage the lifecycle of the SMS services, map client requests with service providers, and ensure quality of service levels met. Device management, network configuration, data management, knowledge management, and security management are provided by services in this cluster.

Based on the architecture described above, SMS can be developed and deployed that provide efficient and flexible solutions for the problems faced by the modern manufacturing enterprise. Supporting more streamlined processes, the SOA-based architecture enables customized production at mass production rates.

However, implementing the proposed architecture to create new SMS is neither simple, quick, nor cheap. It will take many years to fully realize the strength of the new architecture. The key implementation challenges include: ─ Manufacturing Service Bus capabilities -can a single manufacturing service bus meet the needs of diverse use scenarios, supporting both real-time messaging and big volume data distribution? ─ Real-time service capabilities -how should real-time services be modeled in the OT domain, how should their service interfaces be defined, and how should resource constraints be managed, i.e., when and where should resources be available to provide services? ─ IT -OT integration concerns -how can security and safety issues be handled? ─ Can high fidelity models and simulations be used in a real-time control environment without re-engineering? ─ Knowledge management concernshow can we close technology gaps in conditioning, interpreting, and contextualizing data across heterogeneous systems or situations? ─ Integration standards -how can existing standards be enhanced and new standards be developed to enable more information flow among more stakeholders.

Conclusion

In a new era of smart manufacturing, every part of a manufacturing enterprise will be digitized and connected. With the introduction of smart devices accessible as services on a network, more embedded intelligence at every level, predictive analytics, and cloud technology, the next generation of manufacturing systems will indeed get smarter. In order to realize the vision of smart manufacturing where systems respond in real time to changing demands and conditions in the factory, in the supply network, and in customer needs, the classical manufacturing system architectural paradigm based on a hierarchical control model will no longer dominate. A new paradigm based on distributed manufacturing services is starting to be adopted. This paper described a smart manufacturing ecosystem that enabled systems integration within and across three manufacturing lifecycle dimensionsproduct lifecycle, production system lifecycle, and business lifecycle. We examined how the introduction of ICT is going to impact the SMS architecture. Adoption of IoT, CPPS and cloud computing technology potentially will drive the transformation of the existing rigid hierarchical architecture style. Digital thread digital factory technology will enable the enterprise to be fully integrated with its value chain. Based on the study of the ICT architectural impact, we propose an SOA-based and model-enabled Smart Manufacturing reference architecture. The proposed reference architecture will integrate both ICT and OT systems on a single manufacturing service bus. We discussed implementation challenges that include standards for communication protocols, data model, knowledge representation, and CPPS characterization that are necessary to facilitate the adoption of Smart Manufacturing technology and the proposed architecture.

Disclaimer. Any mention of commercial products is for information only; it does not imply recommendation or endorsement by NIST.

Fig. 1 .

 1 Fig. 1. Manufacturing Ecosystem (Source: 245)

Fig. 2 .

 2 Fig. 2. Digital twin for manufacturing (Source: 9)

Fig. 3 .

 3 Fig. 3. Ubiquitously connected manufacturing systems (Source: adapted from 10)

Fig. 4 .

 4 Fig. 4. CPPS Impact on manufacturing system function architecture (Source: Adopted from 18)

Fig. 5 .

 5 Fig. 5. A Service Oriented and Model based SMS Architecture

Operational technology (OT) is hardware and software that detects or causes a change through the direct monitoring and/or control of physical devices, processes and events in the enterprise. http://www.gartner.com/it-glossary/operational-technology-ot/


Marcelo Bernardino Araújo

Rodrigo Franco Gonçalves

Selecting a Notation to Modeling Business Process: a Systematic Literature Review of Technics and Tools

Keywords: Layout, BPM, Costing Systems, Modeling, Process

There are several different notations available in the market to business process modeling. An adequate business process model tool allows the understanding regarding the several operational flows inside an organization. This article has two objectives: first, to identify and to compare alternative business process modeling notations; second, to select an adequate notation to be applied in the modeling the business process of accounting system to higher education entities. Then, a literature review was carried out, including a rigorous research in indexed database. We also tested the available tools based on BPM model. Among the studied notations the BPMN was selected since it demonstrated to be the more adequate notation for complex processes once it contains a wide variety of symbols, which are easily comprehended.

Introduction

Modeling and mapping a business helps the reduction of superfluous activities inside an organization. Both globalization and competitiveness in some sectors may lead companies to review their profit margins as well as their expenses. Optimization, i.e. the intense processes review, makes an organization more efficient, helping to increase both products and services quality and in some cases it also permits the reduction of the environmental impact [START_REF] Chompu-Inwai | A combination of Material Flow Cost Accounting and Design of Experiments Techniques in an SME: The Case of a Wood Products Manufacturing Company in Northern Thailand[END_REF].

