Cyber Physical Systems: A Review

Background

A CPS is a “system of sub-systems” where heterogeneous sub-systems (e.g. cyber and physical) interact in a continuous manner. These sub-systems are functionally independent but operationally dependent on each other. Developing CPSs requires modeling the relationship between different sub-systems to effectively extract knowledge from underlying data, while ensuring quality of service and handling massive data (Gupta et al. 2008). Most CPSs have real-time constraints, and hence, it is important that they meet the demands of quality of service, while remaining secure from external attacks. These requirements make the development of CPSs challenging.

Several researchers have proposed approaches for development of CPSs. Martin et al. (2012) present design tools for translating high-level specification of CPS to actual implementation on physical devices. They formulate the specification of CPS in terms of motion description languages. This helps in bridging the gap between high-level specification and the actual implementation and breaking the control tasks into small-scale motion primitives which can be easily interpreted by the system.

Talcott (2008) develops an event-based semantics for cyber physical systems. The author classifies different events according to their characteristics e.g. punctual v/s durative and uses this semantics to provide a natural way to specify components of open systems in terms of interfaces and observable behavior. Roy et al. (2011) introduce a tool for synthesizing controllers for CPSs. This tool accepts a CPS represented in the form of automata and set of differential equations and produces a system controller that enforces the given specification up to an abstraction parameter.

Dabholkar et al. (2009) discuss a methodology for systematically specializing general-purpose middleware to meet the demands of cyber physical systems which are used in different application domains. Instead of focusing on source code-level details, they raise the level of abstraction to the features the middleware offers. This helps in specializing the general-purpose middleware to the needs of domain-specific CPS.

Balasubramanian et al. (2010) present a method for ensuring QoS in networked CPSs. For isolating an application developer from the complexities of lower-level programming and QoS mechanisms, they propose use of a middleware in the CPS.