The key topic of this site is systems-of-systems. But what is that? Here, I will explain some key definitions, and provide an overview of some of the challenges in the area.
The term systems-of-systems (SoS) has been around for a few decades, and is seen as an important concept, e.g., by the European Union in its Digital Agenda. Still, a lot of people seem to equate SoS with large and complex system in general, and not give it any more specific meaning. However, at least in the research community, there is a rather clear and widely accepted definition put forward already 20 years ago by Mark Maier. He identified five key dimensions:
- Operational independence of the elements. The constituent systems can operate independently in a meaningful way, and are useful in their own right.
- Managerial independence of the elements. The constituent systems not only can operate independently, but they do operate independently even while being part of the SoS. They are acquired separately.
- Evolutionary development. The SoS does not appear fully formed, and functions and purposes are added based on experience.
- Emergent behavior. The principal purposes of the SoS are fulfilled by behaviors that cannot be localized to any individual constituent system.
- Geographical distribution. The constituent systems only exchange information and not substantial quantities of mass or energy.
An intuitive interpretation of this is that an SoS is a group of independent collaborating systems. The elements of an SoS, called constituent systems, retain an operational and managerial independence, but when combined in a certain way, they provide together a new capability that is emergent from their cooperation.
In the spring of 2015, I had the pleasure of leading a project on developing a strategic research and innovation agenda for SoS in Sweden. The project was sponsored by the Government Agency for Innovation, VINNOVA, and it was carried out through a set of workshops with representatives from large and small companies with an interest in the subject, many of them being member of the Swedish INCOSE chapter. There were also workshops gathering Scandinavian academic researchers in the field.
Much of the research previously done on SoS has been focusing on military and similar applications in a US setting. In our work, it soon became apparent that a broader view was needed, taking into account civilian and industrial applications as well. This opens up many important avenues for research, and a key conclusion of the agenda is that there is a need for capabilities to rapidly develop trustworthy SoS. This is a grand challenge to the area in light of the digitization of society, and it requires advances in many areas. A set of challenges were identified that require particular attention:
- Theoretical foundations. There is a need in general for a more advanced theoretical foundation for the SoS field, including a more precise language for describing and reasoning about SoS. Specific topics include emergence, which is currently not well understood, but is essential since creating an emergent behavior is usually the raison d’être for the SoS. The principles for the design of mechanisms that create the desired emergent behavior and properties is also a key topic which is in its infancy.
- Socio-technical aspects. Many of the SoS challenges in practice relate to the organizations that manage the SoS and its constituent systems, and the need for agreements and negotiations between them. Finding efficient ways to deal with this is essential for rapid SoS development. Also, as automation progresses, a more fundamental understanding of the interplay between the technical systems and the people and organizations is needed, as the distribution of work between them changes.
- Architecture. Architecture is and will remain a central part of SoS engineering, and further refinement of methods for describing and evaluating the architecture is needed. In particular, the architecture is an enabler for rapid assembly of constituent systems into an SoS, simply because a good architecture will make the pieces fit better together, thus requiring less time for adjustments. It is also an enabler for trustworthiness, by describing clear principles and distribution of responsibilities between the constituent systems. There is also a need to focus on the architecture of systems that could become a constituent, and find ways of building flexibility into those systems from the beginning to make them adaptable to the needs of a future SoS, thereby reducing the duration of SoS integration.
- Modeling and simulation. Modeling involves describing the SoS in a simplified way, and has a strong relation to architecture. Capturing the essential structures and behavior in a concise way is an enabler for an efficient communication between the involved organizations, and thus leading to more rapid agreements. Many of the existing modeling frameworks can be improved, in particular there is a need for light-weight versions that can be used to rapidly capture the essentials. Models are also used as input to simulations, which allow for early verification of the emergent properties. In particular, co-simulations where existing models of constituent systems can be integrated are of importance, especially when complemented with efficient ways of visualizing the effects for decision makers. Modeling and simulation are thus a foundation for rapid SoS engineering, allowing fast iterations of design and evaluation. Their value in establishing trust, through extensive analysis of, e.g., safety, merits further research.
- Interoperability. To be able to link the constituent systems together, interoperability is a key. Techniques for achieving this exist, especially on the syntactic and to some extent semantic levels, but further development is needed to handle pragmatic and organizational interoperability. Achieving interoperability is largely founded on standards, which take a very long time to develop, and there is an urgent need of finding more flexible mechanisms that allow rapid achievement of interoperability, even between existing systems.
- Trust. There are multiple dimensions of trust that need to be handled, including dependability, robustness, security, and privacy. The particular aspects related to trust in SoS are caused by the operational and managerial independence of the constituent systems, and maintaining trust over the evolution. An overarching challenge lies in combining trust with rapid development. For this, new techniques need to be developed, and the most promising way forward is based on systems thinking, where progress is already being made in the safety area. This should be combined with simulation based approaches which allow rapid reevaluation of trust during system evolution.
- Business and legal aspects. Much of existing knowledge about SoS comes from government driven applications such as defense, and there is a lack of understanding of business models for commercially oriented applications. This includes also the design of mechanisms for keeping the SoS together, including both motivations and punishments for constituent systems. In many situations, legal contracts are needed, and to avoid lengthy negotiations, template contracts should be developed for rapid conclusion of the necessary agreements. There is also a lack of understanding of liability issues related to an SoS, when severe losses result from the emergent behavior of the SoS rather than from an individual constituent system.
- Processes and methods. Although many of the principles of general systems engineering (SE) also apply to SoS as well, there are also fundamental differences. The SE processes are typically characterized by working top-down, and by tackling complexity through decomposition. The SoS processes need to be bottom-up and focusing on integration of existing element. To this should be added the need for speed, which is not one of the strengths of SE. There is a need for a better understanding in general of the SoS processes, and in particular how to efficiently organize cross-organizational development. In this, management and leadership aspects play important roles.
The agenda document discuss these challenges in more detail and also the topic of standardization which is important, but to some extent in conflict with rapidity, since standards can only be developed once the understanding of technical solutions has matured.
The above challenges are driving my current and future research in the SoS area, and I will return to some of them in more detail in future posts.