Nowadays, there are several notations to represent a process, as for example: Business Process Management Notation (BPMN), Event-Driven Process Chain (EPC), Flowchart, Integrated Computer Aided Manufacturing DEFinition for Function Modeling (IDEF0), Unified Modeling Language -Activity (UML) and Value Stream Mapping (VSM). Choosing an notation contributes to the success of implementing an information system to manage the business [START_REF] Thiemich | An Agile BPM Project Methodology[END_REF]. But, among the diversity of available notations to represent and model a business, which one should we select?

The present article aims to identify an adequate notation to model the necessary processes to develop an accounting system applied to higher education entities, since there is a global awareness regarding the expenditures of the universities [START_REF] Araújo | Costing Systems for use in Public Universities: The Brazilian and International Context[END_REF].

In the following sections, we present a literature review of the main points to be addressed, detail the research performed, present observations regarding the response and the choice of a notation based on the literature and software tests to develop a costing system, and finally formulate the final observations that may be used to prepare a business model based on BPM.

Literature Review

Inside the organizations, several processes and procedures are created, reviewed and finalized every day. Process and procedure may be similar words, but they must be utilized correctly [START_REF] Stoneham | Innovating Business Processes for Profit: How to Run a Process Program for Business Leaders[END_REF].

While a procedure describes how a task is performed in detail and how it fits in a process, regarding how and who execute the task, i.e. a procedure details the technical requirements of a task about a process [START_REF] Stoneham | Innovating Business Processes for Profit: How to Run a Process Program for Business Leaders[END_REF], a process represents the aggregation of activities and behaviors executed by humans or machineries to achieve one or more results [START_REF][END_REF]. A process describes a sequence of activities carried out from the beginning until the end aiming to produce a result to the client, emphasizing the activity and its conduction [START_REF] Stoneham | Innovating Business Processes for Profit: How to Run a Process Program for Business Leaders[END_REF].

The Figure 1 represents the flow of a process and how its elements interact. Each process has its specific monitoring and measurement indicators necessary to its control. The formalization of a process is necessary to create either a product or a service, since it depends of inputs, several steps and procedures to fabricate a final product [START_REF][END_REF][START_REF]IIBA: A Guide to the Business Analysis Body of Knowledge (BABOK Guide), Version 2[END_REF]. A notation is defined by a set of standard, symbols and rules that determine their meaning [START_REF][END_REF]. These representations support visually the understanding of a process, either simple or complex, and it can be understand more efficiently due to an adequate notation.

Mapping and Modeling Processes

A diagrammatic representation aims to simplify the understanding about several aspects of a process, since symbols can represent several contexts. In this sense, for a better comprehension of a process, standard notations constitute a set of knowledge due to their documentation [START_REF] Bandara | Professionalizing Business Process Management: Towards a Body of Knowledge for BPM[END_REF][START_REF] Milani | Modelling Families of Business Process Variants: A Decomposition Driven Method[END_REF].

The mapping process of an organization is the knowledge and the analysis of its processes and data interconnection, and it is structured in a top-down design (from the top of the organization to the base), to a level that allows a thorough comprehension of products, services and results [START_REF] Stoneham | Innovating Business Processes for Profit: How to Run a Process Program for Business Leaders[END_REF].

It implies more precision when compared to a flow representation and it may aggregate more detail regarding, not only to the process, but also the relationship among several elements, such as stakeholders, events and results. A process map typically provides an overview about the main components of a process, but it may change from higher to lower levels of detail [START_REF][END_REF].

On the other hand, business process model is the set of activities regarding the representation of the current or a proposed process. It may provide a sideto-side perspective or a part of a primary process regarding to either support or management [START_REF][END_REF]. The process modeling is applied to represent graphically the current or a future process inside the organization [START_REF]IIBA: A Guide to the Business Analysis Body of Knowledge (BABOK Guide), Version 2[END_REF].

While the mapping process regards to a current and non-documented process, and the modeling is applied to the development of new processes and procedures.

Business Process Management

The BPM is a management discipline that integrates strategies and objectives of an organization with customer expectations and needs, by focusing on processes, end to end. This methodology encompasses strategies, objectives, culture, organizational structures, roles, policies, methods and technologies to analyze, design, implement, manage performance, process and establish governance processes [START_REF][END_REF]. It is based on two pillars:

The first one regards on the studies [START_REF] Deming | Elementary Principles of the Statistical Control of Quality: A Series of Lectures[END_REF][START_REF] Shewhart | Statistical Method from the Viewpoint of Quality Control[END_REF] about statistical control of process that originates the current quality management represented by Six-Sigma.

