A Framework for Efficient Service Composition in Cyber-Physical Systems

Service-oriented architecture (SOA) provides the concept of packaging available functionalities as interoperable services within the context of various domains that use it. With rapid advances in SOA technologies and the growing availability of web services, the problem of composing a set of web services to achieve complex systems is becoming more practical. In the context of cyber-physical systems where hardware and software are coupled together to realize integrated systems, there are special characteristics and requirements. One of these is that most service providers are physical entities with their own states and properties. The constraint that follows is that a given entity might not be able to perform all the services it can provide at the same time. In fact, “multi-threading” for physical entities is rarely possible. This requires specific service modeling techniques to enable the use of SOA methods for this domain. Another characteristic is that due to the dynamic nature of cyber-physical worlds, the service composition procedure must be dynamically adaptive. In terms of AI planning, which is one of the fundamental techniques for service composition, not only the initial state and the goal are dynamic, but the planning domain also needs to be generated dynamically to provide the complete input to the underlying planner. Taking all these characteristics and requirements into consideration, we develop an ontology model for physical entity specification. Based on this model, another widely used service ontology model, OWL-S is extended to accurately model the characteristics of service providers in the context of cyber-physical worlds. Further, a technique for generating planning domain based on task requirements is developed.