## 3 A SOA-Based Engineering Process Model
### The Arrowhead-EP Model  
To meet the flexibility and automation levels required by Industry 4.0, the usage of IoT-based and SoS-based solutions represents an adequate approach to support the digitalisation of modern manufacturing facilities. However, technology is not enough, because even the engineering process must ensure the same levels of flexibility and automation across all phases of the product life cycle. For this reason, the rigidity of today's approaches to automation, based on standards, such as the ISA-95 architecture [56], represents a substantial limiting factor. More recent standards, such as RAMI 4.0 and IIRA, attempt to address the issue of engineering process flexibility but do not support it when moving from pure automation to the automation of the digitalisation process. RAMI 4.0, for example, proposes managing this complexity by addressing it from three different perspectives (three dimensions of the problem space): (i) business, (ii) systems and components, and (iii) life cycles. The RAMI 4.0 reference model does not elaborate on how the parts within this convoluted solution space are interconnected and interact. It does not consider different stakeholders, who sometimes might have conflicting interests. In other words, it is not clear how the new generation standards can implement a data-driven architecture (Digital Thread) that links together information generated from across the product life cycle [28]. In this work, we decompose and remodel the engineering process with the aim of introducing a service-oriented solution intended to efficiently, flexibly, and effectively manage the three assets addressed by RAMI 4.0 and extend the model with the capability to support some concepts of collaborative product development. We develop a model to enable the analysis of all the phases in a multistakeholder engineering process. Focusing on a single stakeholder, the EP is partitioned into eight engineering process phases (EPPs), as shown in Figure 3. Tool chains and tools developed for building the use case are associated with the specific EPPs where they are used. The ontology of a specific EP also reveals how EPPs, tool-chains, and tools interact, even between different stakeholders. With this approach, for example, it is possible to assign a CAD tool to the design phase of the EP of a car manufacturer, link it to the engineering phase of the same EP, and connect it to the requirement phase of the EP of a supplier that provides the specification of the components that are mounted in the car. We identify six main objectives that the EP should have to satisfy the needs of Industry 4.0 in the life cycle management of smart production:  
1. The extension from design time to run time engineering, i.e., the life cycle continuous engineering. 2. The shift from single stakeholders to multiple stakeholders integrated EP automation and digitalisation. 3. The capability to handle a substantially increased number of I/O due to much more fine-grained automation. 4. The inclusion of digital education and training activities as an integral part of EP. 5. The reduction of engineering costs obtained through the full digitalisation and management of the system life cycle. 6. The adoption of a service-oriented framework, native tool-chains/tools and legacy tools adapters to simplify, encourage, and promote the use of the new Arrowhead-EP model. As the first step to reach these objectives, we propose extending the current automation engineering standard IEC 81346 [34] by addressing the common challenges of modern industry and supporting the sustainability of the engineering and manufacturing processes. IEC 81346 does not consider EP phases that are key for Industry 4.0 and does not support feedback between phase and phase reiteration. To avoid these limitations and solve the issues identified in the gap analysis proposed in [55], we add three supplementary phases to the five already present in the original IEC 81346-based EP (Figure 2), and we introduce the possibility of reiterating phases and managing feedback.