The second one is related to business reengineering process [START_REF] Hammer | Reengineering Work: Don't Automate[END_REF][START_REF] Hammer | Reengineering the Corporation: A Manifesto for Business Revolution[END_REF] and it has interdependent positive and negative aspects. The reengineering was initially introduced not as a continuous improvement process, but as an occasional initiative.

The application of the BPM as a management method for business process, which involve several technologies such as online tools, cloud computing, is a competitive advantage and it also supports changes as: marketing, new technologies, IT infrastructure and both clients and suppliers necessities [START_REF] Bandara | Professionalizing Business Process Management: Towards a Body of Knowledge for BPM[END_REF].

ISO, BPM CBOK and BABOK

The standardization of procedures has becoming usual mainly due to a globalized environmental [START_REF] Bandara | Professionalizing Business Process Management: Towards a Body of Knowledge for BPM[END_REF]. There is three basic tools when applied together provide a support to build a process: ISO 9000, Business Process Management Common Body of Knowledge (BPM and CBOK) and Business Analysis Body of Knowledge (BABOK). A Body of Knowledge (BOK) is a practical guide for professionals that constitute the source of knowledge for most of professional curriculums. Its content represents the basic competences required for the professionals before their accreditation [START_REF] Bandara | Professionalizing Business Process Management: Towards a Body of Knowledge for BPM[END_REF].

The International Organization for Standardization (ISO) was created in 1947 to promote normalization of products and services due to a continuous improvement ideology. Among several publications, the ISO 9000 series of standards concerns about quality management. The process approach [START_REF] Terziovski | ISO 9000 Quality System Certification and its Impact on Product and Process Innovation Performance[END_REF] allows the management of the organization due to processes interaction. Several enterprises around the world search for the ISO certification [START_REF] Terziovski | ISO 9000 Quality System Certification and its Impact on Product and Process Innovation Performance[END_REF], since the ISO 9000 conformity certification introduces credibility to the organization.

In order to avoid interference between the process and business analysts, they both have to understand the organization's necessities. The expertise of these professional can be attested by certification. The Association of Business Process Management Professionals (ABPMP) certifies the professionals due to the CBPP examination (Certified Business Process Professional) which demands a sound knowledge of the BPM CBOK procedures [START_REF][END_REF].

Moreover, two certifications are available by the International Institute of Business: CBAP (Certified Business Analysis Professional) for junior and CCBA (Certificate of Competency in Business Analysis) for senior level professionals. However, a thorough expertise of the BABOK is required [START_REF]IIBA: A Guide to the Business Analysis Body of Knowledge (BABOK Guide), Version 2[END_REF].

Methodology

We carried out a systematic literature review to select the more appropriate modeling technic to develop an accounting system, once a peer review is a typical indicator for quality, since it is based on direct expertise of the reviewers and their knowledge [START_REF] Brinn | Measuring research quality: peer review 1, citation indices 0[END_REF]. A systematic literature review process has also been shown to be an appropriate tool to manage and organize the growing number of databases for articles, allowing the identification of relevant contributions.

The selected electronic databases where the searches were conducted from January to March 2016 are showed in Table 1. A 10-year time limit for sample studies was set in order to incorporate only recent studies. The searches were conducted using the following string: "business process modeling" AND ("costing system" OR "cost accounting").

After the systematic search in the databases, we selected the studies that only satisfy the objective of choosing a modeling process method. Additionally, we tested various free source modeling tools in order to verify which one would model precisely a complex processes as the ones in public sectors, since our goal is to develop a Time-Driven Activity Based Costing to the Federal Institution of Science and Technology of São Paulo. For the process modeling we used the soft- ware Yaoqiang BPMN Editor 4.0.42 [START_REF] Geiger | BPMN 2.0 Serialization -Standard Compliance Issues and Evaluation of Modeling Tools[END_REF], and Microsoft Visio 2010 to flowchart and UML -Activity [START_REF] Fu | From engineering diagrams to engineering models: Visual recognition and applications[END_REF]. These software allowed us to model using both BPMN, UML and flowchart concepts. Moreover, the flowcharts are tools constantly applied in patents [START_REF] Ramesh | Method and system for evaluating costs of various design and maintenance approaches[END_REF]. In addition, we tested the open software named StarUML 5.0.2.1570.

The Based Knowledge Systems Incorporation (KBSI) maintains a paid version of the IDEF0 notation software, which is based on the Activity-Based Costing (ABC) method [START_REF] Tatsiopoulos | The integration of activity based costing and enterprise modeling for reengineering purposes[END_REF], however we did not tested the notation.

For EPC and VSM we applied the SmartDraw that can be used either in desktop or cloud version, which choice we based on expertise [START_REF] Davies | BPM Tool Selection: The Case of the Queensland Court of Justice[END_REF]. This software is a viable alternative for the Microsoft Visio once it is available freely and contemplates diverse notations as well as schemas, plots, flowcharts and BPMN.

