2.1 Factory of the Future
Particularly in today's global markets, constant changes in requirements are inevitable, therefore, modern factory planning must react with sustainable and long-term concepts. This in turn, increases the requirements in the planning process [4]. The development of technologies in the area of Industry 4.0 has led to the emergence of the concept of a digital FoF as a system of integrated technological solutions that provide the shortest time to design and manufacturers globally competitive next-generation products. It is defined as a system of integrated engineering domains such as production infrastructure, production processes and the product [2]. In the FoF, the Digital Shadow technology refers to the production process and the product, while Building Information Modelling provides digitalization of the production infrastructure [5, 6]. The FoF supports the entire production lifecycle from the development and planning stage and ends with the creation of a Digital Shadow [4], a BIM model and the concept of a smart and virtual factory [7]. Thereby the virtual factory stands for the digital representation of a real production site and a smart factory describes a self-organizing production environment. According to current studies [1, 2], the digital Factory of the Future is a promising concept for the decision support in factory planning.
2.1.1 Potentials of the integration of BIM and DS
BIM models contain detailed information about three-dimensional geometry of the FoF facilities, the appropriate rich semantics of structure elements and all engineering networks in buildings, as well as detailed information on the function of the infrastructure supporting the production process [8]. The Digital Shadow represents the entire production of the FoF and its processes, including its products and peripherals [4, 7]. The scientific community predicts cross-sectorally that the integration of BIM and DS technologies are inevitable for the future-oriented development of the FoF. According to [1, 10], these technologies are intended for the digital representation of different objects but simultaneously related to parts of the same physical asset. Nevertheless, they are developed in parallel and often without interconnection, despite a close physical connection between both domains [5, 12]. Currently, the digital technologies of BIM and DS are hardly even associated in terms of the FoF, caused by the fact that their data is very heterogeneous. At present, the lack of an adequate concept of integration of DS technology with BIM technologies significantly slows down the progress in research and development for digital, smart and virtual factories. Thus, developing a valid concept for integrating said technologies creates enormous added value in the planning and management of factories across industries.
The advantages of digitalization of the entire production environment refer to the entire life cycle of factories and their products equally, since essential long-term decisions and adjustments can be made with higher planning quality and reliability based on the data obtained from the Digital Shadow and the BIM of the FoF (e.g. the optimization of the trajectories of transportation vehicles and workers [9]).
Therefore, the issue regarding the role and place of the concept of the FoF in the formation of production assets is actively discussed by the scientific community and businesses, but it has not yet been sufficiently developed. Furthermore, the method of the Life Cycle Assessment based on these technologies can make planning even more sustainable by simplifying or anticipating quick adaptations to changing conditions through long-term oriented planning. Based on the existing potentials and the insights that can be generated, the result of the combination and convergence of BIM and DS technologies can be considered as a Digital Asset of a company, providing economic benefits (see Chap. 2.1.2).
The imbalance between the high demand for collaborative and holistic conception for the integration of BIM and DS technologies on the one hand and one-sided solution approaches on the other hand shows the urgency to investigate different possibilities for the integration of the two mentioned technologies. Related to this is the need to develop appropriate principles and methods and to evaluate the effectiveness of the imbedding of these technologies in the context of the FoF. This is precisely where this contribution comes in. It is also urgent to identify the potential of the FoF in an actual case. Therefore, in order to realize Factory of the Future technologies, the following features are required:
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adequate digital representation of physical construction objects;
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adequate digital representation of physical production items;
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bidirectional data flow between physical and digital world;
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ability to be integrated into the factory Product Lifecycle Management (PLM) system;
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ability to be used in factory Life Cycle Assessment (LCA);
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ability to generate value and reduction of operational expenditures.
BIM and DS technologies have such features and therefore should be the core technologies in the Factory of the Future and have to be integrated in order to accumulate convergence between applied techologies.
2.1.2 Added value of the integration: The idea of Digital Assets
According to economic theory, an asset is any resource owned or controlled by a business or an economic entity. This is anything (tangible or intangible) that can be utilized to produce value and that is held by an economic entity and that could produce positive economic value [13]. Therefore, we use the term Digital Asset in order to describe a digital entity (resource) which belongs (or partly belongs) to the owner and can potentially generate economic value. BIM, DS and their convergence [14] are actual examples of Digital Assets due to the fact that they are able to reduce operational costs [15–16].
