# System of Systems Lifecycle Management--A New Concept Based on Process Engineering Methodologies
## 2 An Overview on Common Lifecycle Management Models
### Gap: A Need for System of Systems Lifecycle Management  
In the SOA approach, the term service is used as an entity for information exchange between the service provider and consumer systems. If this spectrum is extended, we can introduce the SoS concept, where the systems work together to achieve a more complex target or a higher purpose. An SoS is defined as the result of a set or arrangement of independent systems that are integrated and combined. To distinguish SoS from more traditional systems, it is necessary to understand some of its characteristics. According to [PERSON] [60], five main dimensions can characterize an SoS concerning other vast and complex but monolithic systems:  
1. Operational independent: a system is an independent part of an SoS, and it can be used to compose other SoS.
2. Management independent: each system could be managed independently.
3. Evolutionary development: the SoS is flexible and modular enough to evolve with functions and purposes added, removed, and modified along its lifetime.
4. Emergent behavior: its functionalities cannot be mapped into any component of the system, i.e., the behaviors are emergent properties of the overall SoS and cannot be assigned to any of its components.
5. Geographical distribution: the system components are physically distributed.  
Taking into account the previously described lifecycle management approaches, it can be seen that no single management model covers the characteristics of SoS. The ALM is mainly for computer programs; therefore, it cannot entirely satisfy all of the requirements of SoS. The ILM can serve as a sound basis on how to control the information flow between the lifecycle stages. However, it alone does not provide enough description for complete SoS management, although it must be integrated into the SoS. SDLC is mainly concerned with how to develop code. The scope and emphasis are preferably on the development techniques, which is, on the one hand, a significant part of SoS but, on the other hand, just one of its essential tools. The SLM is much closer to the solution, but as its name shows, the focus is merely on the services and their management. However, managing the SoS is a much more complicated task. The lifecycle stages of PLM are relevant for SoS, but the perspective does not entirely align with SoS. Consequently, PLM is built around product-specific processes that are not altogether suitable for systems. However, similarly to SLM, the PLM strategies should also be taken into account for SoS. Table 1 serves with a brief overview about the main benefits and gaps of the examined lifecycle management models. Based on the results, it can be stated that there is no lifecycle management model yet, which can satisfy in itself the SoS-related requirements.  
To achieve the most fitting model, the tasks to be solved were divided into two parts. Since the core of SoSLM relies heavily on the terminology used by PLM models, the aim was first to develop a PLM model, especially for IIoT systems. Section 5 describes the reason behind it and the proposed model accordingly. However, still, the target remains a comprehensive model to SoS architectures, for which the requirements were not entirely covered by the developed PLM model. Thus, in the second step, the developed IIoT-compliant PLM model was extended to the service-oriented expectations, creating an SoSLM model that can be read in Section 7. The presented lifecycle management approaches are based mostly on process engineering and ITSM frameworks. Thus, the processes recommended by the widely used and accepted frameworks [9; 10; 11] were examined during the formation of the models. The literature review is included in the next section.