The design and analysis principles that govern smaller scale system behavior are necessary but not sufficient for larger scale systems. This is true because larger scale does not simply mean "lots of X" or "large along dimension Y." The notion of scale is subtle and multifaceted.
Cyber-physical systems (CPSs) are a natural consequence of the increased connectedness and autonomy of real-time embedded systems. Like real-time embedded systems, CPSs are characterized by a high degree of coupling between computations and physical processes.Because of this coupling, safety and timeliness properties, among others, are critical. However, increased distribution and scale make it much harder to guarantee such properties.
Ultra-large-scale (ULS) systems are interdependent webs of software-intensive systems, people, policies, cultures, and economics. They are characterized by decentralization;inherently conflicting, unpredictable, and diverse requirements;continuous evolution and deployment;heterogeneous, inconsistent, and changing elements;erosion of the people/system boundary; and routine failures. Despite such challenging characteristics, ULS systems must reliably demonstrate desirable behavior.