Results and Discussion

The use of flowcharts is designed for users who use little information systems. The survey noted the recommendation to use BPMN in [START_REF] Thiemich | An Agile BPM Project Methodology[END_REF][START_REF] Fu | From engineering diagrams to engineering models: Visual recognition and applications[END_REF][START_REF] Trehan | Informal and formal modelling of engineering processes for design automation using knowledge based engineering[END_REF]. However, to perform the mapping and modeling processes properly, the business analyst to analyze the business requirements be careful when making the drawings, because the tasks are below the level of activities [START_REF] Stoneham | Innovating Business Processes for Profit: How to Run a Process Program for Business Leaders[END_REF].

Among the notations on the market, the most known and used were analyzed in this research. The characteristics of each are shown in Table 2.

After the systematic process of reviewing the literature and consulted and analyzed nine studies, two professional guides and a book relevant to the process of choosing the appropriate notation for modeling business processes, we reached the result shown in Figure 2.

After the analysis of the results, select the BPMN notation, because the advantages outweigh the disadvantages. Its main advantages are: ease of use, versatility, supported by other tools and mainly describe complex processes. The main drawback in using BPMN is a wide variety of symbols, therefore, the user requires a certain level of knowledge and proper use. In other notations, only IDEF0 is also capable of describing complex processes. This notation is recommended by [START_REF] Trehan | Informal and formal modelling of engineering processes for design automation using knowledge based engineering[END_REF].

Conclusions

The realized comparison of the business process notations allows the selection BPMN as the most adequate notation to map and model processes to the accounting system. This process requires a communication without noise from the Process Analyst and Business Analyst with a view to developing an IT solution.

The main advantage of BPMN is that he is able to describe complex processes. However, it has the disadvantage of a great variety of symbols, but understandable.

A costing system will be developed to the Federal Institute of Education, Science and Technology of São Paulo -IFSP based on process modeling using a BPMN notation.

Fig. 1 .

 1 Fig. 1. Representation of the elements in a process

Table 1 .

 1 Electronic databases consulted

	Name	Results
	ASCE Library	4,074
	DOAJ	2
	EBSCO host	3
	IEEE Xplore	109
	ProQuest	1
	ScienceDirect	155,94
	Scopus	7
	Web of Science	1
	Wiley Online Library 176,06

Table 2 .

 2 Notations for process modeling

	Notation	Description	Developer
	BPMN	It is useful to represent a model to different target audience.	Object Management Group (OMG)
	Flowchart	It facilitates the understanding of a process flow, however the symbols are not standardized.	American National Standards Institute (ANSI)
	EPC	It is useful to model complex sets of processes.	Institut für Wirtschaftsin-formatik Universität des Saarlandes
		It uses a systemic view highlight-
	IDEF0	ing inputs, outputs, control mech-anisms, processes control and rela-tion between lower and higher lev-	United States Air Force (USAF)
		els.
	UML Activity	It is a diagramming technique ori-ented to describe the requirements of an information system.	Object Management Group (OMG)
	Value Stream
	Mapping

It shows the efficiency of processes mapping the use of resources and time variables.

Toyota Motor

Fig. 2. Qualitative comparison of the notations

Acknowledgment

The authors would like to thank CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) and IFSP (Instituto Federal de Educação, Ciência e Tecnologia de São Paulo) for the financial support to develop this work.


Erlend Alfnes
email: erlend.alfnes@ntnu.no

Maria Kollberg Thomassen
email: maria.thomassen@sintef.no

Erik Gran
email: erik.gran@sintef.no

A Framework for Lean Flow in Turbulent High-Variety Low-Volume Manufacturing Environments

Keywords: lean manufacturing, value stream mapping, manufacturing turbulence

Value stream mapping (VSM) is a widely applied method for manufacturing systems design in repetitive and stable industries. A literature review of challenges and modified solutions for lean flow in high-variety low-volume (HV/LV) value streams is carried out. The solutions are categorized according to manufacturing turbulence level. The review shows that existing VSM solutions take their starting point in the original VSM principles and incorporate other relevant works only to a limited extent. Based upon the review, a coherent framework with revised VSM principles that that can be used to develop lean flow in HV/LV environments with medium and high turbulence levels is proposed.

