Guest Editorial: Special Issue on Cyber-Physical Systems and Services

A cyber-physical system (CPS) integrates a vast variety of static and mobile resources, including sensor and actuator networks, swarms of robots, remote-controlled vehicles, critical infrastructures, control and decision software, static data and just-in-time information from sensors, knowledge, data analytics and fusion software, eventdriven supply chains, and humans, and offers great potential for achieving tasks that are far beyond the capabilities of existing systems [1]. Individual users, organizations, and various communities can transform the vast space of cyberphysical entities into capabilities that no single entity can achieve alone. However, these capabilities do not come easily. Intelligence is needed for just-in-time composition of resources into services. Associated challenges include how to manage the vast number and diverse varieties of static and mobile physical entities, how to describe the capabilities of the cyber-physical entities, how to decompose highlevel goals into low-level control commands for the individual entities, how to achieve intelligent coordination and manage information flow among the entities. Existing technologies may be leveraged to provide partial solutions to challenges in cyber-physical systems and services (CPSS). Rapidly developing service-based technologies, such as service discovery, service composition, service adaptation, dynamic service reconfiguration, and service interaction models can be applied to integrate cyberphysical entities into desired system capabilities and to mediate the interactions among physical entities, software, information, humans, and applications. Semantic technologies can offer higher-level abstractions for specification of the capabilities of CPSs. Intelligent agents and coordination technologies can facilitate smart collaborations. Data services and information-sharing technologies can be leveraged to help manage information flow in the CPSS. Responsiveness, dependability, and security have also been major issues in cyber-physical systems [2]. Due to the vast number of entities in the CPSS, failures become inevitable. Support of robust and adaptive system integration and execution is an important topic. In the physical world, many systems are event-based and have to react in real time to newly arising situations. It can be challenging to achieve responsiveness in a large-scale and complex CPS whose components are potenially from different providers. The real-time requirement becomes even more challenging when a reactive action requires dynamic integration of cyber and physical entities into a cyber-physical service. Physical system security has long been an area demanding research. The ubiquity of physical entities makes them vulnerable to physical attacks. Such entities may become the breaching point for a CPS into which they are integrated. Further exacerbating security and especially access control concerns is the significant complexity typical of CPSs. Determining or predicting correct behavior of a system has always been a challenging issue. Due to the complexity and dynamicity of the CPSS, it is difficult to analyze and predict emerging behaviors of the composed system. Techniques for formal, experimental, or simulation-based analysis of CPSS are highly essential. Humans constitute a class of physical entities in the cyber-physical world and influence the operation of cyber entities. When a CPS has human in the loop, system behavior analysis and validation become extremely challenging. Financial issues, such as accounting, pricing decisions, and payment mechanisms, have not been widely explored for CPSS. A system may consist of cyber and physical entities from multiple owners. The potentially complex relations among the entities complicate cost estimation, pricing, and accounting. As can be seen, numerous issues in CPSS remain open for further research. This special issue presents research results related to these open challenges. Three papers were selected through a rigorous review process. The paper “Uncertainty analysis of middleware services for streaming smart grid applications” by Akkaya, Liu, and Lee investigates timing issues in the data exchange middleware that channels information flow in CPS. In almost all cyber-physical systems, a large number of sensors are utilized to monitor system conditions and facilitate decisision support for control. Thus, the timing of data exchange service is highly critical. Uncertain behaviors occur when the volume of sensor data varies significantly or the middleware topology changes due to resource constraints or failures. The authors of this paper propose a method where system entities in the data exchange middleware are modeled in a fashion that captures the system uncertainty parameters. They use a Monte Carlo simulation-based approach to determine the W. He is with the School of Computer Science, McGill University, McConnell Engineering Bldg. Room 318 3480 University, Montreal, QC, Canada, H3A 0E9. E-mail: [email protected]. S. Sedigh is with the Sarvestani Missouri University of Science and Technology, Formerly the University of Missouri-Rolla, Dept. of Electrical and Computer Engineering, 135 Emerson Electric Co. Hall, 301 W. 16th Street, Rolla, MO 65409-6524. E-mail: [email protected]. I-L. Yen is with the Department of Computer Science, University of Texas at Dallas, Richardson, Texas 75080. E-mail: [email protected].