Minimization of time and errors during changeover of production factors, which provide the main advantages of the proposed approach, must be taken into account when developing and operating the FoF. In our opinion, the management of factors should be ensured through the integration of BIM and DS technologies, synchronized in data transfer formats and in time. Integration of BIM and DS technologies within the framework of a single information model FoF will allow to combine all the knowledge and competencies that are formed through the entire life cycle: design, creation, validation and operation. Thus, the FoF information model becomes a Digital Asset that unites the knowledge base about an object. The Digital Asset, on the one hand, must have integrity, which means to be an adequate representation of a single physical object - FoF. On the other hand, the Digital Asset must have divisibility, which means that it must satisfy the requirement of sharing information between participants in the life cycle of an object. Integration of BIM and DS is a prerequisite for digital activation of the FoF in the form of an information model as a knowledge base accumulated by designers, builders and technologists. The integrity of such faculties implies constant synchronization of information about the actual parameters of FoF objects with their digital representations, as a result of which digital models are trained and the technical parameters of FoF are predicted throughout their life cycle.Without a doubt, the value of a Digital Asset can be obtained through the separate implementation of BIM and DS technologies. In addition to this fact, their integration is multiplicative, which means that the holistic integration of these technologies also provides additional value for FoF. This happens due to the fact that according to the degree of their consistency that determines how quickly and with what precision in the organization, adjustments and operational processes will be eliminated. Due to the fact that digitization is a modern direction in science, there are no correct and widely spread methodologies to measure added value of digital items from an economic point of view. Therefore, a coherent methodology of estimating the value of the FoF as a Digital Asset needs to be developed.
Overall, we can consider the FoF model as a virtual asset with some value advantages. The estimation of this value is not trivial; it includes the estimation of both the values of BIM and DS and the added value of their integration. The Digital Asset has to be developed as a tool for this estimation to verify the costs of digital modeling and connecting domains.
2.2 Semantic Web as integration technology
Knowledge-based approaches have generally proved to be particularly suitable for modelling of complex production networks. They support explicit representation of knowledge in a relevant domain and the development of this knowledge through reasoning mechanisms, in order to provide effective services for cross-domain collaboration [17]. Semantic Web [18] extends the principles of knowledge-based approaches to scenarios on the Web by focusing methods for data integration and intelligent reasoning with large data amounts [19, 20]. The conceptualisation of the Semantic Web is enabled by ontologies, which are used for the definition of data semantics in a machine-readable way. Ontologies represent a set of domain data concepts, its taxonomy, interrelations, and the rules that govern such concepts [21, 22].
In the field of production engineering, the Semantic Web has received great attention for its ability to make interactions within Digital Shadows more flexible and automated. Several upper ontologies for manufacturing, such as DOLCE [23], SUMO [24] or MASON [25] were developed. Moreover, Semantic Web technologies have also been discussed in several research projects in infrastructure and building science. [26] presents a semantic reasoning framework for the integration of BIM data sources, which allow to detect errors of included 3D models. In [27], querying different BIM sources by using linked building data of different ontologies has been realized successfully. Despite promising results of using ontologies for semantic interoperability in both domains, the possibility of their connection has still not got proper attention. Open data formats, such as the Industry Foundation Classes (IFC) specification, have been developed to describe and exchange information within the architecture, engineering and construction industry [28]. However, the lack of semantic information hinders their application. In industry, initiatives such as the Open Services for Lifecycle Collaboration (OSLC) [29] try to establish the application of ontologies in engineering tools. Nevertheless, a comprehensive methodology of connecting BIM and DS domains based on Semantic Web technologies has not been developed yet.
2.2.1 Ontology-based Data Access (OBDA)
The main idea of the Ontology-Based Data Access (OBDA) approach is to use ontologies as high-level schema for governing multiple sources of diverse data, allowing users to directly access data via all-accessible RDF-Format. The access is enabled by a three-level architecture, consisting of the ontology, the mapping and the data source layers. An OBDA system translates user queries from a familiar vocabulary of the ontology into the vocabulary of the underlying data sources and then delegates the actual query evaluation to a suitable query answering system of the data source [30].