Introduction

There is a need for research on extending the applicability of leanness into high variety low volume (HV/LV) environments [START_REF] Papadopoulou | Leanness: experiences from the journey to Date[END_REF]. A literature review of empirical case studies is carried out to investigate solutions of applying VSM in HV/LV environments. Many of the case studies propose modified VSM solutions to achieve a future state with lean flow in HV/LV settings, but the studies are mainly based upon the traditional VSM guidelines. They do not sufficiently build on each other to provide a more coherent set of solutions for this type of environment. The study confirms what authors such as Jina et. al [START_REF] Jina | Applying Lean Principles for High Product Variety and Low Volumes: Some Issues and Propositions[END_REF] have observed, namely that it becomes more challenging to apply VSM as the turbulence in terms of schedule changes, mix variations, volume fluctuations, and design changes increases. The purpose of this research is to identify principles for designing lean flows at different turbulence levels by reviewing modified VSM solutions for HV/LV in literature. The main contribution is a framework with revised VSM principles that that can be used to develop lean flow in HV/LV environments.

The paper is organised as follows. First, the methodological approach is discussed. Next, a review of challenges and modified solutions for VSM at different turbulence levels in HV/LV case studies is carried out. The review is used to develop a VSM framework for designing lean flow at medium and high turbulence levels. Finally, conclusions are presented together with suggestions for further work.

Methodological Considerations

The objective of the literature review is to identify relevant lean principles for designing a future state map in HV/LV manufacturing environments. The reason for this choice is that VSM is a well-known and widely used lean methodology often serving as a starting point for lean implementation as it offers a way to learning to see the process or value streams [START_REF] Rivera | Measuring The Impact of Lean Tools on the Cost-Time Investment of a Product Using Cost-Time Profiles[END_REF]. A review of relevant empirical cases in literature was carried out. The cases were identified through searches in relevant databases such as Scopus and Google Scholar. We identified 14 empirical cases that met the selection criteria; the majority of the cases (10) include a current or future state value stream map, while the additional cases (4) were selected because they propose useful solutions for how to improve value streams in an HV/LV manufacturing environment. All cases propose modified lean solutions for how to map or improve manufacturing flow.

The cases are classified into low, medium and high turbulence environments based on the turbulence factors proposed by Jina et al. [START_REF] Jina | Applying Lean Principles for High Product Variety and Low Volumes: Some Issues and Propositions[END_REF]. The VSM design principles proposed by Rother and Shook [START_REF] Rother | Learning to See: Value Stream Mapping to Add Value and Eliminate Muda[END_REF] are used as a reference framework to structure the case studies. The modified VSM principles that are proposed to meet major challenges are classified according to turbulence level.

3

Literature Review

The frame of reference is presented in this section. It includes general VSM design principles for flow manufacturing, HV/LV manufacturing and turbulence levels and a categorization of modified solutions for low, medium and high turbulence environments.

General VSM Design Principles for Flow Manufacturing

As part of the VSM methodology, Rother and Shook [START_REF] Rother | Learning to See: Value Stream Mapping to Add Value and Eliminate Muda[END_REF] defines a set of general design principles for creating flow. The principles represent rules that are to be followed and essential characteristics of a lean flow system; ─ VSM is carried out for a specific product family. A family is a group of products that passes through similar processing steps and over common equipment in down stream processes. ─ The production pace should be synchronized to match the pace of sales, i.e. to produce to takt time, where takt time refers to the "available production time"/"customer demand".

─ Continuous flow should be developed where it is possible, i.e. producing one piece at the time, with each item passed immediately from one process step to the next without stagnation. ─ A pull system should be used to control production where continuous flow is not possible. In supermarket pull systems, Kanban trigger replenishment of what is used. If it is not practical to keep all parts in a supermarket, FIFO lanes, CONWIP, or sequenced pull might be an alternative. ─ The customer schedule should be sent to a single production process. The pacemaker is the only scheduling point, and sets the pace for all upstream processes. Flow (no pull) is required downstream of the pacemaker, and it is frequently the most downstream process in the value stream. With custom products and job shops, the pacemaker often needs to be further upstream. ─ The production mix and volume should be levelled. This means that the production of different products should be distributed evenly over time at the pacemaker process. Hereby a daily production rate is established that is equal to the average expected demand and to release and withdraw small consistent increments of work (pitch) at the pacemaker process.

HV/LV and Turbulence

HV/LV manufacturing environments include one-of-a-kind as well as small batch manufacturing environments. Manufacturing is usually make-to-order or engineer-to-order, and is normally performed in job shops [START_REF] Portioli-Staudacher | A Lean-Based ORR System for Non-repetitive Manufacturing[END_REF]. A main challenge for lean implementation in HV/LV is that they are experiencing more variability [START_REF] Hines | Learning to Evolve: A Review of Contemporary Lean Thinking[END_REF]. High levels of unpredictability and instability in dynamic environments make it difficult for lean operations to synchronise production processes and reduce inventory, and undermines the effectiveness of lean operations. Jina et al. [START_REF] Jina | Applying Lean Principles for High Product Variety and Low Volumes: Some Issues and Propositions[END_REF] proposes four turbulence factors that create unpredictable and sub-optimal behaviour in manufacturing systems:

─ Changes in scheduleirregular demand creates many schedule changes close to delivery due date. ─ Changes in product mixmarked differences in product mix between one period and the next creates variations in workloads, especially when there is significantly different cycle time for each item. ─ Volume changesaggregate volume changes between periods over time. ─ Design changesthe degree of design changes and amount of engineering work involved, and the frequency of design changes creates uncertainty and rework in manufacturing.

