## 3 A SOA-Based Engineering Process Model
### The VCEP-Map Ontology  
The Arrowhead-EP model is further extended with the _Value Chain Engineering Process map (VCEP-map)_ to better describe and visualise the entire value chain associated with the system. The VCEP map allows us to highlight the value chain dynamics, the relations between the engineering phases, the tool chains and tools, the relations and synergies between the stakeholders, and the components of the system. The VCEP map contains complementary information that, when combined with the Arrowhead-EP ontology, provides a 360-degree view of the use case and the associated value chain across the entire system life cycle. A VCEP map is structured in a tabular format, where each stakeholder is identified by a specific colour and a unique ID. The columns represent the Arrowhead-EP phases (i.e., the system life cycle), and the rows contain a specific aspect of the value chain. Figure 6 illustrates an example of the VCEP map associated with the multistakeholder Arrowhead-EP represented in Figure 4. The example describes seven different aspects of the value chain. In the first row, we have the eight engineering phases of the Arrowhead-EP model grouped in one line (i.e., all the edges connecting the different phases are hidden, and the phases from the different stakeholders are grouped). Then, from the second row on, we represent value chain information useful for characterising and evaluating the complexity of the different activities implemented during the life cycle of the developed system. In the second row, labelled _Value and Supply-Chain_, we map the stakeholders on the Arrowhead-EPPs where they are involved. In the third row, using the stakeholders' colours, we map the _Tool-Chains_ (graphically represented with bars having the same  
Figure 5: The web tool developed to represent multilayer Arrowhead-EPs of several stakeholders involved in the system life cycle. We focus on part of the Arrowhead-EP schema of Figure 4, highlighting the interaction between StkH1 and StkH2. colours of the StkH bars) adopted by each stakeholder on the Arrowhead-EPPs, and in the next row, the _Tool-Chains Automation Level_ is expressed as a percentage. Then, in row _System Components Tool-Chains view_, we show where each component of the system is mapped on the Arrowhead-EPPs and on the tool-chains that are used during its life cycle. In the following row named the _System Components StkH view_, we aggregate information provided in the _System Components Tool-Chains view_ for proposing a synthetic view of the stakeholders that are responsible for designing, developing and operating each system component. In the _System Integration_ row, we highlight the stakeholders and the tool chain used to integrate the system components to build the final system of systems. In the last row, we report the estimated normalised costs of each engineering phase that every stakeholder expects during the life cycle of the system, thus having a broad view of the overall cost distribution. Obviously, some of the information for StkH-3 is missing because the EP information from this stakeholder is not available (black box). In this example, we demonstrate that the VCEP map can provide supplementary information not explicitly available in the Arrowhead-EP model. The VCEP map introduces the opportunity to explore at a glance which tool chain is adopted to design, develop, and operate a specific system component, the role of the stakeholders involved in the life cycle of the component, the stakeholder coverage of the value chain, the tool chain coverage of the value chain, and the normalised costs. The VCEP map can be further extended by adding new rows to show how supplementary characteristics of the value chain relate to the information already present in the map. For example, a new row can represent the level of automation of tools in the various phases of the Arrowhead-EP, or a row can focus on the adopted standards or on the main objectives reached by the different stakeholders in the Arrowhead-EPPs.