## 3 A SOA-Based Engineering Process Model
### The Eight Arrowhead Engineering Process Phases  
We designed the Arrowhead-EP (Figure 3) as a flexible solution to support the intertwined EPs of different use cases that characterise the industry domain. The eight phases composing the Arrowhead-EP are described as follows:  
1. The **Requirements** elicitation phase consists of identifying the system requirements from users, customers, and other stakeholders. The output of this phase is typically the list of system requirements. 2. The **Functional design** phase consists of adopting the _functional design_ paradigm to simplify the system design. A functional design assures that each modular part of the system has a precise role and performs that role correctly together with the other parts. Functionally designed modules tend to have low coupling. The output of this phase is typically a model or an architecture. Depending on the type of project, the output of this phase can also be a cyber-physical system model and/or a computer simulation. 3. The **Procurement and Engineering** phases proceed in parallel and are continuously interacting. The _procurement_ phase consists of finding and agreeing to terms and acquiring the goods, services, or works required to engineer the system and construct or manufacture it from an external source. This phase is used to ensure that the buyer receives goods, services, or works at the best possible price when aspects, such as  
Figure 3: The Arrowhead Engineering Process and Engineering Process Units defined in the ontology. quality, quantity, time, and location, are compared. The _Engineering_ phase, in turn, includes the design, development, and testing of the system, prototype generation, and after some iterations, the final version of the system (that will be _Deployed and Commissioned_). Considering the concept of feedback, engineering teams are also responsible for understanding the causes of the malfunctioning identified during the _Operation/Maintenance_ phases and implementing the improvements determined during the _Evolution_ phase. 4. The **Deployment and Commissioning** are sequential phases intended to prepare the system for operation. The _deployment_ consists of the installation and integration of the system in a laboratory for testing and debugging purposes or in the final operative environment and includes the preliminary verification and validation of the system. _Commissioning_ is the process of ensuring that the system is designed, installed, tested, operated, and maintained according to the operational requirements of the owner or the final client. _Commissioning_ may be applied to new projects but also to existing systems subject to renovation, updates (e.g., for maintenance purposes), or expansion (see _Evolution_ phase). 5. The **Operations and Management** consists of operating and managing the system according to the operational specification and requirements of the owner or the final client. From a temporal perspective, this is generally the longest phase in the system life cycle. In this phase, the system is also monitored remotely to acquire information about its behaviours during operations. This information is aggregated and dispatched to the _Maintenance_ and _Evolution_ phases but, if needed, also to other stakeholders in the system value chain for further analysis and activities, depending on their role. 6. The **Maintenance, Commissioning, and Recycling** phase consists of identifying and establishing the requirements and tasks to be accomplished to achieve, restore, and maintain the operational capability of the system across the entire life cycle. The _Maintenance_ process must be executed concurrently with the operations process. _Maintenance_ addresses bug fixes and minor enhancements, as well as minor adaptations to the standards, new features, software updates, and troubleshooting. In contrast, considerable changes in the system are identified and planned in the _Evolution_ phase.