According to Jina et al. [START_REF] Jina | Applying Lean Principles for High Product Variety and Low Volumes: Some Issues and Propositions[END_REF] these four types of turbulence will have a far greater impact on companies with lower manufacturing volumes than the typical lean manufacturers because the aggregated volumes in typical lean manufacturers have a beneficial dampening effect. The turbulence in HV/LV manufacturing will vary from medium to high levels. Many HV/LV manufacturers have a dominant flow in their job shops [START_REF] Portioli-Staudacher | A Lean-Based ORR System for Non-repetitive Manufacturing[END_REF], and might experience less turbulence compared to the most volatile cases. Most HV/LV manufacturing systems do not only include jobbing, but also batch and flow manufacturing processes for components with higher volumes [START_REF] Hicks | A Typology of UK Engineer-to-order Companies[END_REF]. HV/LV manufacturers with a share of flow manufacturing processes will probably experience reduced levels of turbulence. Product features will have a large impact on turbulence. HV/LV products will vary in innovativeness and complexity [START_REF] Cigolini | When ETO Companies Design the Supply Chain During New Product Development Process[END_REF], and can range from purely customised designs to standard designs that are kept "in stock" [START_REF] Wikner | Integrating Production and Engineering Perspectives on the Customer Order Decoupling Point[END_REF]. Standard MTO designs, with moderate complexity and innovation, can reduce turbulence to a medium level.

Modified VSM Design Solutions

The review of relevant case studies highlights several challenges of applying general VSM principles related to level of turbulence. In low turbulence environments, most principles seem to be easily applicable, including product family, takt time, continuous flow, pacemaker and levelling due to low variability. More challenges occur in the higher levels of turbulence.

For instance, determining a product family is a major challenge when products are produced in low volumes, high mix, are combined with customization, include multiple branches that merges and there are limited similarities between products or projects [START_REF] Lander | The Toyota Production System and Art: Making Highly Customized and Creative Products the Toyota Way[END_REF][START_REF] Duggan | Creating Mixed Model Value Streams: Practical Lean Techniques for Building to Demand[END_REF][START_REF] Stamm | Value Stream Mapping (VSM) in a Manufacture-To-Order Small and Medium Enterprise[END_REF][START_REF] Mcdonald | Utilising Simulation to Enhance Value Stream Mapping: A Manufacturing Case Application[END_REF]. Due to high variety and low volumes and constantly changing projects, the traditional definition of product families may not be applicable [START_REF] Matt | Adaptation of the Value Stream Mapping Approach to the Design of Lean Engineer-To-Order Production Systems: A Case Study[END_REF][START_REF] Matt | Implementing Lean In Engineer-To-Order Manufacturing: Experiences from[END_REF]. Moreover, the production of a high mix of custom and standard products, that require a lot of different parts and materials, may impose major challenges for synchronizing flows [START_REF] Mcdonald | Utilising Simulation to Enhance Value Stream Mapping: A Manufacturing Case Application[END_REF][START_REF] Horbal | Implementing lean manufacturing in high-mix production environment[END_REF]. Also, in situations where customer influences products that are in production, there is limited applicability of Kanban and supermarkets [START_REF] Matt | Implementing Lean In Engineer-To-Order Manufacturing: Experiences from[END_REF].

In order to deal with major challenges and design a lean future state, several of the investigated case studies propose modified VSM solutions. These are listed in Table 1. Make families of similar projects [START_REF] Matt | Adaptation of the Value Stream Mapping Approach to the Design of Lean Engineer-To-Order Production Systems: A Case Study[END_REF] Separate repetitive and handicraft projects in two families [START_REF] Matt | Implementing Lean In Engineer-To-Order Manufacturing: Experiences from[END_REF] Takt time Medium Use takt rate (pcs/day) when variation is high [START_REF] Lander | The Toyota Production System and Art: Making Highly Customized and Creative Products the Toyota Way[END_REF] Establish a set of takt modes to meet demand fluctuations [START_REF] Duggan | Creating Mixed Model Value Streams: Practical Lean Techniques for Building to Demand[END_REF] Apply the takt time concept to the production unit as a whole and not to each individual operation [

19] High

A takt time is possible to implement for runners parts with high, stable demand [START_REF] Matt | Implementing Lean In Engineer-To-Order Manufacturing: Experiences from[END_REF]