In the Cluster of Excellence ”Internet of Production” of the RWTH Aachen University, ontologies are supposed to be an enabler for a new level of cross-domain collaboration along the entire value chain of production technology [31]. Application examples reach from an implementation of the OBDA approach in laser processing, up to the creation of a cross-disciplinary catalogue with an overview of the data generated in the project [32]. Moreover, the OBDA approach has been approved to have a high potential for applications, in which data sources are multiple, diverse and not organized in a uniform and coherent way [32–34]. The concept of BIM and DS integration meets these application criteria. These technologies are very heterogeneous and include data ranging from 3D modeling of assets up to machine data streams from the shopfloor. With the OBDA-approach, an integration and management of the BIM and DS domains can be achieved.
2.3 Decision support in factory planning
Decision support in factory planning currently bases on static data only and requirements, neglecting dynamic process data of DS and the life cycle assessment (LCA) of the factory. As a result, only a short planning horizon of factory planning projects is possible, covering a small interval of the entire factory lifecycle. However, in today’s turbulent and volatile market it is no longer sufficient to limit the planning and design process of dynamic and highly complex factories to short-term periods of time. Rather, the long-term perspective must be taken into account already in the early phases of factory planning.
2.3.1 LCA
Life Cycle Assessment, also called Life Cycle Analysis, is a method originally used to evaluate the environmental impact of a product over its life cycle. It includes the extraction and processing of raw materials, manufacturing, distribution, use, recycling, and final disposal [35]. At each level of the life cycle, all energy and material flows exchanged with the natural environment are identified to examine the impacts in ecological impact categories. Thus LCA can also be used as an ecological assessment method for the effects of production processes, infrastructure and resources of a factory over its entire life cycle.
Although the life cycle analysis is ISO-standardized and established in many industry areas, it is currently used as an evaluation tool for existing products and production processes only. While various other software and tools of the FoF are already fully utilized in factory planning, LCA is currently rarely used and if so, it is not integrated into the planning process [36]. The reason for this lies in the high complexity of the currently used databases as well as in the lack of knowledge regarding suitable interfaces for integrating the LCA data into the planning process. This causes a major research gap, since the methodology could be further developed from a pure evaluation tool to a design tool for sustainable factories. Especially since the potential of LCA is already apparent in the context of factory planning and only needs to be utilized for this area of application.
It is a fact that in today's factory planning, decisions have to be made whose effects will last for many years. However, increasing dynamics and volatility in the environment of manufacturing companies, considering the longest possible period of time representing a major difficulty for the early planning phases of factories, as various variables and needs for long-term adjustments are still unclear up to this point. However, only the interaction of LCA, BIM and DS technologies is able to make reliable predictions about possible scenarios and their impacts during the life cycle of a factory. For this purpose, the LCA method requires an enormous amount of highly detailed digital data, which can be provided in the required quality and reliability by integrating BIM and DS technologies. In this context, the compatibility of the three technologies must be clarified.
2.4 Problem summary
The Factory of the Future needs to be based on the integration of DS and BIM. This integration is a basic requirement, as factory planning addresses the factory building and the design of factory equipment. The problem is that only when both planning areas are considered in an integrated manner, a meaningful, complete data source can be generated and an overall optimum of planning be achieved. Therefore, the data and planning-related integration of BIM and Digital Shadows need to be performed in terms of the FoF. This requires the development of an appropriate methodology that solves the fundamental problem of creating interoperability between project-specific DS and BIM models and the respective planning processes based on a matrix of requirements and constraints. The methodology must include a classification for the information models of BIM and DS in order to be able to define the requirements for the objects to be integrated. In addition, to achieve this goal, it is necessary to conceptualize the term Digital Asset and consider the evaluation of the added value of the integration of BIM and DS.
Moreover, the integration of DS and BIM technologies in the Factory of the Future requires a new level of cross-domain collaboration along the entire factory lifecycle. For this purpose, semantically adequate and context-aware data needs to be made available on an appropriate level of granularity, so that production engineering and planning models can be integrated into data driven optimization processes [37]. An integration network must span diverse domains of construction and production engineering models. Moreover, comprehensive networking of human and non-human production systems is crucial. Therefore, the integration network must be modular with respect to languages and tools and must make process information accessible and readable for all process entities, regardless of their origin and domain.