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In distributed applications, Brewer’s CAP theorem tells us that when networks become partitioned (P), one must give up either consistency (C) or availability (A). Consistency is agreement on the values of shared variables; availability is the ability to respond to reads and writes accessing those shared variables. Availability is a real-time property whereas consistency is a logical property. We extend consistency and availability to refer to cyber-physical properties such as the state of the physical system and delays in actuation. We have further extended the CAP theorem to relate quantitative measures of these two properties to quantitative measures of communication and computation latency (L), obtaining a relation called the CAL theorem that is linear in a max-plus algebra. This paper shows how to use the CAL theorem in various ways to help design cyber-physical systems. We develop a methodology for systematically trading off availability and consistency in application-specific ways and to guide the system designer when putting functionality in end devices, in edge computers, or in the cloud. We build on theLingua Francacoordination language to provide system designers with concrete analysis and design tools to make the required tradeoffs in deployable embedded software. 

Connected cars have the potential to transform a vehicle from a transportation platform to a platform for integrating humans with a city. To that end we introduce semantic accessors (actor based local proxies for remote services) as a novel, and powerful discovery mechanism for connected vehicles that bridges the domains of Internet of Things (IoT) composition frameworks and the semantic web of things. The primary components of this approach include a local semantic repository used for maintaining the vehicle’s perspective of its real-world context, accessors for querying and dynamically updating the repository to match evolving vehicular context information, accessors for services (such as parking) linked to a service ontology, and a swarmlet controller responsible for managing the above in accordance with user input. We demonstrate this semantic accessor architecture with a prototype Dashboard display that downloads accessors for new services as they become available and dynamically renders their self-described user interface components.