Continuous flow

Low

Synchronisation between critical path and other branches through supermarkets and pull [START_REF] Braglia | A New Value Stream Mapping Approach For Complex Production Systems[END_REF] Medium Customised and standard products are produced in the same value stream [START_REF] Lander | The Toyota Production System and Art: Making Highly Customized and Creative Products the Toyota Way[END_REF][START_REF] Duggan | Creating Mixed Model Value Streams: Practical Lean Techniques for Building to Demand[END_REF][START_REF] Mcdonald | Utilising Simulation to Enhance Value Stream Mapping: A Manufacturing Case Application[END_REF]] Customised products are only released for production when all material and engineering information is available [START_REF] Mcdonald | Utilising Simulation to Enhance Value Stream Mapping: A Manufacturing Case Application[END_REF] Connect resources that are shared by several families into the flow through sequenced FIFO [START_REF] Duggan | Creating Mixed Model Value Streams: Practical Lean Techniques for Building to Demand[END_REF] High Flow runners parts in focused cells with processes that are temporarily dedicated for a given duration, produce repeaters and strangers in less frequent batches within cells, in flexible job shops, or contract out to suppliers [START_REF] Jina | Applying Lean Principles for High Product Variety and Low Volumes: Some Issues and Propositions[END_REF] Assemble runners in lots and intersperse them with repeaters and strangers [2] Pull system Medium Customised products are produced by customer order (directly to shipping) and standard products are produced to a finished goods super market [START_REF] Mcdonald | Utilising Simulation to Enhance Value Stream Mapping: A Manufacturing Case Application[END_REF] CONWIP is applied on the production unit as a whole [START_REF] Mcdonald | Utilising Simulation to Enhance Value Stream Mapping: A Manufacturing Case Application[END_REF][START_REF] Bokhorst | Lean Production Control At A High-Variety[END_REF] Runners and medium volume repeaters are pulled by Kanban, low volume repeaters and strangers are controlled by sequential FIFO [START_REF] Horbal | Implementing lean manufacturing in high-mix production environment[END_REF]

High

Fast MRP with ability to monitor schedule changes and their impact on lower level demand. [START_REF] Jina | Applying Lean Principles for High Product Variety and Low Volumes: Some Issues and Propositions[END_REF] Use Kanban for parts with reasonably stable demand [START_REF] Jina | Applying Lean Principles for High Product Variety and Low Volumes: Some Issues and Propositions[END_REF][START_REF] Matt | Implementing Lean In Engineer-To-Order Manufacturing: Experiences from[END_REF] A central supermarket and picking zone are established to provide parts to the assembly department [START_REF] Matt | Implementing Lean In Engineer-To-Order Manufacturing: Experiences from[END_REF] Pacemaker Low A pacemaker is implemented at the bottleneck in the value stream [START_REF] Serrano | Pacemaker, Bottleneck and Order Decoupling Point in Lean Production Systems[END_REF] Medium The whole production unit is considered as a pacemaker [START_REF] Lander | The Toyota Production System and Art: Making Highly Customized and Creative Products the Toyota Way[END_REF] A pacemaker is located after the CODP [START_REF] Mcdonald | Utilising Simulation to Enhance Value Stream Mapping: A Manufacturing Case Application[END_REF] or at the bottleneck [START_REF] Stamm | Value Stream Mapping (VSM) in a Manufacture-To-Order Small and Medium Enterprise[END_REF] Levelling Low Work load and product mix is determined by the capacity and minimum lot size at the bottleneck [START_REF] Serrano | Pacemaker, Bottleneck and Order Decoupling Point in Lean Production Systems[END_REF] Medium Daily production target defined by takt rate; mix levelling at family level only; buffering of runners as finished goods to deal with demand variability; variable lead-times quoted to customers provides additional buffering [START_REF] Lander | The Toyota Production System and Art: Making Highly Customized and Creative Products the Toyota Way[END_REF]

High

Order sequencing with lead time and work content smoothing objectives [START_REF] Jina | Applying Lean Principles for High Product Variety and Low Volumes: Some Issues and Propositions[END_REF] Outsource to external suppliers if needed. Split customer orders into smaller production orders, release equal time increments of work [START_REF] Matt | Adaptation of the Value Stream Mapping Approach to the Design of Lean Engineer-To-Order Production Systems: A Case Study[END_REF] Customer orders are split into smaller production orders (pitches) and scheduled to satisfy just-in-time delivery to the building site [START_REF] Matt | Implementing Lean In Engineer-To-Order Manufacturing: Experiences from[END_REF] The few VSM case studies that propose future state maps in high turbulence environments seem to select "sheltered islands" in the manufacturing system that are separated from more unstable and varying value streams. Such units are typically producing components (such as motors or valves) that are used across many projects, and have sufficient volumes to utilise more flow-oriented manufacturing processes. They tend to have a dominant flow and a turbulence levels that make VSM more applicable. In high turbulence environments where no dominant flow or less turbulent production units can be identified, the applicability of VSM is limited.

VSM design principles, either in a standard or modified form, becomes more applicable as turbulence in schedule, mix, volume, and design decreases. The level of turbulence is partly determined by the product features that are offered. Product features is a strategic decisions, and there can be very good reasons, such as high margins, to position the offerings in the purely customised segment. In such situations, the manufacturer will experience high turbulence and VSM becomes less applicable. The level of turbulence is also determined by the ways the order fulfilment process has been arranged and managed. By predefining the product solution space and automate some of the engineering design processes associated with the specification of a product, turbulence is reduced.

A Flow Design Framework for HV/LV Manufacturing

Based upon the review of modified VSM solutions identified in literature, a framework for HV/LV manufacturing settings is proposed, see Table 2. The review reveals that higher level of turbulence in HV/LV manufacturing makes the general lean principles more difficult to apply. The framework includes suggestions for both high and medium turbulence settings, since HV/LV manufacturing companies may represent both turbulence levels.

Conclusion

This paper analyses cases where VSM is applied in manufacturing environments that are relevant for HV/LV. The cases are classified according to turbulence level. A framework for flow design in HV/LV manufacturing is proposed. The review shows that the standard VSM design principles are easily applicable in low turbulence settings, and that modified versions of VSM are less problematic in medium turbulence environments compared to high turbulence environments. The major contribution includes an overview of existing modified VSM design principles for HV/LV settings. Detailed insights to modified solutions for different turbulence levels are provided. The framework of modified VSM design principles may serve as a starting point for the development of practical guidelines in HV/LV environments. Manufacturers, especially with medium turbulence, may use the framework to establish flow. Manufacturers in highly turbulent environments should seek to reduce the level of turbulence to ensure efficient application of the modified VSM design principles.

The framework should be further refined by testing modified design principles in one or several case companies representing environments of different turbulence levels.

Table 1 .

 1 Modified solutions of investigated cases for low, medium and high turbulence levels

	Principle	Turb.	Proposed solutions
		level
	Product	Low	Identify and map critical path including insertion points for other
	family		branches and shared resources [17]
		Medium Make families of several products that have moderate differences in
			routings and cycle times [10, 11, 13, 16, 18, 19]
		High

Table 2 .

 2 A flow design framework for HV/LV environments Produce customised and standard products in the same value stream and control the flow through FIFO lanes. Only release customised products for production when all material and engineering information is available. Connect shared resources and other branches into the flow through sequenced FIFO. If turbulence is high, schedule changes and design changes happens, and numerous routings and cycle times are possible. Keep all products in the same value stream, or establish value streams based on broad project families in order create a "quasi-continuous" flow and a reduction of disturbances. If no takt is feasible, control the flow through CONWIP. a backlog of productions orders, and release them in a takt to control the pace of the value stream. With custom products and job shops, the pacemaker often needs to be upstream. Locate a pacemaker after the CODP and/or at the bottleneck. If turbulence is high, no single pacemaker can be identified. Use the whole value stream as a pacemaker. Levelling Define daily production target by takt time, level mix at family level only, and use buffer of runners as finished goods to deal with demand variability. Use variable lead-times quoted to customers provides additional buffering. If turbulence is high, try to cope with schedule changes, design changes, and demand fluctuations trough order sequencing with lead time and work content smoothing objectives. Ramp up capacity if needed. Extreme load peaks are outsourced to external suppliers.

	Category	Design principles
	Product family Make a family of several products with similar routings and cycle times. Map
		the critical path in the product structure, but also include insertion points for
		other branches and for shared resources
		If turbulence is high, routings and cycle time can vary wildly. Make broad fam-
		ilies of projects with some similarities in demand, geometry, level of custom-
		isation etc.
	Takt time	Apply takt time as = effective working time / sum of demand of all products in
		the family during that time. Establish a set of takt modes to meet demand
		fluctuations.
		If turbulence is high, takt time does not make sense to control pace in daily pro-
		duction. Use a takt rate (pcs/day or pcs/week) that is revised monthly.
	Continuous
	flow
	Pull system	Produce customised products to customer order (directly to shipping) and pull
		standard products to a finished goods supermarket. Parts that are runners and
		medium volume repeaters are pulled into the main flow by Kanban, control
		low volume repeaters and strangers by sequential FIFO lanes.

Acknowledgements. This research is supported by the Research Council of Norway through the research projects EFFEKT and Manufacturing Network 4.0.